Acute Pancreatitis Imaging

Overview

According to the 1992 International Symposium on Acute Pancreatitis, acute pancreatitis is defined as an acute inflammatory process of the pancreas with variable involvement of other regional tissues or remote organ systems (see the image below).^[1] Acute pancreatitis is classified further into mild and severe forms. Mild acute pancreatitis is associated with minimal organ dysfunction and uneventful recovery. Severe acute pancreatitis is associated with pancreatic necrosis and may lead to organ failure and/or local complications.^{[2, 3, 4]}
Acute pancreatitis. Focal pancreatitis involving pancreatic head. Pancreatic head is enlarged with adjacent ill-defined peripancreatic inflammation and fluid collections. Local complications of acute pancreatitis include fluid collections, pseudocyst formation, abscess, pancreatic necrosis, hemorrhage, venous thrombosis, and pseudoaneurysm formation (see the images below).^[5] A pseudocyst is defined as a collection of pancreatic juice enclosed by a wall of fibrous or granulation tissue. A pseudocyst lacks a true epithelial lining and often communicates with the pancreatic duct. A pancreatic abscess is a circumscribed intra-abdominal collection of pus. The development of both pseudocyst and abscess usually requires 4 or more weeks from the initial clinical onset of acute pancreatitis.^[6] Pancreatic necrosis is defined as focal or diffuse areas of nonviable pancreatic parenchyma; it usually is associated with peripancreatic fat necrosis. Necrosis usually develops early in the course of acute pancreatitis.^[7]
Acute pancreatitis. Pancreatic abscess. Large, relatively well-circumscribed heterogeneous collection containing gas bubbles inferior to the pancreatic head. This collection was drained successfully and percutaneously via a 12Fr pigtail catheter. Acute pancreatitis. Pancreatic necrosis. Note the nonenhancing pancreatic body anterior to the splenic vein. Also present is peripancreatic fluid extending anteriorly from the pancreatic head. Acute pancreatitis. Pancreatic necrosis. Approximately 50% of the pancreatic gland does not display enhancement after contrast administration. Gallstones and alcohol abuse are the most common causes of acute pancreatitis, accounting for 60-80% of cases. Other causes include blunt trauma to the abdomen, iatrogenic trauma (postoperative trauma, endoscopic retrograde cholangiopancreatography), hypertriglyceridemia, hypercalcemia, drug-induced, infectious etiologies (eg, mumps, cytomegalovirus), congenital anomalies (pancreas divisum, choledochocele), ampullary or pancreatic tumors, vascular abnormalities (atherosclerotic emboli, hypoperfusion, vasculitis), cystic fibrosis, and Reye syndrome. These miscellaneous causes account for approximately 10% of cases of acute pancreatitis. In approximately 10-25% of patients, no underlying cause is found.^{[8, 9, 10]}

Preferred examination

Contrast-enhanced computed tomography (CECT) is the standard imaging modality for the evaluation of acute pancreatitis and its complications. Using non–contrast-enhanced CT, clinicians can establish the diagnosis and demonstrate fluid collections but cannot evaluate for pancreatic necrosis or vascular complications.
CECT allows complete visualization of the pancreas and retroperitoneum, even in the setting of ileus or overlying bandages from a recent surgical procedure. CECT can help detect almost all major abdominal complications of acute pancreatitis, such as fluid collections, pseudocysts, abscesses, venous thrombosis, and pseudoaneurysms. In addition, CECT can be used to guide percutaneous/interventional procedures such as diagnostic fine-needle aspiration or catheter placement. CECT may be performed on severely ill patients including intubated patients. Lastly, CECT can be used as a prognostic indicator of the severity of acute pancreatitis.
Other adjunctive imaging modalities include ultrasonography (US), MRI, and angiography. US is especially useful in the diagnosis of gallstones and follow-up observation of pseudocysts. US also can be used to detect pancreatic pseudoaneurysms. The diagnostic efficacy of MRI is comparable to that of CECT, although MRI examination is more time consuming and costly.^{[11, 12, 13]} Angiography is primarily used to help diagnose the vascular complications of acute pancreatitis.^{[14, 15, 16, 17, 18]}
CT and US are the guidance modalities of choice in performing diagnostic fine-needle aspiration and percutaneous drainage of fluid collections. Diagnostic fine-needle aspiration is performed to distinguish infected from noninfected pseudocysts and to delineate pancreatic abscess from infected necrosis. The aspirate should be sent at once for Gram stain and subsequent aerobic, anaerobic, and fungal cultures. Treatment regimens for these entities differ.^{[19, 20]}

Limitations of techniques

The usefulness of CECT is limited in patients who are allergic to intravenous (IV) contrast or have renal insufficiency. Patients who have severe acute pancreatitis often require multiple scans to assess progress and/or complications. This necessitates significant radiation doses.
In addition, CECT is far less sensitive than US in detecting gallstones or biliary duct stones, a common cause of acute pancreatitis. Therefore, if gallstones or an impacted common bile duct stone is not seen on CT, US is necessary to document the presence or absence of gallstones.

Radiography

Plain films of the abdomen are part of the initial diagnostic workup of acute abdominal pain.^[21] Findings on plain films are nonspecific but are suggestive of acute pancreatitis. The most commonly recognized radiologic signs associated with acute pancreatitis include the following:

• Air in the duodenal C-loop
• The sentinel loop sign, which represents a focal dilated proximal jejunal loop in the left upper quadrant
• The colon cutoff sign, which represents distention of the colon to the transverse colon with a paucity of gas distal to the splenic flexure

In a review of 73 cases by Rifkind et al, other plain film findings included obscuration of the psoas margin, increased epigastric soft tissue density, increased gastrocolic separation, gastric curvature distortion, pancreatic calcification, and pleural effusion (usually on the left).^[22] It is noteworthy that the abdominal plain film can be completely normal in patients with acute pancreatitis.

Computed Tomography

CECT scanning of the abdomen and pelvis is the standard imaging modality for evaluating acute pancreatitis and its complications. Both IV and oral contrast should be administered. Imaging protocols vary, but the most important unifying point is to obtain thin-section images during the peak of pancreatic arterial perfusion. This usually can be acquired by imaging 30-40 seconds after the administration of iodinated contrast at 3-4 mL/s using helical CT. Some advocate the use of water as a negative contrast agent, because barium in the duodenal sweep could potentially obscure a high-attenuation stone. (See the image below.)
Acute pancreatitis. Pancreatic necrosis. Note the nonenhancing pancreatic body anterior to the splenic vein. Also present is peripancreatic fluid extending anteriorly from the pancreatic head. Freeny recommends obtaining CECT in the following situations^[23] :

• Patients in whom the clinical diagnosis is in doubt
• Patients with hyperamylasemia and severe clinical pancreatitis, abdominal distention, tenderness, high fever, and leukocytosis
• Patients with a Ranson score greater than 3 or an APACHE score greater than 8
• Patients who do not manifest rapid clinical improvement within 72 hours of initiation of conservative medical therapy
• Patients who demonstrate clinical improvement during initial medical therapy but then manifest an acute change in clinical status, indicating a developing complication

Typical CT findings in acute pancreatitis include focal or diffuse enlargement of the pancreas, heterogeneous enhancement of the gland, irregular or shaggy contour of the pancreatic margins, blurring of peripancreatic fat planes with streaky soft tissue stranding densities, thickening of fascial planes, and the presence of intraperitoneal or retroperitoneal fluid collections. The fluid collections most commonly are found in the peripancreatic and anterior pararenal spaces but can extend from the mediastinum down to the pelvis.
Complications of acute pancreatitis, such as pseudocysts, abscess, necrosis, venous thrombosis, pseudoaneurysms, and hemorrhage, can be recognized with CECT.^[24]
A pseudocyst appears as an oval or round water density collection with a thin or thick wall, which may enhance.
A pancreatic abscess can manifest as a thick-walled low-attenuation fluid collection with gas bubbles or a poorly defined fluid collection with mixed densities/attenuation. Gas bubbles are not specific for infection, and the diagnosis of a pancreatic abscess usually requires percutaneous fine-needle aspiration to confirm the presence of pus.
Necrotic pancreatic tissue is recognized by its failure to enhance after IV contrast administration. Balthazar et al point out that the normal unenhanced pancreas has CT attenuation measuring 30-50 Hounsfield units (HU) and that after IV contrast, the pancreas should display attenuation measuring 100-150 HU.^[25] A focal or diffuse well-marginated zone of unenhanced parenchyma (>3 cm in diameter or >30% of pancreatic area) is considered a reliable CT finding for the diagnosis of necrosis. It should be noted that pancreatic necrosis may be radiologically indistinguishable from a pancreatic abscess.
Venous thrombosis can be identified through a failure of the peripancreatic vein (eg, splenic vein, portal vein) to enhance or as an intraluminal filling defect.
Associated gastric varices may be identified.
A pseudoaneurysm usually appears as a well-defined round structure with a contrast-enhancement pattern similar to that of the aorta and other arteries. Hemorrhage appears as high-attenuation fluid collections. Active bleeding is seen as contrast extravasation.
CECT can be used to assess the severity of acute pancreatitis and to estimate the prognosis. Balthazar et al developed a grading system in which patients with acute pancreatitis are classified into 1 of the following 5 grades^[25] :

