AJR 2001; 176:179-185
© American Roentgen Ray Society
Intraductal Papillary Mucinous Tumors of the Pancreas
Anne M. Silas1,
Martina M. Morrin,
Vassilios Raptopoulos and
Mary T. Keogan
1
All authors: Department of Radiology, Beth Israel Deaconess Medical Center,
330 Brookline Ave., Boston, MA 02215.
Received May 11, 2000;
accepted after revision June 28, 2000.
Address correspondence to M. T. Keogan.
Introduction
The term "intraductal papillary mucinous tumor of the pancreas"
has been introduced as a unifying label for mucin-producing pancreatic
neoplasms previously referred to as papillary and villous adenomas, mucinous
duct ectasia, and mucin-producing adenomas and carcinomas with or without
invasion. Unique clinical, radiologic, and pathologic characteristics of
intraductal papillary mucinous tumors of the pancreas have been described
[1]. Radiologic examination is
necessary for treatment planning because imaging features may indicate the
site of tumor origin in the pancreas in addition to extent of spread.
Clinical Features
Intraductal papillary mucinous tumors of the pancreas are observed
predominantly in men between 60 and 80 years old and occur most often in the
pancreatic head [2]. Small
intraductal tumors are typically discovered incidentally at cross-sectional
imaging performed for other indications. The nonspecific and indolent nature
of presentation often delays accurate diagnosis
[2,
3]. Presenting symptoms of
larger tumors mimic those of chronic pancreatitis, particularly episodic
epigastric pain occasionally radiating to the back. Additional signs and
symptoms of advanced disease include abdominal mass, diarrhea, diabetes, and
weight loss. Intraductal papillary mucinous tumors have a low potential for
malignancy, and multiple clinicopathologic reviews of these tumors reveal slow
growth rates, rare parenchymal invasion, and low rates of metastatic spread
and recurrence after resection
[4]. Preoperative diagnosis is
based on clinical presentation and characteristic imaging findings. The role
of cytologic analysis has not been defined. The low but definite potential for
malignancy of these lesions implies that surgical resection is the preferred
method of treatment [2].
Pathology
Intraductal papillary mucinous tumors (IPMTs) of the pancreas arise in the
pancreatic ducts and have been described in all pancreatic duct segments
[5]. Tall mucin-producing
columnar epithelial cells lining the pancreatic ducts become hyperplastic and
subsequently dysplastic. The dysplastic cells proliferate and form papillary
projections that protrude into and expand the pancreatic duct, remaining
isolated in either the main pancreatic duct or branch ducts or extending from
one portion of the pancreatic ductal tree to another
[3]. Duct obstruction may be a
result of tenacious mucin plugs or ductal compression by cystic masses
(Fig. 1). Long-term obstruction
of the main pancreatic duct leads to atrophy and fibrosis mimicking chronic
pancreatitis.
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Fig. 1. —77-year-old man with epigastric pain. Coronal MR
cholangiopancreatogram (TR/TE, 2800/1100) shows cystic dilatation of
side-branch duct within uncinate process. Note large filling defect that
represents mucin plug (arrow).
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IPMT is classified into main and branch duct types
[6] (Fig.
2A,2B,2C,2D).
Side-branch duct involvement alone (Fig.
3) is typically associated with benign adenomas manifesting as
localized cystic parenchymal lesions. Main pancreatic duct involvement alone
presents as diffuse ductal dilatation, gross mucin production, and
micropapillary studding (Fig.
4A,4B),
and is typically associated with malignancy
[7].
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Fig. 2A. —70-year-old man with chronic abdominal pain. Axial
contrast-enhanced CT scans show dilated main pancreatic duct (MPD) and cystic
dilatation of side-branch ducts (SB) in pancreatic head.
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Fig. 2B. —70-year-old man with chronic abdominal pain. Axial
contrast-enhanced CT scans show dilated main pancreatic duct (MPD) and cystic
dilatation of side-branch ducts (SB) in pancreatic head.
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Fig. 4B. —77-year-old man with jaundice. Endoscopic retrograde
cholangiopancreatogram corresponding to A reveals narrowed main
pancreatic duct with upstream duct dilatation and filling of single cystic
lesion. Large cystic lesion visualized on CT scan is not opacified. Note
malignant transformation was seen in resected specimen but could not be
inferred from pre-operative imaging findings.
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The presence of malignancy and degree of invasion cannot be reliably
determined pre-operatively by imaging (Fig.
4A,4B)
or cytologic analyses. However, MR imaging features of malignancy, including
filling defects, diffuse main duct dilatation larger than 15 mm (main duct
type), or segmental duct dilatation (branch duct type) have been suggested
[6]. Intraoperative diagnosis
of malignancy and determination of surgical margins is achieved by frozen
section analysis.
