Multimodality Imaging of Pancreatic and Biliary Congenital Anomalies 1

Transcription

1 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at EDUCATION EXHIBIT 715 Multimodality Imaging of Pancreatic and Biliary Congenital Anomalies 1 TEACHING POINTS See last page Koenraad J. Mortelé, MD Tatiana C. Rocha, MD Jonathan L. Streeter, MD Andrew J. Taylor, MD A wide spectrum of anomalies of the pancreas, the pancreatic ductal system, and the biliary tree are commonly encountered at radiologic evaluation. These anomalies may simulate various neoplastic, inflammatory, and posttraumatic conditions and should be part of the differential diagnosis for a variety of abnormalities found at diagnostic imaging. Anatomic variants, developmental anomalies (eg, pancreas divisum, annular pancreas, ectopic pancreas, pancreatic agenesis and hypoplasia), and congenital diseases (congenital pancreatic cysts, von Hippel Lindau disease, choledochal cysts), in addition to potential imaging pitfalls (uneven distribution of fat, pseudomasses ), can all pose a diagnostic challenge for the radiologist. Familiarity with these anomalies, the imaging techniques available for their study, and their variable imaging manifestations is necessary for differentiating them from other biliary and pancreatic conditions. A basic understanding of the embryologic development and normal anatomy of the pancreas and biliary tree is also essential for identifying these anomalies. RSNA, 2006 Abbreviations: CBD common bile duct, CHD common hepatic duct, EBD extrahepatic bile duct, ERCP endoscopic retrograde cholangiopancreatography, IBD intrahepatic bile duct, LHD left hepatic duct, MPD main pancreatic duct, RAD right anterior duct, RHD right hepatic duct, RPD right posterior duct 2006; 26: Published online /rg Content Code: 1 From the Department of Radiology, Division of Abdominal Imaging and Intervention (K.J.M., J.L.S.), and the Department of Radiology, 3D and Image Processing Center (T.C.R.), Brigham and Women s Hospital, Harvard Medical School, 75 Francis St, Boston, MA 02115; and the Department of Radiology, Clinical Science Center, University of Wisconsin, Madison, Wis (A.J.T.). Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received August 18, 2005; revision requested October 5 and received January 11, 2006; accepted January 11. All authors have no financial relationships to disclose. Address correspondence to K.J.M. ( kmortele@partners.org). RSNA, 2006

2 716 May-June 2006 RG f Volume 26 Number 3 Figure 1. Drawings illustrate the normal embryologic development of the pancreas and biliary tree. The ventral pancreatic bud (arrow in a and b) and biliary system arise from the hepatic diverticulum, and the dorsal pancreatic bud (arrowhead in a and b) arises from the dorsal mesogastrium. After clockwise rotation of the ventral bud around the caudal part of the foregut, there is fusion of the dorsal pancreas (located anterior) and ventral pancreas (located posterior). Finally, the ventral and dorsal pancreatic ducts fuse, and the pancreas is predominantly drained through the ventral duct, which joins the common bile duct (CBD) at the level of the major papilla. The dorsal duct empties at the level of the minor papilla. Introduction Congenital pancreatic and biliary anomalies are abnormalities not infrequently encountered at radiologic examination. Radiologists need to be familiar with these entities, the methods available for their study, and their variable imaging manifestations. Knowledge of the embryologic development and normal anatomy of the pancreas and biliary tree will help in understanding and identifying this group of disorders. In this article, we review the embryologic development and normal anatomy of the pancreas and biliary system and describe anatomic variants of these structures. In addition, we discuss and illustrate the key imaging features of a variety of developmental anomalies of the pancreas (pancreas divisum, annular pancreas, ectopic pancreas, pancreatic agenesis and hypoplasia) as well as congenital diseases of the pancreas (congenital pancreatic cysts, von Hippel Lindau disease) and biliary system (choledochal cysts). We also address potential pitfalls in the imaging of these anatomic structures, including uneven fat distribution and pseudomasses. Embryologic Development By the 4th week of embryologic growth, ventral (caudal) and dorsal (cranial) outpouchings develop at the junction of the foregut and midgut. The gallbladder, extrahepatic bile ducts (EBDs), central intrahepatic bile ducts (IBDs), and ventral pancreas with its ductal network are derived from the ventral outpouching, the hepatic diverticulum (Fig 1). The dorsal bud arises from the dorsal mesogastrium and is the precursor of the dorsal pancreas and its ductal system. At about this time, the developing ventral pancreas, gallbladder, and