• Grade A - Normal-appearing pancreas
• Grade B - Focal or diffuse enlargement of the pancreas
• Grade C - Pancreatic gland abnormalities associated with peripancreatic fat infiltration
• Grade D - A single fluid collection
• Grade E - Two or more fluid collections

In patients with pancreatitis of grade A or B, the disease has been shown to follow a mild, uncomplicated clinical course; most complications occur in patients with pancreatitis of grade D or E.
Balthazar et al further constructed a CT severity index (CTSI) for acute pancreatitis that combines the grade of pancreatitis with the extent of pancreatic necrosis.^[25] The CTSI assigns points to patients according to their grade of acute pancreatitis as well as the degree of pancreatic necrosis. More points are given for a higher grade of pancreatitis and for more extensive necrosis. Patients with a CTSI of 0-3 had a mortality of 3% and a complication rate of 8%. Patients with a CTSI of 4-6 had a mortality rate of 6% and a complication rate of 35%. Patients with a CTSI of 7-10 had a 17% mortality rate and a 92% complication rate.
Grade of acute pancreatis and the points assigned per grade are as follows:

• Grade A - 0 points
• Grade B - 1 point
• Grade C - 2 points
• Grade D - 3 points
• Grade E - 4 points

Grade of necrosis and the points assigned per grade are as follows:

• None - 0 points
• Grade 0.33 - 2 points
• Grade 0.5 - 4 points
• Grade higher than 0.5 - 6 points

Degree of confidence

In a prospective study of 202 patients, Clavien et al reported a 92% sensitivity and 100% specificity in diagnosing acute pancreatitis via CECT.^[26] Balthazar et al reported an overall accuracy of 80-90% in the detection of pancreatic necrosis.^[25] Small areas of necrosis involving less than 30% of the pancreas can be missed. Nevertheless, the extent of pancreatic necrosis has been found to correlate well with operative findings and clinical severity. In a study by Block et al, the positive predictive value of CECT for pancreatic necrosis was found to be 92%.^[27]

False positives/negatives

The pancreas may appear normal in approximately 25% of patients with mild pancreatitis. In the acute phase of pancreatitis, a small number of patients will have a false-positive diagnosis for necrosis due to massive interstitial edema and vasoconstriction of the vascular arcades. Repeat CT within a few days may show normal pancreatic enhancement.

Magnetic Resonance Imaging

Although CT has long been the mainstay for imaging acute pancreatitis and its complications, MRI is an excellent alternative imaging modality.^{[28, 29, 30]} MRI is a viable alternative in situations in which CECT is contraindicated, such as in patients with contrast allergy or renal insufficiency. (See the images below.)
Acute pancreatitis. Focal pancreatitis involving pancreatic head. Pancreatic head is enlarged with adjacent ill-defined peripancreatic inflammation and fluid collections. Acute pancreatitis. Pancreatic abscess. Large, relatively well-circumscribed heterogeneous collection containing gas bubbles inferior to the pancreatic head. This collection was drained successfully and percutaneously via a 12Fr pigtail catheter. Acute pancreatitis. Pancreatic necrosis. Approximately 50% of the pancreatic gland does not display enhancement after contrast administration. In addition to T1-weighted and fast spin-echo T2-weighted sequences, 2-dimensional Fourier transform (FT) and 3-dimensional FT gradient-echo sequences can be used to rapidly image the pancreas during patient breath holds; this reduces the artifacts related to physiologic motion.
Bolus contrast administration of gadolinium chelates can be used to assess for pancreatic necrosis. The quality of upper abdominal imaging is enhanced further with the use of phased-array surface coils and fat-suppression techniques.
Detrimental effects of physiologic motion can be reduced further using ultrafast T2-weighted sequences, such as single-shot fast spin-echo or half-Fourier acquisition single-shot turbo-spin echo (HASTE) sequences. Subsecond image acquisitions provide quality diagnostic images even in uncooperative or tachypneic patients. These sequences also are used routinely for depicting the biliary tract in magnetic resonance cholangiopancreatography (MRCP). The normal pancreas demonstrates relatively high signal intensity on T1-weighted images with fat suppression.
The morphologic changes of acute pancreatitis are similar on CT and MRI.
The pancreas may be enlarged focally (usually the pancreatic head) or diffusely. Acute inflammatory changes appear as strands of low signal intensity in the surrounding peripancreatic fat.
Complications of acute pancreatitis also can be identified. Hemorrhage is characterized by T1 shortening or high signal intensity on T1-weighted sequences with fat suppression. Peripancreatic fluid collections, pseudocysts, and abscesses are recognized by their high signal intensity on T2-weighted sequences. Devascularized or necrotic portions of the pancreas fail to enhance on dynamic gadolinium-enhanced images. MRI also may be better than CT in detecting areas of sterile pancreatic necrosis in what appear to be simple pseudocysts on CT.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
As of late December 2006, the FDA had received reports of 90 such cases of NSF/NFD . Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

Degree of confidence

In a small study by Saifuddin et al, MRI was found to be equivalent to CECT in helping assess the location and extent of peripancreatic inflammatory changes and fluid collections.^[31] In addition, MRI was found to be equivalent in helping assess the degree of pancreatic necrosis. Chalmers et al showed that MRI is more effective than CECT in helping characterize the content of fluid collections and in helping demonstrate gallstones.^[32]

False positives/negatives

In mild cases of acute pancreatitis, the pancreas can appear completely normal on MRI. MRI also is limited in detecting gas and calcifications.

Ultrasonography

Jeffrey recommends obtaining images of the pancreas and the peripancreatic compartments, such as the lesser sac, anterior pararenal space, and transverse mesocolon, by scanning in the supine, longitudinal, transverse, semi-erect, and coronal planes.^{[33, 34, 35]} However, regions of the pancreas may not be visible by US because of overlying bowel gas.
The spleen can be used as an acoustic window to image the pancreatic tail.
Laing et al advise radiologists to scrutinize the intrapancreatic portion of the common bile duct carefully for biliary stones.^[36]
Doppler techniques should be used to assess vascular complications of acute pancreatitis, such as venous thrombosis and pseudoaneurysm formation.
US is the most sensitive modality for concomitantly evaluating the biliary tree/gallbladder.
More definitive findings include a diffusely enlarged hypoechoic gland. Focal enlargement of the pancreatic head and body also may be seen.
Complications of acute pancreatitis may be identified. Peripancreatic free fluid collections are identified as ill-defined anechoic collections. The fluid collections may demonstrate internal echoes/debris or septations if hemorrhage or a superimposed infection has occurred.
Extrapancreatic spread of acute pancreatitis may be the only sonographic manifestation of acute pancreatitis in some patients.
Pseudocysts appear as well-defined round or oval anechoic fluid collections with through transmission. Infected and noninfected pseudocysts are indistinguishable from each other sonographically. US often is used to monitor the resolution of pancreatic pseudocysts.
A pancreatic abscess may appear as a complex cystic structure with internal debris/septations and, possibly, echogenic gas bubbles. A pseudoaneurysm often appears as a cystic mass with turbulent arterial flow within the mass.
Acute hemorrhage may be identified as a hyperechoic fluid collection. Venous thrombosis can be identified as an intraluminal filling defect. Associated gastric varices may be appreciated.

Degree of confidence

A primary limitation of US is that often the pancreas cannot be visualized secondary to overlying bowel gas. Neoptolemos et al report a sensitivity of 67% and a specificity of 100% in the diagnosis of acute pancreatitis by US.^[37]

False positives/negatives

The pancreas may appear completely normal in mild cases of acute pancreatitis.

