DOI:10.2214/AJR.05.0774
AJR 2006; 187:1544-1553
© American Roentgen Ray Society
Congenital Anomalies and Normal Variants of the Pancreaticobiliary Tract and the Pancreas in Adults: Part 2, Pancreatic Duct and Pancreas
Jinxing Yu1,
Mary Ann Turner1,
Ann S. Fulcher1 and
Robert A. Halvorsen1
1 All authors: Department of Radiology, VCU Health Systems, Virginia
Commonwealth University, 1250 E Marshall St., Richmond, VA 23298-0615.
Received May 5, 2005;
accepted after revision August 31, 2005.
Address correspondence to J. Yu
(jiyu{at}hsc.vcu.edu).
Abstract
OBJECTIVE. The purpose of this article is to highlight the imaging
features of congenital anomalies and normal variants of the pancreatic duct
and the pancreas using contemporary imaging techniques such as MR
cholangiopancreatography (MRCP), MRI, and helical CT.
CONCLUSION. Congenital anomalies and normal variants of the
pancreatic duct and the pancreas may be clinically significant and may create
a diagnostic challenge. Recognition of the updated imaging features of these
entities is important in clinical management and for avoiding
misdiagnosis.
Keywords: congenital anomalies • CT • developmental anomalies • MRI • pancreas
Introduction
Congenital anomalies and normal variants of the pancreatic duct and the
pancreas may not be detected until adulthood and then are often detected as
incidental findings in asymptomatic patients
[1-8].
Because an increasing number of patients undergo MRI, MR
cholangiopancreatography (MRCP), and CT examinations, these anomalies are
recognized more frequently. At the same time, the rapid advances in and
emergence of surgical and endoscopic procedures, such as insertion of stents
in the minor papilla for pancreatic divisum
[2], make recognition of these
variants, particularly those of clinical significance, very important.
Congenital anomalies and normal variants of the pancreas and the pancreatic
duct include pancreas divisum, annular pancreas, ectopic pancreatic tissue,
variations of pancreatic contour, fatty replacement and fat sparing of the
pancreas, pancreatic cysts, and variations of pancreatic ducts. The MRI, MRCP,
CT, and direct cholangiographic features of these entities are presented along
with clues to help differentiate them from acquired diseases in adults.
Pancreas Divisum
Pancreatic ductal anatomy (Figs.
1A,
1B, and
1C) can be subject to a number
of variations. Pancreas divisum is the most common congenital pancreatic
ductal anatomic variant, occurring in approximately 4-14% of the population at
autopsy series, 3-8% at ERCP, and 9% at MRCP
[1-5].
The abnormality results from failure of the dorsal and ventral pancreatic
anlage to fuse during the sixth to eighth weeks of gestation. In most cases of
pancreatic divisum, no communication exists between the dorsal and ventral
pancreatic ducts. In some patients, the ventral pancreatic duct may be absent.
In all cases, most pancreatic secretions drain through the minor ampulla.
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Fig. 1C —Diagram of pancreatic ductal anatomic variants. Typical
pancreatic divisum with small ventral duct (arrows) drains via major
papilla. Larger dorsal duct (open arrows) drains via minor
papilla.
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For many years, ERCP has been the primary means of diagnosing pancreas
divisum. MRCP provides a noninvasive means of diagnosing pancreas divisum
without the use of contrast material and avoids the risk of ERCP-induced
pancreatitis. The main features of pancreas divisum when using MRCP include
the dorsal pancreatic duct in direct continuity with the duct of Santorini,
which drains into the minor ampulla, and a ventral duct, which does not
communicate with the dorsal duct but joins with the distal bile duct to enter
the major ampulla [3]
(Fig. 2). With the advent of
MDCT scanners, pancreas divisum may be seen using CT as well
[4]
(Fig. 3).
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Fig. 2 —48-year-old woman with liver disease. Coronal MR
cholangiopancreatography (MRCP) thick-slab image shows main pancreatic duct
(DP) entering minor papilla (arrowhead) in duodenum without joining
with common bile duct (CBD). Point of entry is cephalad to major papilla
(open arrow). Common bile duct (CBD) joins with ventral pancreatic
duct (VP) and both enter major papilla. There is no communication between
dorsal duct (DP) and ventral duct (VP). Gallbladder (GB) is noted.
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Fig. 3 —63-year-old woman with congestive heart failure and abdominal
pain. Axial CT image shows main pancreatic duct (DP) running anteriorly and
parallel to common bile duct (open arrow). Ventral duct (VP) joins
bile duct before entering duodenum (D). Pancreas (P) is noted.
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The clinical relevance of pancreas divisum remains controversial. Most
patients with pancreas divisum are asymptomatic
[2-5].