3 RG f Volume 26 Number 3 Mortelé et al 717 Figure 2. Normal pancreatic anatomy. (a) Axial reformatted computed tomographic (CT) image shows the typical size, location, and lobulated appearance of the normal pancreas. (b) CT scan shows the normal triangular appearance of the uncinate process (arrow), with a straight posteromedial border and a gently concave anteromedial border (arrowhead). (c) Drawing illustrates the various parts (head, neck, body, and tail) of the pancreas. bile duct rotate clockwise (when viewed from the top) posterior to the duodenum and join the dorsal pancreas in the retroperitoneum. The ventral pancreatic duct and the CBD are, therefore, linked by their embryologic origins, resulting in the adult configuration of their common entrance into the duodenum at the major duodenal papilla (1). At approximately the 7th gestational week, the dorsal and ventral pancreatic ducts fuse in the region of the neck. The territory drained by each system can vary, but in general the dorsal pancreatic ductal system drains the tail, body, and anterior portion of the pancreatic head, whereas the ventral component drains the posterior aspect of the pancreatic head. Both dorsal and ventral ducts variably drain the uncinate process of the pancreatic head. The portion of the ventral duct between the dorsal-ventral fusion point and the major papilla is termed the duct of Wirsung. The portion of the dorsal duct proximal to the dorsal-ventral fusion point is called the main pancreatic duct (MPD); if a segment of the dorsal duct persists distal to the dorsal-ventral fusion point, it is termed the duct of Santorini, or accessory duct. In 30% of individuals, however, the duct of Santorini loses its communication with the minor duodenal papilla and persists only as a branch of the MPD (1). As mentioned earlier, the hepatic diverticulum gives off other structures in addition to the extrahepatic biliary tree and ventral pancreas. The gallbladder arises from the extrahepatic ductal system, with the hepatic parenchyma and intrahepatic ducts being derived from the endoderm at the tip of the diverticulum. The IBDs develop as part of a complex process. At first, there is a web of interconnecting channels within the liver substance. These channels are then obliterated, after which recanalization occurs to form the mature intrahepatic ducts. If interconnecting ducts persist, accessory, anomalous, or aberrant bile ducts may result (1,2). Normal Anatomy Pancreas The pancreas is a coarsely lobulated gland typically cm in length and located in the anterior pararenal space of the retroperitoneum. The gland can be divided into four parts: head, neck, body, and tail. The pancreatic head is located within the curve of the duodenum, to the right of the superior mesenteric vein. The uncinate process is a prolongation of the caudal part of the head, which is oriented toward the left. It has a triangular appearance, and its anteromedial border can be straight or concave. The pancreatic neck is the constricted portion to the left of the head and ventral to the superior mesenteric vein. The pancreatic body and tail are located behind the lesser sac and the stomach. The border between the body and tail is not clearly defined but can be determined using one-half of the distance between the neck and the end of the pancreas (Fig 2) (3).