Angiography

Vascular complications of acute pancreatitis result from the proteolytic effects of the pancreatic enzymes that cause erosion of blood vessels, which often results in pseudoaneurysm formation or free rupture. The splenic artery, followed by the pancreaticoduodenal and gastroduodenal arteries, are affected most commonly. The left gastric, hepatic, and small intrapancreatic arteries are involved less often.
If acute hemorrhage or pseudoaneurysm is suspected or diagnosed by US or CECT, a celiac/superior mesenteric arteriogram should be performed to definitively assess the extent of vascular involvement. In addition, permanent or temporary therapeutic embolization can be performed. The primary contraindication for angiography is a hemodynamically unstable patient.
The precise bleeding point is identified by noting free contrast extravasation. Once the site of pseudoaneurysm or the source of active bleeding is identified, it can be treated by Gelfoam embolization, various coil occlusion devices, or tissue adhesives (eg, bucrylate). Superselective microcoil embolization also has been advocated by Reber et al.^[38] Vujic has suggested using small Gelfoam particles to control diffuse pancreatic surface bleeding.^[39] Diffuse bleeding from the gland may appear angiographically as a prominent blush.
Vujic reports that embolization may be used as a temporizing measure to slow bleeding so that the patient may be operated on electively.^[39] This temporary therapeutic procedure involves selective or nonselective Gelfoam embolization or balloon occlusion of the main celiac trunk.
Complications of celiac/superior mesenteric arteriography and embolization include arterial injury such as thrombosis, dissection, or rupture, distal embolization, ischemia of visceral organs such as the spleen and bowel, coil malpositioning, and rebleeding.
Venous thrombosis of the splenic vein and/or collateral venous pathways also may be diagnosed via selective angiography.

Degree of confidence

Precise identification of the pseudoaneurysm or bleeding site is crucial for effective treatment. Gambiez et al and Boudghene et al have reported sensitivities of 93% and 96%, respectively, in identifying the bleeding site.^{[40, 41]} Success rates of 79% and 78% have been reported by Mandel et al and Boudghene et al, respectively, in embolizing pancreatic pseudoaneurysms.^{[42, 41]}

False positives/negatives

Koehler et al have noted that failure to identify the bleeding source may be because of intermittent arterial bleeding, bleeding from a larger surface area, and venous bleeding.^[43] Gambiez et al have reported improper identification of the bleeding artery, inability to catheterize the bleeding vessel selectively, and inexperience of the angiographer as causes of embolization failure.^[40]

Imaging in Lung Cancer Staging

Overview

Lung cancer is the leading cause of cancer-related deaths in men and women worldwide. The incidence of lung cancer in women has increased even faster than the overall incidence has, reflecting the increased use of tobacco among women in the past 30 years.^{[1, 2, 3]}
The most important prognostic indicator in lung cancer is the extent of disease. The Union Internationale Contre le Cancer (UICC) and the American Joint Committee for Cancer Staging (AJCC) developed the tumor, node, and metastases (TNM) staging system. This system takes into account the degree of spread of the primary tumor, represented by T; the extent of regional lymph node involvement, represented by N; and the presence or absence of distant metastases, represented by M. The TNM system is used for all lung carcinomas except small cell lung cancers (SCLCs), which are staged separately.
Non–small cell lung cancer (NSCLC), for which the TNM system is the most widely used staging scheme, accounts for approximately 75% of all lung cancers. NSCLC is subdivided into adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. Despite their histologic and clinical differences, these carcinomas share a similar prognosis and are managed in a similar way. (See the images below.)
Image of a 1.8-cm peripheral carcinoma in the lingula, stage T1. Right middle lobe peripheral carcinoma, 3.5 cm in diameter, stage T2. Right apical carcinoma, stage T3. Right hilar mass invading the mediastinum, stage T4, with mediastinal lymphadenopathy, N3. Computed tomography (CT) scan screening can detect most cases of lung cancer. Surgery is the treatment of choice for NSCLC if the primary tumor is resectable and if metastatic disease is absent. Chemotherapy and radiation therapy are used to treat tumors that are unresectable because of intrathoracic spread or distant metastases. (SCLC metastasizes early and has a worse outcome than NSCLC.)
For excellent patient education resources, visit eMedicine's Cancer and Tumors Center. Also, see eMedicine's patient education articles Lung Cancer, Understanding Lung Cancer Medications, and Non-Small-Cell Lung Cancer.

Staging of Primary Tumors

The stages in the TNM system represent the nature and extent of spread of a neoplasm and, thus, the therapeutic options and prognosis in individual patients. Stages also provide a standard by which various therapies can be compared. A combination of clinical, laboratory, radiologic, and pathologic investigations are used to stage various neoplasms.^{[4, 5]}

Conventional chest radiography

Conventional chest radiographs (CXRs) usually demonstrate the size of the lung tumor, especially in peripheral lesions. Central tumors may be associated with atelectasis or obstructive pneumonitis. The proximal extent of central tumors is determined with bronchoscopy.
CXRs may also show a pleural effusion, direct extension into the chest wall with destruction of the ribs or vertebrae, phrenic nerve involvement with elevation of a hemidiaphragm, or mediastinal widening due to lymphadenopathy. In the absence of these signs, CXRs are unreliable in detecting invasion of the chest wall, diaphragm, or mediastinum, and CT or MRI is required to assess these conditions.

Computed tomography scanning

Contrast-enhanced helical CT scanning of the thorax and abdomen, including the liver and adrenal glands, is the standard radiologic investigation for staging lung cancers. The primary tumor should be measured by using lung window settings in 2 dimensions: the maximum long axis and the largest diameter perpendicular to the long axis.^{[6, 7]}
CT scanning reliably depicts mediastinal invasion, provided that the tumor surrounds the major mediastinal vessels or bronchi. A tumor that abuts the mediastinum cannot be considered invasive, even if the fat plane between the mediastinum and mass is obliterated.
CT scan criteria for resectability include the following:

• Contact between mass and mediastinum of less than 3 cm
• Circumferential contact between the mass and aorta of less than 90°
• Presence of a fat plane between the mass and mediastinum

Criteria for nonresectability include the following:

• Involvement of the carina
• Tumor surrounding, encasing, or abutting the aorta. Main or proximal portions of the right or left pulmonary arteries, or esophagus by more than 180°

Tumors with more than 3 cm of contact and no obvious invasion may be difficult to stage. Neither CT scanning nor MRI can be used to distinguish tumor invasion of mediastinal fat from inflammatory changes.

Magnetic resonance imaging

MRI is superior to CT in assessing the pericardium, heart, and great vessels. Coronal images are useful in demonstrating the extent of tumor in the subcarinal region, aortopulmonary window, and superior vena cava. However, it is limited by poorer spatial resolution, as compared with that of CT, and by cardiac and respiratory motion artifacts; however, the magnitude of these limitations has diminished with newer MRI scanners.
MRI may be used instead of CT in patients who have had previous adverse reactions to iodinated contrast media and in patients with significant renal impairment, because MRI does not require the use of intravenous enhancement with iodinated contrast media.
The overall difference in accuracy between MRI and CT is not significant. The sensitivity of CT is 63%, and that of MRI is 56%. In the distinction of T3 and T4 tumors from less extensive tumors, the specificity of CT is 84%, and that of MRI is 80%.

Positron emission tomography scanning

The role of positron emission tomography (PET) scanning has become more widespread since the turn of the 21st century. It is indicated in the assessment of indeterminate pulmonary nodules and staging. Fluorodeoxyglucose (FDG)-PET is superior to CT in differentiating between malignant and benign tumors. The preoperative use of PET has led to a reduction in the number of unnecessary thoracotomies in patients considered to be operable on the basis of CT and clinical criteria. The combination of CT and PET scanning improves radiotherapy planning and it is to be expected that combined CT-PET–guided planning devices will further refine 3-dimensional conformal radiotherapy.^{[8, 9, 10, 11]}

Staging of Mediastinal Lymph Nodes

Hilar (N1), ipsilateral (N2), or contralateral (N3) mediastinal lymph node metastases are often present at the time of presentation. The N stage is important, because it determines the prognosis and the suitability of curative surgery. On CXRs, CT scans, and MRIs, nodal enlargement may indicate nodal involvement; however, this finding may be inaccurate. Normal-sized nodes may contain metastases, and nodes may be enlarged due to inflammatory causes although they contain no malignant cells. Furthermore, the classification of nodes and the normal range of the size of mediastinal nodes have been disputed.
On the accepted lymph node map described by the AJCC and UICC in 1997, nodes in position 10 are designated as hilar nodes. The short-axis diameter is the most reliable measurement of lymph node size on CT scans. A short-axis diameter greater than 10 mm is abnormal regardless of the nodal station.

Conventional chest radiography

Chest radiography is inferior to CT scanning in the detection of mediastinal lymph node metastases. It has a sensitivity of only 10-30%, although its specificity (90%) is higher than that of CT scanning.

