Mimics, Miscalls, and Misses in Pancreatic Disease Koenraad J

Mimics, Miscalls, and Misses in Pancreatic Disease Koenraad J. Mortelé1 The radiologist plays a pivotal role in the detection and This chapter will summarize, review, and illustrate the characterization of pancreatic disorders. Unfortunately, the most common and important mimics, miscalls, and misses in accuracy of rendered diagnoses is not infrequently plagued by pancreatic imaging and thereby improve diagnostic accuracy a combination of “overcalls” of normal pancreatic anomalies of diagnoses rendered when interpreting radiologic studies of and variants; “miscalls” of specific and sometimes pathog- the pancreas. nomonic pancreatic entities; and “misses” of subtle, uncom- mon, or inadequately imaged pancreatic abnormalities. Ba- Normal Pancreatic Anatomy sic understanding of the normal and variant anatomy of the The Gland pancreas, knowledge of state-of-the-art pancreatic imaging The coarsely lobulated pancreas, typically measuring ap- techniques, and familiarity with the most commonly made mis- proximately 15–20 cm in length, is located in the retroperito- diagnoses and misses in pancreatic imaging is mandatory to neal anterior pararenal space and can be divided in four parts: avoid this group of errors. head and uncinate process, neck, body, and tail [4]. The head, neck, and body are retroperitoneal in location whereas the Mimics of pancreatic disease, caused by developmental tail extends into the peritoneal space. The pancreatic head is variants and anomalies, are commonly encountered on imag- defined as being to the right of the superior mesenteric vein ing studies [1–3]. To differentiate these benign “nontouch” en- (SMV). The uncinate process is the prolongation of the medi- tities from true pancreatic conditions, radiologists should be al and caudal parts of the head; it has a triangular shape with a familiar with them, the imaging techniques available to study straight or concave anteromedial border. The pancreatic neck them, and their variable imaging presentations [1–3]. Classic is located to the left of the head and ventral to the SMV. The examples include pseudomasses due to fetal lobulations, aber- pancreatic body and tail are situated behind the stomach, and rant ductal configurations, pancreatic clefts, and intrapancre- the distinction between them is not clearly defined but can be atic accessory spleens. determined using half of the distance between the neck and Miscalls of pancreatic abnormalities are generally multi- the end of the pancreatic tail [4]. There is a gradual decrease factorial and may be induced by lack of individual or general- of the size of the pancreas with age [5]. Moreover, the size of ized knowledge, inadequate imaging technique, and inaccu- the pancreas is variable. Therefore, overall proportions and rate interpretation due to overlapping or confusing features of features of the gland (including lobular architecture, symme- certain entities [1]. Classic examples include misdiagnosis of try, density and signal intensity, enhancement, normal duct, uneven pancreatic lipomatosis, determination of pancreatic and contour) are considered more important than absolute cancer resectability, characterization and accurate measure- measurements in assessing the presence of a focal or diffuse ment of cystic pancreatic lesions, and the misdiagnosis of pancreatic abnormality. autoimmune pancreatitis and inflammatory pseudotumors in chronic pancreatitis. The Ducts Misses of pancreatic disorders on imaging can typically The normal anteroposterior diameter of the main pancre- be classified as perceptual, technical, and communication re- atic duct measures maximally 3.5 mm in the head, 2.5 mm lated [1]. Classic examples include failed detection of small in the body, and 1.5 mm in the tail [2]. The main pancreatic (resectable) pancreatic cancers and subtle unresectable pancre- duct (MPD) receives approximately 20–30 side branches that atic malignancies, hypervascular pancreatic neoplasms, early enter the duct at right angles [6]. There are approximately 27 chronic pancreatitis, vascular complications in acute pancre- different normal ductal configurations, including the common atitis, and adenocarcinomas complicating intraductal papillary sigmoid configuration and the rare looped configuration. The mucinous tumor (IPMN). downstream ductal configuration most commonly (60%) en- 1Department of Radiology, Divisions of Abdominal Imaging and Clinical MRI, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Ansin 224, Boston, MA 02115. Address correspondence to K. J. Mortelé ([email protected]). The Radiology M and M Meeting: Misinterpretations, Misses, and Mimics 1 Mortelé countered consists of a bifid configura- outpouchings of the parenchyma more Focal dilation of the terminal