4 718 May-June 2006 RG f Volume 26 Number 3 Figure 3. Normal pancreatic ductal anatomy. (a) Drawing illustrates the MPD, the duct of Wirsung, and the duct of Santorini. The latter empties at the minor papilla. (b) Coronal magnetic resonance (MR) cholangiopancreatogram shows the normal bifid configuration of the pancreas with main drainage of the gland through the duct of Wirsung (arrow). The duct of Santorini (arrowhead) drains into the minor papilla. (c) Coronal MR cholangiopancreatogram shows a narrowed intersphincteric segment of the CBD (arrow) and pancreatic duct due to contraction of the sphincter of Oddi. (d) Drawing illustrates the sphincter of Oddi complex (arrow) encompassing the distal CBD and pancreatic duct. The diameter of the MPD is normally 3.5 mm in the head, 2.5 mm in the body, and 1.5 mm in the tail, and the length of the MPD varies from 9.5 to 25 cm. There are approximately 27 possible ductal configurations. Typically, the MPD has side branches that enter the duct at right angles. The duct of Wirsung unites with the CBD and drains into the major papilla. The duct of Santorini, or accessory duct, drains the anterior and superior portion of the head into the minor papilla. The distal CBD and duct of Wirsung traverse the sphincter of Oddi (which consists of three separate smooth muscles) to enter the duodenum (Fig 3). In most cases (80% 90%), the CBD and duct of Wirsung unite within this sphincteric segment, with the muscular wrap being mm in length. This common channel may be long (Y-type configuration) or short (V type). A high junction (above the sphincter) may theoretically allow reflux of pancreatic secretions into the bile duct. Such reflux is one of the proposed causes for the development of some types of choledochal cysts (4). There are three possible anatomic relationships between the CBD and the pancreatic head: The CBD is partially covered posteriorly by pancreatic tissue in 51.5% of the population, totally covered in 30%, and not covered at all in 16.5% (Fig 4). Occasionally, the CBD courses lateral to the pancreatic head (5).

5 RG f Volume 26 Number 3 Mortelé et al 719 Figure 4. CT scans show the three possible anatomic relationships between the CBD (arrow) and the pancreas: partial coverage of the CBD by pancreatic tissue (a), total coverage (b), and no coverage (c). Biliary System The intrahepatic biliary system runs parallel to the portal venous supply of the liver. The right hepatic duct (RHD) drains the segments of the right hepatic lobe (V VIII) and has two major branches: the right posterior duct (RPD), which drains the posterior segments (VI and VII), and the right anterior duct (RAD), which drains the anterior segments (V and VIII). The RPD has an almost horizontal course, whereas the RAD tends to have a more vertical orientation. The RPD usually runs posterior to the RAD and, with a medial (ie, left-sided) approach, fuses with the RAD to form the RHD (Fig 5). The LHD is formed by segmental tributaries draining segments II IV. The CHD is formed by the fusion of the typically short RHD and the longer LHD. The bile duct draining the caudate lobe usually joins the origin of the LHD or RHD (6). The cystic duct classically joins the CHD below the confluence of the RHD and LHD with a lateral approach to the CHD. This normal biliary anatomy is thought to be present in 58% of individuals (7). Figure 5. Normal biliary anatomy. Coronal MR cholangiopancreatogram shows the left hepatic duct (LHD) and RHD (long arrow) forming the common hepatic duct (CHD). Note that the RHD is formed by two branches: the RPD (short arrow), which drains posterior segments VI and VII; and the RAD (arrowhead), which drains anterior segments V and VIII.

6 720 May-June 2006 RG f Volume 26 Number 3 Figure 6. Variant pancreatic ductal anatomy. Coronal MR cholangiopancreatograms show a dominant dorsal duct with a santorinicele (arrow in a) and ansa pancreatica (arrow in b). Anatomic Variants Pancreas There is a gradual decrease in the size of the pancreas with age. Its anteroposterior dimensions in persons years of age are as follows: 24 mm ( 3.6 mm) for the head, 16 mm ( 2.0 mm) for the body, and 15.1 mm ( 1.9 mm) for the tail (8). The downstream ductal configuration most commonly manifests as a bifid configuration formed by the ducts of Wirsung and Santorini (60% of cases). Less common configurations include a rudimentary duct of Santorini (30% of cases), a dominant duct of Santorini (1%), and ansa pancreatica, in which the duct of Santorini forms a sigmoid curve as it courses to the duct of Wirsung (Fig 6) (9). Narrowing of the caliber of the duct at the knee of the MPD can be seen, a finding that represents the site of fusion of the dorsal and ventral ducts. The absence of dilatation of the proximal, or upstream, ductal system allows differentiation of this normal variant from a true stricture (Fig 7). Duplication anomalies of the MPD are fairly common, whereas those involving the parenchyma from the dorsal and ventral anlagen are extremely rare (Fig 8). Figure 7. Variant pancreatic ductal anatomy. MR cholangiopancreatogram shows a change in the caliber of the pancreatic duct (arrow) at the level of fusion between the MPD and the duct of Wirsung. Note the lack of upstream dilatation, which indicates that this change in caliber represents an anatomic variant. Figure 8. Variant pancreatic ductal anatomy. Coronal endoscopic retrograde cholangiopancreatographic (ERCP) image shows duplicate pancreatic ducts (arrows) in the tail of the pancreas.