Computed tomography scanning

The visualization of mediastinal nodes is facilitated by the use of spiral or multisection CT, thin (5-mm) sections, the presence of mediastinal fat, and intravenously administered contrast material.
The reported sensitivity and specificity of CT scanning in the detection of mediastinal nodes vary considerably, with ranges of 40-84% and 52-80%, respectively. This variability reflects interobserver variability and differences in the size criteria for abnormal lymph nodes, in patient populations, and in the diagnostic criterion standard. CT scanning is more specific in populations in Europe with a low incidence of granulomatous disease than it is in populations in the United States, which have a high incidence of histoplasmosis; rates are 80-90% and 50-70%, respectively.
The negative predictive value of CT scanning is about 85%; as a result, patients with normal mediastinal appearances undergo thoracotomy. Mediastinoscopy or thoracoscopy is required during biopsy of enlarged noncalcified lymph nodes before surgery is ruled out.

Magnetic resonance imaging

Like CT scanning, MRI size criteria are used to identify nodal involvement, and these are comparable to those used at CT scanning. However, MRI can be used to distinguish nodes from vessels without intravenous contrast enhancement. Also, direct imaging in the sagittal and coronal planes is possible; this is helpful in the assessment of the subcarinal and aortopulmonary regions.

Positron emission tomography scanning

Unlike MRI and CT scanning, PET scanning does not rely on the anatomic assessment of nodes. It is primarily a metabolic imaging technique that relies on a biochemical difference between normal and neoplastic cells. Mediastinal nodes containing tumor have an increased uptake of FDG, a glucose analogue labeled with fluorine-18 (¹⁸ F), a positron emitter.
Although its high cost and limited availability blunted the impact of PET scanning in Western countries, changes in regulations and reimbursement in the United States have increased the use of this modality and access to PET centers.
PET is superior to CT in the assessment of mediastinal nodal metastases. In patients with N2 disease, PET had a sensitivity of 83% and a specificity of 94%, compared with a sensitivity of 63% and a specificity of 73% with CT. The superiority of PET is even more marked in the assessment of hilar nodes, for which it has a 73% sensitivity and a 76% specificity, compared with an 18% sensitivity and an 86% specificity with CT.
FDG-PET enables accurate staging of regional lymph node disease in patients with stage I NSCLC. A negative PET scan in these patients suggests that mediastinoscopy is unnecessary and that thoracotomy may be performed. FDG-PET is justified as a supporting staging measure in cases presenting unclear differentiation between N2 and N3 after conventional staging.
In about 35% of cases first staged with CT, the disease is upstaged after subsequent PET, with resultant changes in management. Nevertheless, PET can produce some false-negative results. In one study, 5 of 39 patients with negative PET scans had a carcinoma, as revealed with pathologic staging. In 4 of these patients, correlation with CT findings led to the correct conclusion. Thus, PET and CT are complementary, because the visual information on CT enables anatomic discrimination between hilar and mediastinal nodes and more accurate localization of the hot spots. The sensitivity of PET combined with CT was 93%, and the specificity was 97%.
Studies suggest that FDG-PET is more sensitive but less specific in cases in which lymph node enlargement is present on CT scan. For patients with lymph nodes measuring 16 mm or more on CT and a negative FDG-PET result, the post-test probability for N2 disease was 21%. These patients should be scheduled for mediastinoscopy before possible thoracotomy to prevent too many unnecessary thoracotomies in this subset. However, for patients with lymph nodes measuring 10-15 mm on CT and a negative FDG-PET result, the post-test probability for N2 disease was only 5%. These patients should be scheduled for thoracotomy because the mediastinoscopy yield will be extremely low.

Staging of Distant Metastases

The detection of distant metastases is of crucial importance, because it usually implies that curative surgical resection of the primary tumor is contraindicated. Metastases occur in about 50% of patients with NSCLC. In patients with clinical or biochemical evidence of disease elsewhere, targeted imaging of those sites is performed. These sites include the brain, which can be examined with CT or MRI, and the skeleton, which can be examined with scintigraphy. Usually, these sites are not imaged in asymptomatic patients with NSCLC.
The probability of metastases is highest for SCLC, which is 60-80% on presentation, and lowest for squamous cell cancers; the incidence increases with advancing stage. No such trend exists for cancer involving the other cell types. Adenocarcinoma tends to metastasize to the brain and adrenals early in its course.

Liver and adrenal metastases

The staging CT scan of the thorax is usually extended to include the liver and adrenal glands. CT scanning has a sensitivity of about 85% in the detection of liver metastases. Similar rates may be obtained with MRI and ultrasonography performed by experienced imagers. Ultrasonography is superior to CT scanning in distinguishing metastases from liver cysts, which account for most of the benign lesions seen on CT scans. (See the images below.)
Liver metastases of lung cancer. A 7-cm metastasis of lung cancer in the right adrenal gland. Sonogram shows a 6-cm right adrenal metastasis of lung cancer. Adrenal metastases are common and often solitary. They must be differentiated from adrenal adenomas, which occur in 1% of the adult population. Lesions smaller than 1 cm are usually benign. Metastases are usually larger than 3 cm; on nonenhanced CT scans, they have an attenuation coefficient of 10 HU or higher. Adenomas and metastases can also be distinguished by using MRI and PET scanning.

Brain metastases

SCLC and adenocarcinoma are the most common sources of cerebral metastases. (See the images below.)
Contrast-enhanced CT scan shows 2 enhancing cerebral metastases of lung cancer in the left cerebral hemisphere. Image obtained in the same patient as in the previous image shows a third cerebral metastasis of lung cancer. MRI is superior to CT, especially in the depiction of the posterior fossa and the area adjacent to the skull base. However, the brain is not routinely imaged in asymptomatic patients with NSCLC, because the incidence of silent cerebral metastases is only 2-4%.

Bone metastases

Technetium-99m (^99m Tc) radionuclide bone scanning (see the images below) is indicated in patients with bone pain or local tenderness. The test has a 95% sensitivity for the detection of metastases but a high false-positive rate because of degenerative disease and trauma. The assessment of these metastases requires comparison of the bone scans with plain radiographs.
Isotope bone scan. Isotope bone scan. Hot spots due to bony metastases in the right second and ninth ribs. Spinal metastases may cause spinal cord compression. Because only about 5% of bony metastases detected with radionuclide scans are asymptomatic, routine preoperative bone scanning is not usually performed.

Lung metastases

Pulmonary metastases (see the image below) from a primary NSCLC are uncommon on presentation, but they are present at autopsy in 20% of cases.
Pulmonary metastases from a primary bronchial neoplasm in the left lower lobe. Accurate preoperative diagnosis of small lung nodules depicted on CT scans is often difficult because they may be indistinguishable from granulomata and fibrotic nodules.

Positron emission tomography scanning

In a study using PET scanning, FDG uptake was increased in 92% of proven adrenal metastases (23 of 25 patients) and was normal in the 8 benign lesions. Whole-body PET will probably decrease the number of adrenal biopsies performed for indeterminate adrenal lesions. In another study, unsuspected distant metastases were found in 11% of patients with primary lung carcinoma.
Whole-body PET scanning is more accurate than thoracic or brain CT scanning, bone scintigraphy, or MRI in staging bronchogenic carcinoma. FDG-PET scan results have prognostic value and are strongly correlated with survival rates in patients who undergo treatment for lung cancer. Patients with positive FDG-PET results have a significantly worse prognosis than patients with negative results. Additionally, FDG-PET may be helpful in guiding treatment.
The introduction of combined PET-CT machines (see the image below) will affect the future workup and treatment of patients with cancer. These machines will also be used in radiation treatment planning. Integrated PET-CT improves the diagnostic accuracy of the staging of non–small-cell lung cancer.
Use of combined positron emission tomography (PET) and computed tomography (CT) in lung cancer staging. The central image is the result of combining the CT (left) and PET (right) images. Courtesy of Rambam Medical Center, Haifa, Israel and GE Medical Systems. In a study by Lardinois et al, integrated PET-CT scanning provided additional information in 20 (41%) of 49 patients beyond that provided by conventional visual correlation of PET and CT.^[12] Tumor staging and node staging were significantly more accurate with integrated PET-CT than with CT alone, PET alone, or visual correlation of PET and CT; in metastasis staging, integrated PET-CT increased the diagnostic certainty in 2 of 8 patients.

Staging of SCLC

SCLC has usually metastasized by the time of presentation. Extensive disease is present in more than 60% of patients. Surgery is an option in fewer than 5% of these patients, who have a small primary and no evidence of spread. Systemic chemotherapy is the main treatment, with response rates of 70% but cure rates of less than 5%.
The distinction between limited and extensive disease is an important staging issue. The TNM system may be applied, but it is not directly relevant to management decisions. The objectives of staging in SCLC are to identify localized disease, for which radiation therapy may be suitable, and to quantify the extent of the disease before therapy.
Localized disease is defined as disease confined to 1 hemithorax that includes ipsilateral, contralateral, and/or supraclavicular nodes. Investigations include chest radiography; CT of the thorax, liver, and adrenal glands; cranial CT; bone scintigraphy; and bone marrow aspiration. The disseminated nature of SCLC makes whole-body survey techniques suitable for its evaluation.^99m Tc-labeled monoclonal antibody fragment NR-LU-10 is used to detect an antigen present in most small cell cancers. Whole-body FDG-PET is a promising technique for detecting nodal disease. Combined MRI of the brain, spine, abdomen, and pelvis enables comprehensive staging with a single modality.