portion tion with patent ducts of Wirsung (ven- than 1.0 cm beyond the anterior superior of the dorsal duct, also called “Santorin- tral) and Santorini (dorsal) present (Fig. pancreaticoduodenal artery [7]. These icele, is suggestive of relative obstruc- 1). Less common configurations include lobulations are present in approximately tion at the minor papilla [8]. MRCP, es- a rudimentary duct of Santorini and a 30% of people and are classified in three pecially when enhanced by IV secretin, dominant duct of Santorini [2]. main types: type I (anterior), 10%; type has been shown to be highly accurate for II (posterior), 19%; and type III (later- depicting pancreas divisum [9]. The Pancreatobiliary Union al), 5% [2, 3]. Another well-recognized The duct of Wirsung joins with the pseudomass is a prominence of the ante- Annular Pancreas common bile duct (CBD) and drains into rior and superior surface of the pancreat- Annular pancreas is a rare (1/2000) the duodenum through the major papilla ic body that abuts the posterior surface of congenital migratory anomaly due to [2, 3]. Before entering the duodenum, the the lesser omentum; this entity is known incomplete rotation of the ventral an- distal CBD and duct of Wirsung are en- as “tuber omentale” or “omental tuber- lage around the duodenum that leads to circled by the sphincter of Oddi, which osity” and should be not misinterpreted a segment of the pancreas encircling the typically measures 10–15 mm in length as a pancreatic neoplasm or lymph node second part of the duodenum [10]. There [2]. Sometimes, vivid contraction of the (Fig. 2) [2, 3]. are two types of annular pancreas: extra- sphincter of Oddi may simulate a stone mural and intramural. In the extramural in the distal CBD on MRCP; this has Ductal Fusion Anomalies type, the ventral pancreatic duct runs been referred to as the “pseudocalculus Discrepancy of the caliber of the MPD around the duodenum to join the main sign.” In most cases, the distal CBD and at the site of fusion of the dorsal and ven- pancreatic duct. In the intramural type, duct of Wirsung unite within the sphinc- tral ducts is a normal variant that may be the pancreatic tissue is intermingled ter of Oddi, forming a short (5 mm) com- confused for a site of stricturing [2]. The with muscle fibers in the duodenal wall mon channel with a distal dilation called absence of dilatation of the proximal or and small ducts drain directly into the the ampulla [2]. The duct of Santorini upstream ductal system enables differ- duodenum [2]. Annular pancreas can be drains the anterior and superior portions entiation between those entities (Fig. 3). diagnosed on the basis of CT and MRI of the head via the minor papilla. Duplication of the pancreatic ductal sys- findings that reveal pancreatic tissue and tem is fairly common, especially in the an annular duct encircling the descend- Classic Variants (Mimics) to Know tail, whereas parenchymal duplication is ing duodenum [11]. Pancreatic Fetal Lobulations extremely rare. Pancreatic shape alterations can simu- Pancreas divisum is reported in ap- Pancreatic Hypoplasia late pancreatic neoplasms. Pancreatic proximately 9% of the population [7] Hypoplasia (partial agenesis) results head and neck lobulations are defined as and results from nonfusion of the ven- from the absence of the ventral or, more tral and dorsal pancreatic ducts during commonly, the dorsal anlage. Hypoplasia embryologic life [8]. The ventral duct of the dorsal anlage, also known as “short (duct of Wirsung) drains only the ventral or truncated pancreas,” can be partial or anlage, whereas most of the gland (dor- complete and may be seen as a solitary sal anlage) drains via the minor papilla finding or in association with heterotax- through the dorsal duct or duct of Santo- ia syndromes [12]. Patients with dorsal rini [8] (Fig. 4). pancreatic agenesis often present with Fig. 1—Oblique coronal thick-slab MRCP image obtained in asymptomatic 39-year-old A B man shows normal bifid ductal configuration Fig. 2—43-year-old woman with ampullary adenocarcinoma. with duct of Wirsung (long arrow) and duct of A and B, Axial (A) and coronal (B) contrast-enhanced CT images show outpouching of pancreatic Santorini (short arrow). body in lesser sac (arrow). This omental tuberosity should not be confused with lymph node. 2 The Radiology M and M Meeting: Misinterpretations, Misses, and Mimics Imaging Pancreatic Disease ter of Oddi with formation of a long common channel (usually > 15 mm) [14]. This long common channel allows reflux of pancreatic secretions into the biliary system, possibly resulting in choledochal web and cyst formation. Conversely, reflux of bile into the pancreatic duct can cause acute recurrent pancreatitis. Top Five Miscalls to Avoid

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