7 RG f Volume 26 Number 3 Mortelé et al 721 Figure 9. Variant biliary ductal anatomy. Coronal MR cholangiopancreatograms show the RPD (arrow in a) draining into the LHD and a medial and low insertion of the cystic duct (arrow in b). Teaching Point Biliary System The RPD is by far the most anomalous in terms of insertion site. Drainage of the RPD into the LHD before its confluence with the RAD is the most common anatomic variant of the biliary system and has been reported to occur in 13% 19% of the population (Fig 9) (6,7,10). In approximately 12% of the population, the RPD will not pass the RAD posteriorly, but will empty into the right aspect of the RAD (10). The so-called triple confluence is another common variant of the main hepatic biliary branches (11% of the population). This anomaly is characterized by simultaneous emptying of the RPD, RAD, and LHD into the CHD to form a trifurcation. These variants at the level of the confluence become important in patients being considered as potential donors for right hepatic lobe transplantation. There are three common variants in the cystic ductal anatomy: a low cystic duct insertion, characterized by fusion of the cystic duct with the distal third of the EBD (9% of cases) (Fig 9); a medial cystic duct insertion, in which the cystic duct drains into the left side of the CHD (10% 17%); and a parallel course of the cystic duct with the CHD (1.5% 25%), which is thought to be present when the cystic duct closely adheres to the CHD and courses parallel to it for at least 2 cm. Familiarity with these variants is important prior to laparoscopic cholecystectomy due to the risk of injury to the cystic and hepatic ducts posed by this procedure. Several less common and usually more complicated anatomic variations of the biliary ducts can also be seen (11). The direct drainage of the RPD into the CHD, from either the right or left side, is a variant also known as an aberrant hepatic duct and has been reported to occur in 5% (from the right) and less than 1% (from the left) of individuals. Accessory hepatic ducts are observed in approximately 2% of individuals and may originate from and course along either the left or right ductal system. Pancreas and Biliary System An anomalous pancreaticobiliary junction is characterized by fusion of the pancreatic duct and CBD outside the duodenal wall, with formation of a long common channel (usually 15 mm) (12,13). As mentioned earlier, the presence of a long common channel may allow reflux of pancreatic secretions into the biliary system, possibly resulting in choledochal web or cyst formation Teaching Point

8 722 May-June 2006 RG f Volume 26 Number 3 Figure 10. Abnormal common channel. (a) Drawing illustrates a long common channel ( 15 mm). Note that the sphincter of Oddi does not reach the confluence (arrow) of the ducts. (b) ERCP image obtained in a child shows a long common channel (arrowhead) and the presence of a CBD web (arrow). (Fig 10). Conversely, reflux of bile into the pancreatic duct can cause pancreatitis. An anomalous junction should be diagnosed and surgically treated before pancreaticobiliary complications (including cholangiocarcinoma) develop (13). Developmental Anomalies of the Pancreas Pancreas Divisum Pancreas divisum is the most common congenital anomaly of the pancreatic ductal system, being reported in 4% 10% of the population (14). This anomaly results when the ventral and dorsal pancreatic ducts fail to fuse. The ventral duct (duct of Wirsung) drains only the ventral pancreatic anlage, whereas the majority of the gland empties into the minor papilla through the dorsal duct (duct of Santorini) (2). Focal dilatation of the terminal portion of the dorsal pancreatic duct, a condition known as santorinicele, is described in association with pancreas divisum and relative obstruction at the minor papilla (15 17). Pancreas divisum is usually asymptomatic (15) but is more frequently seen in patients with chronic abdominal pain and idiopathic pancreatitis than in the general population (18 20). The definitive diagnosis of pancreas divisum is made with endoscopic retrograde pancreatography (21,22). Multi detector row CT may also depict pancreas divisum, but only when the pancreatic duct is visualized (23). MR pancreatography has been shown to be highly sensitive and specific for pancreas divisum (Fig 11) (24,25). MR cholangiopancreatography with secretin stimulation helps in identifying pancreas divisum and santorinicele (17). Endoscopic retrograde pancreatography shows only ventral duct opacification when standard cannulation of the major papilla is performed. MR pancreatography, on the other hand, demonstrates noncommunicating dorsal and ventral ducts, independent drainage sites, and a dominant dorsal pancreatic duct (25). The ventral duct is typically short and very narrow. Its branching pattern may be treelike, or the duct may be normal appearing but markedly diminished in size. At times, the ventral duct may be highly atretic. The dorsal duct is typically larger in caliber (23). Annular Pancreas Annular pancreas is a rare congenital anomaly in which incomplete rotation of the ventral anlage leads to a segment of the pancreas encircling the second part of the duodenum (26). There are two major hypotheses concerning the development of annular pancreas: adhesion of the right ventral anlage to the duodenal wall (Lecco s theory), and persistence of the left ventral anlage (Baldwin s theory). Each theory has some inherent inconsistencies and can account for only a few types of annular pancreas. A third theory has been presented and suggests that the tip of the left ventral anlage adheres to the duodenum, with the duodenal rotation resulting in a ring of pancreatic tissue. In this theory, several arrange-