Elbow MRI

MRI Technique

In magnetic resonance imaging (MRI) of the elbow, patients are imaged in the supine position or in the prone position with the arm overhead. Imaging begins about 10 cm above the elbow joint and extends to the bicipital tuberosity. Images are acquired in the axial, coronal, and sagittal planes.^{[1, 2]}
The authors routinely perform axial and coronal T1-weighted (T1W) spin-echo (SE) imaging; axial, coronal, and sagittal fat-suppressed T2-weighted (T2W) SE or short-tau inversion recovery (STIR) imaging (see the images below); and coronal proton density–weighted imaging by 4-mm section thickness with a 0.4-mm intersection gap.
Axial short-tau inversion recovery (STIR) images show hyperintense fluid around the biceps tendon in a patient with a partial tear of the biceps tendon. Coronal short-tau inversion recovery (STIR) images demonstrate a partial tear of the radial collateral ligament. Lateral epicondylitis. Coronal short-tau inversion recovery (STIR) image demonstrates edema near the origin of the common extensor. Intravenous gadolinium-based contrast agent is given to patients with a suspected elbow mass lesion or infection. About 10 mL of a 1:100-250 mixture of contrast agent and saline is injected into the joint if magnetic resonance (MR) arthrography is performed.^[3]
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

Gross Anatomy

Formed by the distal humerus, proximal ulna, and proximal radius, the elbow is a hinge-type synovial joint that provides both stability and function. The distal aspect of the humerus is a wide, flattened structure. The medial third of its articular surface, the trochlea, articulates with the ulna, whereas its lateral capitellum articulates with the radius. A hollow area on the posterior surface of the humerus, above the trochlea, is termed the olecranon fossa. The posterior capsular attachment of the humerus is located above this fossa. (See the images below.)^{[4, 5, 6]}
Coronal short-tau inversion recovery (STIR) image demonstrates a normal ulnar collateral ligament. Coronal short-tau inversion recovery (STIR) image shows a normal radial collateral ligament. LUCL = lateral ulnar collateral ligament, a part of radial collateral ligament. The anterior aspect of the distal humerus contains 2 fossae: the coronoid fossa, located medially, and the radial fossa, located laterally. The anterior capsular attachment to the humerus is located above these fossae.
The proximal end of the ulna contains 2 processes: the olecranon and the coronoid. The olecranon process is posteriorly smooth at the site of attachment of the triceps tendon. The proximal end of the radius consists of a head, a neck, and a tuberosity. The radial head is disk shaped and contains a shallow, cupped articular surface that articulates with the capitellum of the humerus. The radial tuberosity is located beneath the medial aspect of the neck.
A thin, broad, and weak fibrous capsule envelops the entire elbow. The capsule anteriorly extends from its attachment sites above the distal humeral fossae to its distal attachment to the coronoid process and annular ligament. In its posterior portion, the capsule attaches to the capitellum, the olecranon fossa, and the medial epicondyle. At its inferomedial aspect, the capsule attaches to the upper and lateral margins of the olecranon. The lateral part of the capsule is continuous with the superior radioulnar joint. The overlying collateral ligaments strengthen the capsule.
The synovial membrane of the elbow lines the deep surface of the fibrous capsule and the annular ligament. It extends from the articular surface of the humerus, contacting with the olecranon, distal humeral fossae, and medial trochlea surface. A synovial fold projects into the joint between the radius and ulna, partially dividing the articulation into humeroulnar and humeroradial portions.
Several fat pads are located between the fibrous capsule and the synovial membrane. Fat pads are near the synovial fold between the radius and ulna and over the olecranon, coronoid, and radial fossae. These fat pads are extrasynovial but intracapsular. The anterior fat pad, anterior to the distal humerus, normally assumes a teardrop configuration. On lateral elbow radiographs, with the elbow at 90° of flexion, this anterior fat pad is visible. On the contrary, the posterior fat pad, in the olecranon fossa, is normally not visible on lateral radiographs with the elbow in 90° of flexion. However, intra-articular processes that expand the elbow joint (eg, joint effusion) displace these pads.
Radial collateral ligaments and ulnar collateral ligaments (UCLs) reinforce the fibrous capsule.
The radial or lateral collateral ligamentous (LCL) complex consists of the radial collateral ligament, annular ligament, lateral UCL (LUCL), and accessory collateral ligament. The radial collateral ligament attaches superiorly to the lateral epicondyle and inferiorly to the radial notch of the ulna and to the annular ligament.
The ulnar or medial collateral ligament (MCL) is composed of 3 distinct yet continuous bands. The anterior band spans the distance between the medial epicondyle and the coronoid process. The posterior band arises from the posterior aspect of the medial epicondyle to the medial edge of the olecranon process. A thin intermediate band merges with the adjacent bands by virtue of an oblique ray of fibers.
The superior radioulnar joint is located between the radial head and a fibro-osseous ring formed by the annular ligament and the radial notch of the ulna. The radioulnar joint is lined with articular cartilage that is contiguous with the trochlear notch. The radial head is also lined with articular cartilage. The annular ligament anteriorly attaches to the anterior margin of the radial notch. It encircles the head of the radius. At the posterior aspect, it contains several bands that attach to the ulna near the posterior margin of the radial notch.

Tendinous, Ligamentous, and Muscle Abnormalities

Soft-tissue abnormalities involving the tendons, ligaments, and muscles include rupture of the biceps and/or triceps tendons, lateral or medial epicondylitis, injury to the lateral collateral ligament (LCL) or medial collateral ligament (MCL), and posterior dislocation of elbow.
Disruptions of the ligaments about the elbow can accompany severe physical trauma (eg, elbow dislocation),^[7] less-extensive acute trauma (eg, valgus injury),^[8] or chronic stress (eg, pitching a baseball). Injuries to the UCL or MCL predominate.
The ulnar collateral ligament (UCL) or MCL is the primary structure that maintains elbow stability in the presence of valgus stress, though other structures, such as the adjacent flexor musculature, joint capsule, and articular surfaces, contribute to stability. The anterior band of the UCL is functionally the most important for the elbow joint.
On T1W MRIs, findings include increased signal intensity suggesting heterotopic bone formation near the medial epicondyle, epicondylar avulsion, formation of traction osteophytes or subchondral cysts, or sclerosis in capitellum due to lateral injury. On T2W images, findings include increased signal intensity in the anterior band of the MCL, hyperintensity or hypertrophy of the ulnar insertion site (called a sublime tubercle) with or without a full-thickness tear and retraction.
Images of a chronically injured UCL demonstrate laxity, irregularity, and poor definition without increased signal intensity around the ligament. Midsubstance ruptures are most common. Partial detachment of deep undersurface of anterior bundle of UCL should be evaluated by using MR arthrograms, which demonstrate contrast enhancement extending around the corner of sublime tubercle. Images of complete tears show frank extravasation of contrast agent. The differential diagnosis includes medial epicondylitis and a sublime tubercle fracture. (See the image below.)
Coronal T1-weighted (T1W) images show a partial tear of the ulnar collateral ligament. LCL injury is less common than MCL injury. LCL injury is usually the result of chronic trauma, and it is associated with tennis elbow. LUCL injury is most important, as it results in posterolateral rotatory insufficiency. Laxity can occur after extensive subperiosteal elevation of the extensor tendons in cases of tennis elbow. On T1W images, a tear of the LUCL ligament may be seen at its humeral origin, and on T2W images, disruption of ligamentous fibers with fluid signal intensity may be seen. Associated findings include fractures of coronoid process, radial head, or capitellum and dislocation of the radius or ulna.

