Aim of the work
To evaluate the role of magnetic resonance imaging (MRI) in preoperative assessment of ano-rectal fistula and tracing its full extent and relationship.
Materials and methods
Twenty-four patients with ano-rectal fistula were enrolled in this study. They were examined with different MRI sequences for evaluation of the fistulas and their extent. Fistulas were classified according to St. James’s University Hospital MRI based classification system (which correlates the Parks surgical classification to anatomic MRI findings) into 5 grades. Then, interrelation between surgical and MRI findings was statistically analyzed with evaluation of the accuracy of each MRI sequence used.
Grade 1 was the most frequent (37.5%) type of ano-rectal fistula. The most common location of the internal opening of the fistula was at 6 o’clock position. Combination of oblique coronal and axial planes of contrast-enhanced fat suppressed T1-weighed fast spin-echo (CE FS T1WFSE) sequence images showed the highest accuracy (99.4%) in diagnosis of ano-rectal fistula.
MRI is a useful imaging tool in the preoperative assessment of ano-rectal fistula. A significant accordance between surgical and MRI findings was achieved by using combination of coronal and axial planes of CE FS T1WFSE sequence images.
After completing this journal-based SA-CME activity, participants will be able to:
■ Describe the anatomy of the ampulla and periampullary region.
■ Discuss the primary imaging modalities used for evaluation of the ampulla and periampullary region.
■ Describe the imaging features of various ampullary and periampullary lesions.
The ampulla of Vater is located in the major duodenal papilla and represents the junction of the common bile duct (CBD) and main pancreatic duct of Wirsung (Fig 1).
The joining of the CBD and main pancreatic duct may occur in three ways. Most commonly (60%), the CBD and main pancreatic duct join to form a common channel that is 1–8 mm in length. Less often (38%), a common channel is not present, and instead there is a single orifice in the papilla that contains a separate opening for each duct (double-barrel configuration). Rarely (2%), there are two separate orifices in the papilla that drain the CBD and main pancreatic duct separately (1).
The major duodenal papilla is located along the second or third portion of the duodenum (2). At cross-sectional imaging, the major duodenal papilla normally is 1 cm or less in diameter. On contrast material–enhanced images, its enhancement is similar to that of the adjacent duodenal mucosa (2,3).
Given the importance of these anatomic structures, it is essential for radiologists to understand the variety of lesions that can occur in the ampulla and periampullary region (Table).
Symptoms, Imaging Findings, and Diagnosis of Ampullary and Periampullary LesionsClick image to enlarge
Approximately 62% of lesions manifest at imaging as a discrete nodular mass that produces an irregular filling defect at the distal margin of the pancreaticobiliary junction (2). However, in some cases, a discrete tumor in the ampullary area may not be visible at imaging (5). At non–contrast-enhanced CT, the tumor typically appears as a hypoattenuating mass with an attenuation of approximately 40 HU. The tumor usually demonstrates enhancement on arterial and portal venous phase images (6). Its borders may be lobulated or infiltrating (Fig 2). At MR imaging, a visible ampullary tumor will enhance after gadolinium-based contrast agent administration (7). The addition of diffusion-weighted imaging sequences to conventional MR imaging has more recently been shown to improve detection of ampullary carcinoma (5). At MRCP, ampullary tumors typically manifest as a filling defect or focal stricture at the distal end of a dilated CBD (7). Dilatation of both the biliary and pancreatic ducts is seen in approximately 52% of cases (2). If the mass does not fully obstruct the biliary and pancreatic ducts after their junction, or when there are separate duodenal openings for the biliary and pancreatic ducts, the double-duct sign may be absent (2). In cases where duct dilatation is seen at imaging without a visible mass, the tumor may not be evident even at endoscopy, and diagnosis may require papillotomy and deep biopsy.
Ampullary adenomas are uncommon premalignant lesions that may undergo malignant transformation into adenocarcinoma. They may occur spontaneously or in the context of familial polyposis syndrome (8). The prevalence of ampullary adenomas has been estimated as 0.04%–0.12% in autopsy series (9). Cross-sectional imaging findings of ampullary adenomas (Fig 3) have not been described extensively. In one study, common CT findings of an ampullary adenoma included an ampullary soft-tissue mass greater than 1 cm, an irregular margin of the ampulla, extrahepatic biliary duct dilatation, and pancreatic duct dilatation (10). At imaging, the tumors are more readily visualized when the duodenum is well distended.
A cholangiocarcinoma is an adenocarcinoma that arises from the epithelial cells of the biliary duct. The reported age-adjusted incidence of extrahepatic cholangiocarcinoma is 1.2 per 100,000 men and 0.8 per 100,000 women (11). There are two gross subtypes of extrahepatic cholangiocarcinoma: infiltrating and polypoid. A common imaging feature of both subtypes is biliary duct dilatation, which terminates abruptly at the level of the mass (12). At cross-sectional imaging, an infiltrating cholangiocarcinoma is typically characterized by ductal wall thickening and sudden luminal obliteration (2). A polypoid lesion may manifest at imaging as an intraductal polypoid mass that typically does not cause complete obstruction (Fig 4) (2). A cholangiocarcinoma typically is hypointense relative to the liver parenchyma on T1-weighted MR images and hyperintense on T2-weighted MR images (13). It may also demonstrate homogeneous slow enhancement and typically is more conspicuous on fat-suppressed MR images (13).
A periampullary duodenal adenocarcinoma is a rare tumor that typically abuts but spares or only partially involves the major duodenal papilla (7). At imaging, the tumor manifests as either a polypoid or intraluminal mass, with eccentric duodenal wall thickening (14,15). Between 1985 and 2005, 67,843 patients in the United States were diagnosed with small-bowel malignancies, with adenocarcinoma accounting for 37% of these cases (16). However, the true incidence of periampullary duodenal adenocarcinoma is not known. Duodenal adenocarcinoma more commonly involves a relatively short segment of the bowel and results in gradual luminal narrowing (17). If there is ampullary involvement, biliary dilatation may be seen at imaging. Larger lesions may cause luminal obstruction and gastric distention. At multiphasic CT studies, periampullary duodenal adenocarcinoma is typically hypovascular (Fig 5) (17). At MR imaging, the lesions manifest as polypoid fungating masses or areas of eccentric wall thickening (2).
PNETs constitute a rare subtype of tumors that arise from the endocrine cells in or near the pancreas (26). A conservative estimate of the incidence of PNETs in the United States is approximately 25–30 per 100,000 individuals (27). The most common location for these tumors is the gastrinoma triangle, which is defined by the junction of the cystic and common hepatic ducts, the junction of the second and third portions of the duodenum, and the border of the body and tail of the pancreas (26). PNETs are unlikely to cause ampullary or ductal obstruction. They are hypoattenuating on nonenhanced CT images (28). At MR imaging, they typically are hypointense on fat-suppressed T1-weighted images and hyperintense on T2-weighted images (12,29). At contrast-enhanced CT or MR imaging, PNETs demonstrate homogeneous hyperenhancement relative to the normal pancreatic parenchyma during the arterial and capillary phases (Fig 9) (12,30).
Figure 9b PNET in a 42-year-old woman. (a) Coronal T2-weighted HASTE MR image shows a round mass (arrow) in the pancreatic head adjacent to the ampulla, with dilatation of the CBD. (b)