9 RG f Volume 26 Number 3 Mortelé et al 723 Figure 11. Pancreas divisum. (a) Coronal MR cholangiopancreatogram shows drainage of the pancreas through the duct of Santorini (arrow). Note that the MPD is not fused with the duct of Wirsung (arrowhead). (b) CT scan obtained in a patient with acute recurrent pancreatitis and pancreas divisum shows a dilated duct of Santorini (arrowhead). Figure 12. Annular pancreas. (a) Axial T2-weighted MR image shows the pancreas (arrow) encircling the descending portion of the duodenum. (b) Coronal MR cholangiopancreatogram shows the duct of Wirsung (arrowhead) encircling the duodenum. ments of annular pancreas are possible, depending on whether the tip of the left ventral anlage is proximal or distal to the bile ducts (27). Annular pancreas has a prevalence of one in 2,000 persons and occurs either as an isolated finding or with other congenital abnormalities (28,29). In approximately one-half of symptomatic cases, annular pancreas will manifest in the neonate with gastrointestinal obstruction or bile duct obstruction, possibly associated with pancreatitis. In adults, it may manifest with symptoms of peptic ulcer disease, duodenal obstruction, or pancreatitis (2,30). In general, annular pancreas obstructs the duodenum in 10% of cases. There are two types of annular pancreas: the extramural type and the intramural type. In the extramural type, the ventral pancreatic duct encircles the duodenum to join the MPD. In the intramural type, the pancreatic tissue is intermingled with muscle fibers in the duodenal wall, and small ducts drain directly into the duodenum (26). Annular pancreas can be diagnosed on the basis of CT and MR imaging findings that reveal pancreatic tissue and an annular duct encircling the descending duodenum (Fig 12) (31).