Avulsions and tears

Avulsions and tears of tendons about the elbow are uncommon. Avulsion at sites of tendinous attachment may occur as a complication of systemic diseases, such as primary and secondary hyperparathyroidism, systemic lupus erythematosus, rheumatoid arthritis, and osteogenesis imperfecta. They may also occur as a consequence of physical injury. Tears of the tendon can be graded as follows: grade I is mild strain and/or tendinosis, grade II is partial tear, and grade III is complete disruption.
Discontinuity and retraction of the tendon accompany complete tears, whereas remaining intact tendinous fibers accompany partial tears. Alterations in signal intensity depend on the age of the injury. On proton density–weighted images, tendinosis is seen as increased signal intensity in a thickened tendon. On T2W MRIs, increased signal intensity similar to that of fluid without discontinuity of the tendon suggests partial tear. Full-thickness tears with or without retraction of the ends of the tendon indicate a complete tear. Sagittal fat-suppressed T2W images are particularly useful in identifying tendon retraction in injuries of the biceps and triceps tendons. (See the images below.)
Axial short-tau inversion recovery (STIR) images show hyperintense fluid around the biceps tendon in a patient with a partial tear of the biceps tendon. Sagittal short-tau inversion recovery (STIR) images demonstrate a complete tear and avulsion of the biceps tendon. Although rupture of the distal portion of the tendon of the biceps brachii muscle accounts for only 5% of all biceps injuries, they are an important injury about the elbow. The typical mechanism is related to forceful hyperextension applied to a flexed and supinated forearm. Complete rupture, with avulsion of the tendinous attachment to the radial tuberosity, generally occurs in men older than 40 years and in the dominant extremity.
Associated findings are a fluid-filled bicipital bursa and tendon sheath, a hypointense and thickened tendon on T1W images, and hypertrophy of the radial tuberosity. Lateral epicondylitis is sometimes present.^[9] An important differential diagnosis is bicipital radial bursitis, which results in fluid in the bicipital bursa with normal signal intensity in the adjacent tendon. An absence of signal-intensity changes on T2W and STIR images with an atrophic or hypertrophic tendon indicate a chronic tear.

Triceps tendon injuries

Regarding injuries of the triceps tendon, the typical patient is a middle-aged man who had forced flexion of an extended forearm as in a motorcycle accident or sports-related trauma. Most tears occur at the insertion site at the olecranon process.^[10] Avulsion of the tendo-osseous attachment may be observed. Myotendinous ruptures are uncommon. Other associated abnormalities are olecranon bursitis and radial-head fractures. The differential diagnosis includes olecranon bursitis, which may be associated with infection and in which the underlying tendon appears normal; hematoma of the triceps muscle, where the muscle appears hyperintense on T1W and T2W images; and fracture of the olecranon, which commonly occur in adolescent due to direct trauma or a throwing injury. (See the image below.)
Axial T1- and sagittal T2-weighted fat-saturated images show a sprain of the triceps muscle and tendinosis.

Medial epicondylitis

Medial epicondylitis is also known as golfer's elbow or medial tennis elbow. This injury is due to chronic overload and overuse of flexor pronator muscle group. It involves the interface between the origins of the pronator teres and the flexor carpi radialis. Coronal fat-suppressed T2W images demonstrate hyperintensity of the origin of flexor pronator.

Lateral epicondylitis

Lateral epicondylitis, or tennis elbow, is 7-20 times more common than medial epicondylitis. This injury is characterized by degeneration and partial tears of the extensor group of tendons. Partial avulsion of the radial collateral ligament and the posterior elbow dislocation may also be present. Hyperintensity is seen on fat-suppressed T2W or STIR images in the origin of the common extensor. Associated periostitis, increased signal intensity in the anconeus muscle, and soft-tissue edema may be seen. (See the images below.)
Coronal short-tau inversion recovery (STIR) images demonstrate a partial tear of the radial collateral ligament. Lateral epicondylitis. Coronal short-tau inversion recovery (STIR) image demonstrates edema near the origin of the common extensor.

Neuropathies Around The Elbow Joint

Entrapment and compression neuropathies about the elbow may involve the ulnar, radial, or median nerve.

Ulnar nerve

Neuropathies involving the ulnar nerve are the most common. Entrapment of the ulnar nerve in the fibro-osseous tunnel posterior to the medial epicondyle of the humerus results in the cubital tunnel syndrome. Typical causes of this syndrome are injury and progressive cubitus valgus deformity (tardy ulnar nerve palsy). Other causes are osteoarthritis, rheumatoid arthritis, nerve subluxation, prolonged bedrest, anomalous muscles, thickened cubital tunnel retinaculum (Osborne ligament), malunion or nonunion of a condylar fracture, masses, and trochlear hypoplasia.
MRI abnormalities include displacement or shift of the ulnar nerve, a soft tissue mass, and thickening and increased signal intensity in the compressed nerve. Ulnar-nerve enlargement may be focal, occurring at the level of the cubital tunnel, with normal girth noted proximal and distal to the tunnel. On fat-suppressed T2W images, neurogenic edema can be seen in muscles the ulnar nerve supplies. A thickened cubital tunnel retinaculum may be demonstrated. The differential diagnosis includes enlarged perineural veins, which due to increased venous pressure are seen as flow voids on T2W images.

Radial nerve

Entrapment of a portion of the radial nerve may occur just distal to the elbow, where the posterior interosseous, or deep, branch passes into the supinator muscle (arcade of Frohse). Individuals in occupations that require frequent supination and pronation are susceptible to this injury. Causes of supinator syndrome are elbow dislocations, fractures, rheumatoid arthritis, soft tissue tumors, and traumatic or developmental fibrous bands. On fat-suppressed T2W images, findings include diffuse increased signal intensity in all or some muscles the posterior interosseus nerve supplies; this finding suggests denervation. Reduced size of the muscle belly and fatty atrophy may be seen. The differential diagnosis includes nonspecific myositis; T2W images may show hyperintensity in the muscle, which is related to trauma.

Median nerve

Median-nerve entrapment can occur due to hypertrophy of the pronator teres muscle or fibrous bands leading to compression of the nerve in the antecubital area where the nerve passes between the 2 heads of the pronator teres muscle under the edge of the flexor digitorum sublimis muscle (pronator syndrome). This syndrome results in sensory symptoms as opposed to anterior interosseus nerve (AIN) syndrome, which involves denervation of flexor pollicis longus and flexor digitorum profundus to second and third digits. T2W and STIR images demonstrate diffuse increase signal intensity in affected muscles, with decreased muscle bulk suggesting denervation. Fatty atrophy is best demonstrated on T1W images.
In cases of compression of the radial or median nerve, MRI may reveal a mass (eg, lipoma, ganglion cyst) and displacement and abnormal signal intensity in the affected nerve.

Bone Abnormalities

Osteochondritis dissecans

Osteochondritis dissecans about the elbow usually affects the capitulum in boys and male adolescents aged 12-16 years. This disorder differs from a developmental alteration (osteochondrosis) of the capitellar ossification center known as Panner disease, which affects children aged 5-11 years. The latter disease process affects the whole capitellum, and loose body formation and residual deformity is usually absent in Panner disease. (See the image below.)
Coronal short-tau inversion recovery (STIR) images demonstrate osteochondritis dissecans with adjoining marrow edema in the capitulum. The precise relationship of osteochondritis dissecans of the capitulum and an osteochondral fracture is not clear, but most investigators regard the former as a posttraumatic abnormality that may lead to osteonecrosis. MRI of osteochondritis dissecans of the capitulum may be performed to gain information about the integrity of the adjacent articular cartilage, the viability of the separated fragment, and the presence of associated intra-articular osseous and cartilaginous bodies. Variable signal intensity may be seen in the fragment depending on the degree of sclerosis. Cystic changes may be seen. T1W images may show increased signal intensity in the fragment, as opposed to normal marrow fat intensity and hypointensity around the fragment. Joint fluid or granulation tissue at the interface between the fragment and the parent bone manifests as increased signal intensity on T2W MRIs and generally indicates an unstable lesion.
Iwasaki et al studied 10 young male athletes with advanced lesions of capitellar osteochondritis dissecans to determine whether MRI findings improve with increasing time after mosaicplasty. The authors found that at 12 months, all patients were able to return to their competitive level of sports. Fluid surrounding the graft was found in all patients at 3 months and in 4 patients at 6 months. At 12 months, the grafts were all well seated within the recipient sites, with no MRI evidence of graft loosening. The overall MRI scores significantly improved from 3 to 12 months. The MRI findings therefore indicated that the graft incorporation to the surrounding tissues occurred around or after 6 months after surgery, suggesting that rehabilitation precautions be taken for up to 6 months after mosaicplasty for young athletes with capitellar OCD.^[1]
Han et al evaluated the distribution of shoulder and elbow injuries confirmed by MRI in 554 throwing athletes and found that there is significant difference in the distribution of injuries according to the player's age and position. Junior high school players sustained a higher proportion of osteochondritis dissecans than players in high school and college, and the players in junior high school with UCL injuries were taller and heavier than the players in the control group. High school and college players were more likely to have UCL injuries or SLAP lesions, and in the high school group with UCL injuries or SLAP lesions, the players were both taller and heavier than the players in the control group. Pitchers and outfielders were more likely to have UCL injuries than infielders.^[11]
A potential pitfall is a pseudodefect of the capitulum, which is seen as abrupt slope of posterior portion of capitellum that is not associated with any marrow edema in the adjacent bone. Osteochondritis dissecans also occurs on the anterior surface.