Imaging
CT
CT is often the initial modality with which IPMT is suspected or diagnosed,
although clinical and imaging findings of chronic pancreatitis may obscure the
correct diagnosis. Dysmorphic calcifications may be seen in mucinous
collections in the dilated main pancreatic duct. Grapelike clusters of
involved side-branch ducts may also be revealed. Thin-section
contrast-enhanced CT and multiplanar reconstructions may best reveal
communications between cystic dilated segments and the main pancreatic duct
(Fig.
5A,5B,5C).
Mucin globs and gaping papillae may be seen as filling defects within the
dilated ducts and duodenal lumen, respectively
(Fig. 6). Septa and excrescent
nodules seen along the dilated duct have been described as a feature of the
main pancreatic duct type of IPMT on CT.
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Fig. 5A. —43-year-old man with symptoms of pancreatitis. Axial
high-resolution contrast-enhanced CT scan (A) and CT oblique
reconstruction (B) show cystic lesion contiguous with prominent main
pancreatic duct.
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Fig. 5B. —43-year-old man with symptoms of pancreatitis. Axial
high-resolution contrast-enhanced CT scan (A) and CT oblique
reconstruction (B) show cystic lesion contiguous with prominent main
pancreatic duct.
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Endoscopic Retrograde Cholangiopancreatography
Endoscopic retrograde cholangiopancreatography (ERCP) was previously
considered the gold standard for evaluation and diagnosis of IPMT lesions
[3], although in contrast with
MR imaging, the entire pancreatic ductal system may not be visualized with
ERCP [6] (Fig.
7A,7B,7C,7D).
On ERCP, real-time visualization of the patulous ampulla of Vater and abundant
mucus production is diagnostic of this condition. Additionally, main
pancreatic duct dilatation in the absence of proximal stricture and filling
defects caused by mucus plugs in the pancreatic duct and communicating cystic
lesions may be revealed on ERCP
[6].
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Fig. 7A. —72-year-old man with chronic pancreatitis. Endoscopic
retrograde cholangiopancreatogram reveals dilated distal main pancreatic duct
with communicating cystic lesion (arrow). Proximal main pancreatic
duct is not seen.
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Fig. 7D. —72-year-old man with chronic pancreatitis. MR
cholangiopancreatogram (2800/1100) shows full extent of diffuse disease
involving distal main pancreatic duct (wavy arrows) and side-branch
ducts (straight arrows).
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MR Imaging and MR Cholangiopancreatography
The high sensitivity to soft-tissue contrast and the multiplanar capability
inherent in MR imaging enables visualization of the bile and pancreatic duct
systems, thereby allowing identification of small clusters of dilated lateral
side branches as well as the entire main pancreatic duct. MR imaging can
reveal areas of ductal stenosis and dilatation, extent of associated cystic
lesions, and communications between these cystic lesions and the ductal
system. MR imaging is now considered superior to ERCP given the ability of MR
imaging to reveal the full extent of ductal involvement, particularly when
obstructing mucus prevents diagnostic opacification of the entire duct (Fig.
7A,7B,7C,7D).
Filling defects caused by mucin and papillary projections may be shown
[8]
(Fig. 8). Standard anatomic
imaging (T1- or T2-weighted) may also be performed to look for evidence of
local spread (Fig.
9A,9B).
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Fig. 9B. —77-year-old woman with weight loss. Axial T2-weighted MR
image (4.4/64)at same level as A shows high signal of innumerable
dilated side-branch duct cysts (arrows) emanating from normal-caliber
proximal main pancreatic duct. No surrounding adenopathy is seen.
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CT and MR imaging serve as adjuncts to the more invasive ERCP by revealing
pancreatic masses and associated inflammatory changes, adenopathy, and
metastatic disease, in addition to any associated vascular stenoses,
thromboses, and occlusions.
Sonography and Intraoperative Sonography
Sonography may readily reveal one or multiple cystic pancreatic masses or
ductal dilatations; however, echogenic mucin may make the tumor
indistinguishable from the surrounding pancreatic parenchyma (Fig.
10A,10B,10C).
Intraoperative sonography affords superior visualization of the
pancreaticobiliary system and facilitates identification of cystic lesions and
mural nodules (Fig.
11A,11B).
Conclusion
IPMTs of the pancreas should be considered in the differential diagnosis of
cystic pancreatic tumors with or without ductal dilatation and in the
differential diagnosis of chronic pancreatitis. The diagnosis is suggested
primarily by ERCP and MR imaging findings, although imaging may not reliably
reveal the presence of malignancy. Because these tumors have malignant
potential, surgical excision with frozen section analysis is advocated,
followed by surveillance imaging.
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Introduction
Clinical Features