10 724 May-June 2006 RG f Volume 26 Number 3 Ectopic Pancreas Ectopic pancreas occurs in 0.6% 13.7% of the population (32). This ectopic tissue can be found in the stomach (26% 38% of cases), duodenum (28% 36%), jejunum (16%), Meckel diverticulum, or ileum. Rarely, it occurs in the colon, esophagus, gallbladder, bile ducts, liver, spleen, umbilicus, mesentery (Fig 13), mesocolon, or omentum (28,33 35). The ectopic tissue usually measures cm in its largest dimension (rarely up to 5 cm) and is located in the submucosa in approximately 50% of cases. Ectopic pancreas in the gastrointestinal tract is usually asymptomatic, although complications such as stenosis, ulceration, bleeding, and intussusception may develop (28,34). Rarely, pancreatic heterotopia can be the result of (a) tumors developing from one of the cellular elements, including adenocarcinoma and endocrine tumors; or (b) inflammation characterized by the presence of fat stranding around the ectopic pancreas (32). Pancreatic Agenesis and Hypoplasia Total agenesis of the pancreas is extremely rare and is incompatible with life (2,36). It is associated with other malformations such as gallbladder aplasia, polysplenia, and fetal growth retardation. The mutation of a developmental protein, IPF1, is responsible for the absence of the gland. Hypoplasia (partial agenesis) (Fig 14) results from the absence of the ventral or dorsal anlage. Absence of the dorsal anlage is visualized as a short or truncated pancreas and can be partial or complete. It may be seen as a solitary finding or in association with heterotaxia syndromes (28). Partial agenesis of the dorsal pancreas is relatively more common than agenesis of the ventral portion, but complete agenesis of the dorsal pancreas is extremely rare (36). Patients with agenesis of the dorsal pancreas often present with nonspecific abdominal pain, which may or may not be caused by pancreatitis. Many patients also have diabetes mellitus. When agenesis of the dorsal pancreas is suspected, it is critical to rule out pancreatic carcinoma with upstream atrophy of the gland (36). Isolated hypoplasia of the uncinate process has also been reported (37). At imaging, dorsal pancreatic hypoplasia manifests as a short, rounded pancreatic head adjacent to the duodenum with absence of the pancreatic Figure 13. Ectopic pancreas. CT scan obtained in a patient with abdominal pain shows ectopic pancreatic tissue (arrow) within the small bowel mesentery. Surgery helped confirm the presence of an inflamed ectopic pancreas. neck, body, and tail. In patients with complete agenesis of the dorsal pancreas, the neck, body, and tail of the pancreas, the duct of Santorini, and the minor duodenal papilla are all absent. In cases of partial agenesis of the dorsal pancreas, the size of the body of the pancreas varies, there is a remnant of the duct of Santorini, and the minor duodenal papilla is present (36). Pancreas Congenital Diseases Congenital Pancreatic Cysts. Congenital pancreatic cysts are exceedingly rare. They have a female predilection and typically manifest as an asymptomatic palpable mass. Patients may also present with epigastric pain, jaundice, and vomiting related to the compression of surrounding structures. These cysts can be single or multiple and are most commonly located in the tail and body of the pancreas (28). Multiple congenital cysts are associated with other anomalies, such as von Hippel Lindau disease (Fig 15) and hepatorenal polycystic disease (38). Von Hippel Lindau Disease. Von Hippel Lindau disease is an autosomal dominant disorder with variable penetrance that is characterized by retinal angiomas and central nervous system hemangioblastomas (39). Pancreatic cysts are relatively common in von Hippel Lindau disease, and involvement can range from a single cyst to

11 RG f Volume 26 Number 3 Mortelé et al 725 Figure 14. Pancreatic hypoplasia. (a) CT scan shows the pancreatic head (arrow) and absence of the pancreatic neck, body, and tail. (b) CT scan obtained in a patient with heterotaxia syndrome shows a truncated midline pancreas (arrow). Figure 15. Von Hippel Lindau disease. (a) Contrast material enhanced CT scan shows enhancing septa separating congenital pancreatic cysts. (b) Axial T2-weighted MR image shows cystic replacement of the pancreas and a serous microcystic pancreatic adenoma (arrow). cystic replacement of the gland (Fig 15b). Peripheral calcifications may also be present. Pancreatic lesions may be the only manifestation of the disease for many years (28,38). Other pancreatic neoplasms not infrequently seen in von Hippel Lindau disease include microcystic serous pancreatic adenoma (Fig 15b) and endocrine tumors. Biliary System Choledochal cysts are rare congenital biliary tract anomalies characterized by biliary tree dilatation. The five subtypes as defined by Todani probably have different pathophysiologic features but are grouped together according to the cystic changes they have in common. Two principal (but not necessarily mutually exclusive) theories exist regarding the cause of the most common types of choledochal cysts. The first theory relates to the presence of a long common channel, whereas the second suggests distal ductal obstruction as a factor (40). Most choledochal cysts are diagnosed in childhood; however, up to 20% of cysts manifest in adults. The cysts have a 4:1 female predilection. Their manifestation in adults is nonspecific, which often leads to a delay in diagnosis (40). The triad of abdominal pain, a right upper quadrant mass, and jaundice is more prevalent in the pediatric population and is reported to occur in 2% 38% of patients (41). As mentioned earlier, choledochal cysts include the disorders characterized by dilatation of all or part of the EBDs or IBDs (Figs 16, 17) (42).