Occult fractures

Radiographically occult fracture can be imaged by using MRI, which demonstrates bone-marrow edema with or without a hypointense linear fracture line. Occult fractures are most commonly seen in the region of the radial head in adults and in the supracondylar region in children.
A fracture of the coronoid process is due to bony avulsion of the brachialis insertion, and posterior dislocation of the ulna and an olecranal fracture due to direct trauma or forced flexion on an extended forearm may be seen.
Fractures of the lateral condyle result from avulsion injury due to the forearm extensor and supinator muscles, fractures involving the medial condyle result from an avulsion injury due to contraction of the forearm flexor muscles.

Osteomyelitis

Osteomyelitis is commonly seen as an acute process in children and as a chronic process in adults. It is often the result of adjacent infectious bursitis. Staphylococcus aureus is the most common infecting organism in all age groups.
MRI findings include bone-marrow edema, which appears hypointense on T1W images and hyperintense on T2W images; interosseus abscess, which appears hyperintense on T2W images; cortical destruction; cloaca, which appears as focal hyperintensity in a hypointense periosteum on T2W images; a Brodie abscess, which appears as focal hyperintensity surrounded by a hypointense sclerotic rim; and cellulitis, myositis, bursitis, and involvement of the sinus tracts. Contrast-enhanced T1W images may show enhancing bone marrow and peripheral enhancement in the abscess.

Synovial Abnormalities

Synovial proliferation in the elbow may accompany a variety of disease processes, including rheumatoid arthritis, septic arthritis, crystal deposition disorders, pigmented villonodular synovitis, and idiopathic synovial osteochondromatosis.

Inflammatory disorders

Rheumatoid arthritis and other synovial inflammatory disorders affecting the elbow lead to proliferation and thickening of the synovial membrane and accumulation of joint fluid. The signal-intensity characteristics of the abnormal synovium and fluid are similar on MRIs obtained with standard sequences. Erosions may be seen as hyperintense defects in the subchondral bone at the joint edges (bare areas). The intravenous administration of gadolinium compounds enhances the signal intensity of the inflammatory tissue and does not affect the signal intensity of fluid on MRIs obtained immediately after their injection.
Synovial inflammation and fluid accumulation in the olecranon bursa is seen after injury and in cases of rheumatoid arthritis, septic bursitis, and gout and other diseases involving crystal deposition. The diagnosis of olecranon bursitis is generally apparent on physical examination. A sympathetic effusion in the elbow joint may accompany this condition. In rheumatoid arthritis, subcutaneous nodules may simulate the appearance of olecranon bursitis.
Para-articular synovial cysts that communicate with the elbow joint are a recognized manifestation of rheumatoid arthritis. However, theoretically, they could occur with any process leading to elevation of intra-articular pressure in the elbow. A valvelike mechanism may be present between the synovial cyst and the elbow joint. Such cysts predominate in the antecubital region.

Pigmented villonodular synovitis

Pigmented villonodular synovitis may involve the elbow, initially leading to an effusion and subsequently leading to osteoporosis and even joint-space loss and bone erosions. Although an appropriate clinical history and typical radiographic abnormalities may suggest the diagnosis, the deposition of hemosiderin in the affected synovial tissue produces regions of persistent hypointensity on T2W images, especially, gradient-echo MRIs. This finding also may be observed in cases of chronic hemarthrosis, hemophilia, and synovial hemangioma.

Idiopathic synovial osteochondromatosis

Idiopathic synovial osteochondromatosis, which is related to metaplasia of the synovial lining, is accompanied by synovial proliferation and the formation of intrasynovial nodules of cartilage. The fate of these nodules varies, though they may become calcified or ossified. They may become free within the joint cavity and later become embedded in a distant synovial site. Routine radiography is sensitive to calcified and ossified intra-articular bodies, but it is insensitive to nonossified bodies. Arthrography, in which the loose bodies appear as multiple filling defects within the opacified joint, and MRI can be helpful in diagnosing this condition.

Loose bodies

Intra-articular and osteocartilaginous loose bodies can result from any process leading to disintegration of the articular surface of the elbow joint. Although trauma is the most important cause, other etiologies include osteoarthritis, synovial osteochondromatosis, and calcium pyrophosphate deposition disease (CPPD). In common with intra-articular bodies in other locations, bodies originating from the joint surface may be composed of cartilage alone, cartilage and bone together, or (in rare cases) bone alone.

Bursitis and Other Soft Tissue Masses Around Elbow Joint

Bicipitoradial bursitis and interosseous bursitis can affect the insertion of the biceps tendon, as well as flexion and supination of forearm. They typically occur in men after athletic activity and manifest as a painful antecubital soft-tissue mass with painful flexion. Findings on MRI include a cystic mass interposed between the distal biceps tendon and the anterior aspect of the radial tuberosity. Sometimes, communication with the elbow joint below the annular ligament may be demonstrated.
Olecranal bursitis occurs in an adolescent or adult patient and appears as a fluid collection posterior to the insertion of the triceps tendon.
MRIs may show soft tissue tumors around the elbow. Some of the tumors may have typical patterns of signal intensity: Lipomas may have fat intensity; liposarcomas, variable signal intensity with or without fat intensity; ganglion cysts, fluid intensity; fibromas, dark on T1W and T2W images; and hemangiomas, flow voids and/or phleboliths. However, most tumors have variable signal intensity and gadolinium contrast enhancement. Although these findings help in the delineation of tumors, they may not accurately define their margins and the extent of malignancy.

Brachial Plexus Evaluation with MRI

Overview

Evaluation of the brachial plexus is a clinical challenge. Physical examination has traditionally been a mainstay in evaluating and localizing pathology involving the brachial plexus. Physical examination is especially difficult in patients with scarring and fibrosis secondary to surgery or irradiation. Electrophysiologic studies can be used to detect abnormalities in nerve conduction, but they are poor for localizing a lesion.^{[1, 2]} (See the diagram below.)
Diagram of the brachial plexus. Injury to the brachial plexus is associated with weakness and paresthesias of the upper extremity on the affected side. Thorough neurologic examination can be performed to localize the injury and to help the radiologist pinpoint the location of pathology.
As the technology and resolution have improved, magnetic resonance imaging (MRI) has become increasingly important in the evaluation of brachial plexus pathology. Correlation of imaging results with electrophysiologic findings increases overall specificity and sensitivity.^{[3, 4, 5]}
According to Nardin et al,^{[2, 6]} electromyelography (EMG) and MRI examinations are complementary. Their study demonstrated that the sensitivity of EMG and MRI were 72% and 60%, respectively. Plain radiography can depict large lesions affecting the brachial plexus. However, radiographs are far less sensitive than other studies. Computed tomography (CT) scanning has increased sensitivity for depicting extrinsic masses that compress the nerves; however, it offers poor soft tissue contrast for direct evaluation of the nerves.
With the advent of MRI, nerves that compose the brachial plexus can now be directly evaluated. Intrinsic and extrinsic pathology can be evaluated. Exact anatomic components of the brachial plexus, such as the roots, trunks, divisions, and cords, can be identified. MRI has the additional benefit of multiplanar imaging and increased soft tissue contrast. The tissue resolution of MRI is constantly improving with new pulse sequences and coil designs.^{[1, 6, 7, 8, 9, 10, 11]} (See the images below.)
Birth trauma. Sagittal image of the brachial plexus shows an area of increased signal intensity in the C6 neural foramen. This is an area of particular concern in cases of birth trauma, and the finding is consistent with traumatic injury of the nerve root. Birth trauma. Coronal image of the brachial plexus shows an area of increased signal intensity in the right C6 neural foramen. Birth trauma. With radiography and CT scanning, changes in the shape or position of the brachial plexus have been used to assess pathology.^[12] With MRI, the nerve can be directly visualized and evaluated for pathology. MRI sequences such as fat-saturated T2-weighted spin-echo, short-tau inversion recovery (STIR), and gadolinium-enhanced T1-weighted spin-echo sequences help in depicting subtle changes in the signal intensity of the nerves or enhancement and aid in refining the differential diagnosis. In addition, maximum intensity projections can make localization and visualization of the pathology most understandable for referring clinicians and surgeons. (See the images below.)
Avulsion in a 17-year-old female adolescent after she was ejected from an automobile in a collision. Oblique cervical myelogram shows extravasation of contrast material from torn right lower nerve-root sheaths. Avulsion in a 17-year-old female adolescent after she was ejected from an automobile in a collision. Axial image obtained with a long repetition time (TR) and a long echo time (TE) (TR/TE, 3800/98 ms) shows extensive injuries to the right paraspinal soft tissues. The 3 images immediately following this one were obtained 3 months after this image was produced. Avulsion in a 17-year-old female adolescent after she was ejected from an automobile in a collision. Coronal image obtained with a long repetition time (TR) and long echo time (TE) (TR/TE, 1800/71 ms) shows circumscribed right paravertebral fluid collections at C6-7 and C7-T1. These represent pseudomeningoceles from torn nerve-root sheaths and avulsed nerve roots. Avulsion in a 17-year-old female adolescent after she was ejected from an automobile in a collision. Sagittal image obtained with a long repetition time (TR) and long echo time (TE) (TR/TE, 1800/112 ms) shows circumscribed right paravertebral fluid collections at C6-7 and C7-T1. These represent pseudomeningoceles from torn nerve-root sheaths and avulsed nerve roots. Avulsion in a 17-year-old female adolescent after she was ejected from an automobile in a collision. Axial image obtained with a long repetition time (TR) and long echo time TE (TR/TE, 4000/100 ms) shows circumscribed right paravertebral fluid collections at C6-7 and C7-T1. These represent pseudomeningoceles from torn nerve root sheaths and avulsed nerve roots. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see Medscape.