However, in some patients, this anomaly is associated with recurrent episodes
of pancreatitis. Of those with idiopathic recurrent pancreatitis (Figs.
4A and
4B), 12-26% of patients have
pancreas divisum, as opposed to 3-9% of the general population
[5]. It is postulated that in
pancreas divisum, the duct of Santorini and the minor ampulla are too small to
adequately drain the secretions produced by the pancreatic body and tail
[1-5].
Recent research shows that the administration of secretin improves the
sensitivity of MRCP in diagnosing pancreatic divisum.
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Fig. 4A —44-year-old woman with recurrent pancreatitis. Coronal MR
cholangiopancreatography (MRCP) thin-slab image shows dilated dorsal
pancreatic duct (DP) entering duodenum (D) without joining common bile duct
(CBD). Point of entry of dorsal pancreatic duct is cephalad and anterior to
major papilla. Pancreatic ductal side branch ectasia (open arrow) and
small pseudocysts (arrowheads) are noted, consistent with chronic
pancreatitis. Gallbladder (GB) is noted.
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Fig. 4B —44-year-old woman with recurrent pancreatitis. Coronal MRCP
thin-slab image posterior to A shows common bile duct (CBD) and dilated
ventral duct (VP) entering major papilla (arrow) in duodenum (D).
Dilated pancreatic duct in pancreatic tail (DP) is present. Gallbladder (GB)
is noted.
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Annular Pancreas
Annular pancreas is a rare anomaly (1/20,000 people) in which a band of
pancreatic tissue surrounds the descending duodenum, either completely or
incompletely, and is in continuity with the head of the pancreas
[1,
6] (Figs.
5A and
5B). The most widely accepted
theory of etiopathogenesis is that the ventral pancreatic anlage is
responsible for the anomaly by dividing early into two segments
[6]. The anomaly may be
discovered incidentally in asymptomatic patients
[6]. In others, annular
pancreas is associated with duodenal stenosis, postbulbar ulcerations,
pancreatitis, or biliary obstruction. Before the advent of CT, MRI, and MRCP,
the diagnosis of annular pancreas was usually established by ERCP, as an
aberrant pancreatic duct communicating with the main pancreatic duct and
encircling the duodenum. CT or MR images may show normal pancreatic tissue,
with or without a small pancreatic duct, encircling the duodenum
[6] (Figs.
6A,
6B,
6C,
7A, and
7B). The findings at upper
gastrointestinal examinations are often characteristic in that narrowing of
the second portion of the duodenum is shown
(Fig. 7C). Surgical resection
is recommended for symptomatic cases.
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Fig. 6A —23-year-old man with elevated pancreatic enzymes after
trauma. Axial CT image shows large pseudocyst (C) in pancreas (P) consistent
with pancreatic injury. Pancreatic tissue (arrows) completely
surrounds descending duodenum (D).
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Fig. 6B —23-year-old man with elevated pancreatic enzymes after
trauma. Coronal MR cholangiopancreatography (MRCP) thin-slab image shows
pancreatic duct (arrows) in pancreatic tissue adjacent to lateral
wall of descending duodenum (D). Common bile duct (CBD) is noted.
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Fig. 6C —23-year-old man with elevated pancreatic enzymes after
trauma. ERCP image shows pancreatic duct (P) making loop in its proximal
portion. Loop (arrows) of pancreatic duct encircles second portion of
duodenum (D). Common bile duct (CBD) is noted.
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Fig. 7A —51-year-old woman with leukemia. Axial CT image shows
pancreatic tissue (P) and pancreatic duct (arrows) encircling
descending duodenum (D). Common bile duct (CBD) and gallbladder (GB) are
noted.
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Fig. 7B —51-year-old woman with leukemia. Axial CT image superior to
A shows pancreatic tissue (P) and pancreatic duct (arrows)
extending lateral to descending duodenum (D). Gallbladder (GB) are noted.
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Fig. 7C —51-year-old woman with leukemia. Image from upper
gastrointestinal series shows extrinsic defect (solid arrows) with
focal narrowing (open arrows) of descending duodenum (D). Stomach (S)
and jejunum (J) are noted.
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Ectopic Pancreatic Tissue
Ectopic rests of pancreatic tissue are usually located in either the
submucosa of the gastric antrum or the proximal portion of the duodenum
[7]. In most instances, ectopic
pancreatic tissue represents an incidental finding, having an incidence of
1-10%. However, if the ectopic pancreatic tissue is functional, it is subject
to the same inflammatory and neoplastic disorders that involve the normal
pancreas. On upper gastrointestinal examination, an ectopic pancreas appears
as an extramucosal, smooth, broad-based lesion either along the greater
curvature of the gastric antrum or in the proximal duodenum. In 45% of the
cases of ectopic pancreas discovered on upper gastrointestinal examination,
the ectopic pancreatic tissue contains a central small collection of barium,
which is indicative of a central niche or umbilication. It is this finding
that is diagnostic of ectopic pancreatic tissue
(Fig. 8). Laparoscopic gastric
wedge resection is a safe and effective treatment for symptomatic pancreatic
rests located in the stomach
[7].