12 726 May-June 2006 RG f Volume 26 Number 3 Figure 16. Choledochal cysts. (a, b) Drawing (a) and coronal MR cholangiopancreatogram (b) show a type I choledochal cyst (arrow in b). (c, d) Drawing (c) and ERCP image (d) show a diverticulum (arrow in d) of the EBD, a finding that represents a type II choledochal cyst. (e, f ) Drawing (e) and ERCP image (f ) show a choledochocele, or type III choledochal cyst (arrow in f ).

13 RG f Volume 26 Number 3 Mortelé et al 727 Figure 17. (a, b) Drawing (a) and coronal MR cholangiopancreatogram (b) show type IV choledochal cysts. (c, d) Drawing (c) and ERCP image (d) show a type V choledochal cyst (Caroli disease). (e) Caroli disease. Contrast-enhanced T1-weighted MR image shows saccular dilatation of the IBD and the central dot sign (arrow).

14 728 May-June 2006 RG f Volume 26 Number 3 Todani Type I Choledochal Cyst. Todani type I choledochal cysts (Fig 16a, 16b) are confined to the EBD. They can be further subdivided into type Ia (diffuse) cysts, which involve the entire EBD; type Ib (focal) cysts, which involve only a focal segment of the EBD; and type Ic (fusiform) cysts, which involve only the CBD. Type I cysts result from an anomalous pancreaticobiliary union characterized by formation of a long, frequently ectatic common channel. Todani Type II Choledochal Cyst. Todani type II choledochal cysts (Fig 16c, 16d) represent true diverticula of the EBD. Todani Type III Choledochal Cyst. Todani type III choledochal cysts, or choledochoceles, represent ectasia of an intramural CBD segment. These lesions are not embryologically related to the cystic dilatations of the other choledochal cysts. Type III cysts typically manifest as focal dilatation of the intraduodenal segment of the distal CBD. Patients can present with intermittent biliary colic, jaundice, and pancreatitis. attacks of right upper quadrant pain, fever, and, more rarely, jaundice (6). Imaging studies show intrahepatic saccular or fusiform dilated cystic structures of varying sizes that communicate with the biliary tree. The presence of a tiny dot with contrast enhancement within the dilated IBD (central dot sign) is considered highly suggestive of Caroli disease (45). The central dot sign is produced by enhancing portal branches surrounded by cystic alterations of the IBDs (26). Intraluminal biliary calculi may be demonstrated as well. The differential diagnosis includes primary sclerosing cholangitis, recurrent pyogenic cholangitis, autosomal dominant polycystic liver disease, biliary hamartomas, microabscess, biliary papillomatosis, and, occasionally, obstructive biliary dilatation (43). Associated conditions include choledochal cysts, cholangiocarcinoma, and renal cystic disease such as medullary sponge kidney and tubular ectasia (46). Potential Pitfalls Teaching Point Todani Type IV Choledochal Cyst. Todani type IV choledochal cysts (Fig 17a, 17b) are by definition multiple and can have both intrahepatic and extrahepatic components. They can be further subdivided into type IVa cysts, which involve both the EBD and the IBD; and type IVb cysts, which involve only the EBD with multiple saccular dilatations. Todani Type V Choledochal Cyst (Caroli Disease). Todani type V choledochal cyst, or Caroli disease (Fig 17c 17e), is a rare congenital cystic dilatation of the IBDs. It is an autosomal recessive disorder that results from the arrest of or a derangement in the normal embryologic remodeling of ducts, which in turn causes varying degrees of destructive inflammation and segmental dilatation. If the large IBDs are affected, the result is Caroli disease, whereas abnormal development of the small interlobular bile ducts results in congenital hepatic fibrosis. If all levels of the intrahepatic biliary tree are involved, features of both congenital hepatic fibrosis and Caroli disease are present; this condition has been termed Caroli syndrome (43,44). The clinical features reflect recurrent bouts of cholangitis due to bile stasis, including recurrent Uneven Distribution of Fat Extreme pancreatic lipomatosis can be seen in cystic fibrosis and Shwachman-Diamond syndrome, as well as in diabetic, obese, and elderly patients. When the condition is severe, the pancreas will have the same signal intensity and density as the mesenteric fat and thus may not be identifiable. Differentiation between lipomatosis and pancreatic agenesis is important and is made on the basis of whether the ductal system is present (lipomatosis) or absent (agenesis). Sometimes, fatty replacement is not homogeneous throughout the pancreas, since the ventral and dorsal portions of the gland demonstrate different histologic compositions. Focal sparing of the peribiliary region with fatty replacement of the anterior portion of the pancreatic head is a common finding on imaging studies. There are four different types of uneven pancreatic lipomatosis. Type 1a (35% of cases) is characterized by replacement of the head with sparing of the uncinate process and peribiliary region; type 1b (36%), by replacement of the head, neck, and body, with sparing of the uncinate process and peribiliary region; type 2a (12%), by replacement of the head, including the uncinate process, and sparing of the peribiliary region; and type 2b (18%), by total replacement of the pancreas with sparing of the peribiliary region (Fig 18) (47). Teaching Point