Technique and Imaging Parameters

The brachial plexus can be easily identified on MRI by first identifying the anterior scalene muscle. The brachial plexus and subclavian artery (relationship outlined above) are deep to the anterior scalene. Normal components of the brachial plexus have low signal intensity on images obtained with all sequences and are surrounded by fat. The roots are best seen on axial images, whereas the remaining components are well seen on coronal and sagittal images.^{[7, 13, 14]} (See the images below.)
Non-Hodgkin lymphoma in a 58-year-old man. Coronal spoiled gradient-echo image (repetition time [TR]/echo time [TE], 175/4.2 ms; flip angle, 90°) shows lymphomatous lesions in the right brachial plexus and in the marrow of the humerus. Non-Hodgkin lymphoma. Axial image obtained with a short repetition time (TR) and short echo time (TE) (TR/TE, 550/9 ms) shows lymphomatous lesions in the right brachial plexus and in the marrow of the humerus. Non-Hodgkin lymphoma in a 58-year-old man. Sagittal images obtained with a short repetition time (TR) and a short echo time (TE) (TR/TE, 650/9 ms) show lymphomatous lesions in the right brachial plexus and in the marrow of the humerus.

Radiofrequency coil

A surface coil provides resolution higher than that of a body coil, but it increases artifact due to respiratory motion. A combination of each may be used in sequences for the brachial plexus. As such, the surface coil is used for the spinal cord and exiting spinal nerve roots, whereas the body coil is used to image the plexus lateral to the interscalene triangle.

Field of view

Examination of the brachial plexus begins with the roots and trucks in the proximal aspects within the supraclavicular region and continues to the origin of the terminal branches at the lateral margin of the pectoralis minor muscle in the infraclavicular region.
The field of view (FOV) is 17-22 cm for the direct coronal orientation and 14-17 cm for sagittal or oblique sagittal orientations.

Matrix

A matrix of 512 X 256 or 512 X 512 is used.

Section thickness

The recommended section thickness is 4 mm with an intersection gap of 0-0.5 mm for direct coronal imaging and 4 mm with an intersection gap of 1-2 mm for sagittal or oblique sagittal imaging. If axial images are obtained, 4-mm thickness with a 1- to 1.5-mm intersection gap may be performed.

Orientation

Images should be obtained in 2 planes. Direct coronal plane imaging is preferred over oblique coronal imaging because the brachial plexus has a shallow obliquity relative to the true coronal plane and because it can be imaged on 1 or 2 coronal sections.
Cross-sectional imaging of the nerve components of the plexus may be performed by using either the true sagittal or the oblique sagittal plane on the side of interest. True sagittal imaging allows for comparison with the standard cross-sectional anatomy, which some find helpful in the recognition of appropriate anatomic landmarks. However, oblique sagittal imaging represents the true cross-section of the plexus more accurately than true sagittal imaging and thus allows for increased sensitivity to pathology, including changes in caliber, alteration in signal intensity, or presence of a fascicular pattern to the nerve components.
Some institutions include a contrast-enhanced T1-weighted axial sequence as part of their routine evaluation of the brachial plexus.
Avulsion in a 15-year-old male adolescent with palsy of the right upper extremity due to trauma related to a snowmobile accident. Coronal image obtain with a short repetition time (TR) and a short echo time (TE) (TR/TE, 600/8 ms) shows a poorly defined zone of low signal intensity in the region of the right brachial plexus. Avulsion in a 15-year-old male adolescent with palsy of the right upper extremity due to trauma related to a snowmobile accident. Coronal image obtained with a long repetition time (TR) and a long echo time (TE) (TR/TE, 7058/98 ms) shows a traumatic fluid collection containing several retracted nerves of the right brachial plexus. Avulsion in a 15-year-old male adolescent with palsy of the right upper extremity due to trauma related to a snowmobile accident. Sagittal image obtained a long repetition time (TR) and long echo time (TE) (TR/TE, 10,588/98 ms) shows a traumatic fluid collection containing several retracted nerves of the right brachial plexus. Clavicular fracture in a 57-year-old man with a traumatic comminuted fracture of the left clavicle. Coronal image obtained with a short repetition time (TR) and a short echo time (TE) (TR/TE, 600/9 ms) shows the fracture mildly impressing on the left brachial plexus. Clavicular fracture in a 57-year-old man with a traumatic comminuted fracture of the left clavicle. Sagittal image obtained with a long repetition time (TR) and long echo time (TE) (TR/TE, 2000/83 ms) shows the fracture mildly impressing on the left brachial plexus. Lipoma in a 38-year-old woman with a lipoma above the left brachial plexus. Coronal image obtained with a short repetition time (TR) and short echo time (TE) (TR/TE, 600/9 ms) shows a lipoma mildly impressing on the left brachial plexus. Lipoma in a 38-year-old woman with a lipoma above the left brachial plexus. Sagittal image obtained with a short repetition time (TR) and short echo time (TE) (TR/TE, 600/9 ms) shows a lipoma mildly impressing on the left brachial plexus. Neurofibromatosis type 1 in a 26-year-old woman. Coronal images obtained with a short repetition time (TR) and a short echo time (TE) (TR/TE 650/16 ms) show several circumscribed neurofibromas along the right brachial plexus. Neurofibromatosis type 1 in a 26-year-old woman. Coronal fat-suppressed images obtained with a long repetition time (TR) and a long echo time (TE) (TR/TE, 4000/96 ms) show several circumscribed neurofibromas along the right brachial plexus. The neurofibromas have high signal intensity. Postirradiation changes in an 84-year-old woman with a history of breast cancer. Coronal image obtained with a short repetition time (TR) and short echo time (TE) (TR/TE, 400/9 ms) shows irregular thickening of the left brachial plexus. Postirradiation changes in an 84-year-old with a history of breast cancer. Coronal contrast-enhanced fat-suppressed image obtained with a short repetition time (TR) and a short echo time (TE) (TR/TE, 650/9 ms) shows poorly defined zones of contrast enhancement in the region of the brachial plexus. These zones representing radiation-induced changes to infiltrating tumor.

Pulse sequences

T1- and T2-weighted images are obtained with identical parameters in terms of FOV, matrix, section thickness, and imaging plane.
STIR or frequency-selective fat-saturation methods may be used for T2-weighted MRI to increase the conspicuity of abnormal signal intensity from the signal intensity of adjacent fat. Each has its advantages and disadvantages. STIR has been described as being more reliable than the other method because of its uniform and consistent fat suppression and excellent T2-like contrast when long repetition times are used.
The STIR method has several disadvantages. For example, it has a relatively low signal-to-noise ratio, it offers relatively low tissue contrast, and it is more susceptible to flow artifacts than other methods.
In contrast, frequency-selective fat-saturation methods have the advantage of an improved signal-to-noise ratio, T1-weighted imaging, and reduced flow-related artifacts. The major disadvantage of this type of fat suppression is the nonuniformity of fat suppression with the FOV primarily from inhomogeneity of B₀. This variability in fat suppression is exacerbated by the nonuniformity in B₁.
When radiation injury, neoplasm, infection, or inflammatory etiologies are present or suspected, contrast-enhanced fat-suppressed T1-weighted MRI should be performed. The suggested protocol is summarized in in the image below.
Summary of suggested MRI techniques. FOV = field of view; T1WI = T1-weighted imaging; STIR = short-tau inversion recovery; FS = fast spin echo.