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Fig. 8 —23-year-old man with upper abdominal pain. Image from upper
gastrointestinal series shows extramucosal, smooth filling defect (solid
arrows) in gastric antrum (A). Central umbilication (open arrow)
is present within lesion. Endoscopy confirmed diagnosis of ectopic pancreas.
Duodenum (D) is noted.
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Fig. 9A —31-year-old man with abnormal results of liver function test.
Axial CT image shows soft-tissue attenuation focus (arrows) arising
from pancreas (P) that is similar in attenuation to tissue in pancreatic head
(P).
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Fig. 9B —31-year-old man with abnormal results of liver function test.
T1-weighted axial unenhanced fat-suppressed image shows that soft-tissue
protuberance (arrows) is isointense to pancreatic head (P). Enhanced
images (not shown) revealed that protuberance enhanced in fashion identical to
pancreatic head.
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Fig. 9C —31-year-old man with abnormal results of liver function test.
Coronal MR cholangiopancreatography (MRCP) image shows branch
(arrows) of pancreatic duct (P) in soft-tissue protuberance that
drains into main pancreatic duct. Common bile duct (CBD) and duodenum (D) are
noted. These findings are indicative of contour anomaly of pancreas.
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Fig. 11A —62-year-old woman with possible mass in pancreatic head seen
on chest CT. Axial CT scan shows focal fatty infiltration (arrows) in
pancreatic head. There is fat sparing in pancreatic neck (P). Duodenum (D) is
noted.
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Fig. 11C —62-year-old woman with possible mass in pancreatic head seen
on chest CT. Out-of-phase T1-weighted axial image shows significant signal
decrease in pancreatic head (arrows) consistent with focal fatty
infiltration.
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Variations of Pancreatic Contour
The head of the normal pancreas most often shows a smooth contour.
Sometimes, however, the healthy tissue in the pancreatic head and neck results
in unusual contours (Figs. 9A,
9B, and
9C), especially in the lateral
aspect (Figs. 10A and
10B), mimicking a pancreatic
neoplasm [8]. The attenuation
or signal intensity of the lobular pancreas producing these contour variations
is identical to the healthy pancreatic tissue on all images, including
unenhanced, arterial, and portal venous phase images. This is the key feature
that helps to differentiate this entity from a pancreatic tumor. Awareness of
the variations of the contour of the pancreatic head on cross-sectional images
is important to avoid diagnostic errors.
Fatty Replacement and Fat Sparing of the Pancreas
Fatty replacement of pancreas may be focal or diffuse. Focal fatty
replacement may simulate pathologic entities such as a neoplasm (Figs.
11A,
11B, and
11C). MRI and CT are useful
for confirming the presence of focal fatty infiltration and for
differentiating neoplasm from fat deposition and focal areas of fat sparing.
Complete pancreatic fatty replacement is commonly seen in patients with cystic
fibrosis (Fig. 12), with a
reported incidence of 56-93% in those patients.
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Fig. 12 —36-year-old woman with cystic fibrosis. Axial CT scan shows
complete fatty replacement of pancreas (arrows) anterior to splenic
vein (V). Liver (L) is noted. Splenic vein enlargement and splenomegaly (Sp)
are manifestations of portal hypertension.
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Pancreatic Cysts
Congenital pancreatic cysts are often incidentally detected. Such cysts are
asymptomatic and have a thin wall. Some pancreatic cysts may be associated
with von Hippel-Lindau disease (Fig.
13). These cysts are variable in size and may lead to cystic
replacement of the gland.
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Fig. 15 —52-year-old man with cirrhosis. Coronal thick-slab MR
cholangiopancreatography (MRCP) image shows loop (arrows) of
pancreatic duct in pancreatic head. Common bile duct (CBD), pancreatic duct
(P), and duodenum (D) are noted.
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Variations of Pancreatic Ducts
The pancreatic duct system shows a wide spectrum of anatomic variations,
both in the configuration of the ducts and in the manner in which the ducts
enter the duodenum [1]. A bifid
pancreatic duct (Figs. 14A and
14B) is an anomaly in which
the main pancreatic duct is bifurcated along its length. Multiple small
accessory pancreatic ducts are not rare; at times, the accessory pancreatic
duct forms a loop in the pancreatic head
(Fig. 15).
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Abstract
Introduction