15 RG f Volume 26 Number 3 Mortelé et al 729 Figure 18. Uneven fatty replacement of the pancreas. (a) Drawings illustrate the four different patterns of fatty replacement of the pancreas (gray areas). The percentage of cases of uneven pancreatic lipomatosis represented by each type is also indicated. (b) CT scan shows type 1a fatty replacement of the pancreatic head (arrow). Pseudomasses Alterations in the shape of the pancreas manifesting as pseudomasses can simulate pancreatic neoplasms. Pancreatic head and neck lobulations are defined as outpouchings of the gland more than 1 cm beyond the anterior superior pancreaticoduodenal artery. These variations are seen in approximately 34% of individuals upon close examination. There are three main types: type I (anterior), seen in 10% of individuals; type II (posterior), seen in 19%; and type III (horizontal), seen in 5% (Fig 19) (48). Another well-recognized pseudomass is a prominence on the anterior surface of the pancreatic body to the left of the superior mesenteric vessels that abuts the posterior surface of the lesser omentum. This entity is known as tuber omentale and should be not misinterpreted as a true pancreatic neoplasm. Teaching Point Figure 19. Pancreatic head configurations. (a) Drawings illustrate the normal appearance of the pancreatic head and the three variant (pseudomass) appearances. (b) CT scan shows a posterior configuration (arrow). Conclusions Congenital pancreatic and biliary anomalies are commonly encountered at radiology. Radiologists should be familiar with these anomalies, the imaging techniques available for their study, and their variable imaging manifestations to differentiate them from other biliary and pancreatic conditions. A basic understanding of the embryologic development and normal anatomy of the pancreas and biliary tree is mandatory for identifying this group of disorders.

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18 RG Volume 26 Volume 3 May-June 2006 Mortelé et al Multimodality Imaging of Pancreatic and Biliary Congenital Anomalies Koenraad J. Mortelé, MD et al 2006; 26: Published online /rg Content Code: Page 721 Drainage of the RPD into the LHD before its confluence with the RAD is the most common anatomic variant of the biliary system and has been reported to occur in 13% 19% of the population (Fig 9) (6,7,10). Page 721 An anomalous pancreaticobiliary junction is characterized by fusion of the pancreatic duct and CBD outside the duodenal wall, with formation of a long common channel (usually >15 mm) (12,13). Page 728 If the large IBDs are affected, the result is Caroli disease, whereas abnormal development of the small interlobular bile ducts results in congenital hepatic fibrosis. If all levels of the intrahepatic biliary tree are involved, features of both congenital hepatic fibrosis and Caroli disease are present; this condition has been termed Caroli syndrome (43,44). Page 728 Extreme pancreatic lipomatosis can be seen in cystic fibrosis and Shwachman-Diamond syndrome, as well as in diabetic, obese, and elderly patients. Page 729 Another well-recognized pseudomass is a prominence on the anterior surface of the pancreatic body to the left of the superior mesenteric vessels that abuts the posterior surface of the lesser omentum.