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1 Department of Radiology, 4245 Roosevelt Way NE, Box 354755, University of
Washington, Seattle, WA 98105-6008.
2 Department of Radiology, Mayo Clinic College of Medicine, Scottsdale,
AZ.
Received March 1, 2006;
accepted after revision March 1, 2006.
Address correspondence to F. S. Chew.
Abstract
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Keywords: abdominal imaging • cystic lesions • intraductal pancreatic lesions • intraductal papillary mucinous neoplasm • pancreas
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| QUESTION 1 Which entity is most difficult to diagnose using MR cholangiopancreatography (MRCP)?
QUESTION 2 Which feature of pancreatic pseudocyst on CT suggests secondary infection?
QUESTION 3 Which imaging technique or procedure is most specific for differentiating a mucinous cystic tumor from a microcystic adenoma?
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Solution to Question 1
MR cholangiopancreatography is relatively unhelpful in the diagnosis of
acute pancreatitis [1]. In
acute pancreatitis, the duct is usually of normal caliber with a smooth wall.
Option C is the best response. MRCP is a powerful tool for evaluating
the pancreatic duct. Ductal anatomy and, thus, congenital anomalies and ductal
injury are well shown on MRCP. Pancreatic adenocarcinoma arises in the ducts.
Ductal dilatation with an abrupt cutoff is often seen with adenocarcinoma.
IPMN produces mucin that dilates the main and side pancreatic branches.
Solution to Question 2
Gas formation in a pseudocyst suggests secondary infection
[2]. However, previous internal
pseudocyst drainage or fistula formation may result in the presence of gas
without infection. Option B is the best response. The walls of chronic
pseudocysts may calcify, and the presence of calcification does not signify
infection. Heterogeneous attenuation of the contents of a pseudocyst may occur
with hemorrhage or necrosis. Enhancement of the cyst wall after IV contrast
injection is typical for a pseudocyst; the cyst will be uniformly thin.
Pseudocysts may extend outside of the pancreas or even be wholly outside
it.
| QUESTION 4 Which is the most common functioning islet cell tumor?
QUESTION 5 Which CT finding most strongly suggests the diagnosis of IPMN?
QUESTION 6 CT findings predictive of the presence of invasive carcinoma in the setting of IPMN include which of the following?
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Solution to Question 3
The presence of mucin within a percutaneously biopsied cyst is highly
specific for a mucinous tumor. Mucin is not present in microcystic adenomas
[2]. Option B is the
best response. Mucinous cystic tumors and microcystic adenomas have a variable
appearance on all forms of imaging. Cysts can be single or multiple in both
entities. Microcystic adenomas tend to have cysts smaller than 2 cm in
diameter, but larger cysts that would be more typical of mucinous cystic
tumors can occur. Both lesions can calcify. A calcified central scar would be
most typical of a microcystic adenoma. Calcification in the cyst walls would
be more typical of mucinous cystic tumor. On CT, both entities can have an
attenuation near that of water.
Solution to Question 4
The most common functioning islet cell tumor is an insulinoma
[2]. Option E is the
best response. The second most common functioning islet cell tumor is a
gastrinoma. Glucagonoma, somatostatinoma, and VIPoma are less common.
Insulinomas are usually small, hypervascular lesions that may contain
calcification. Large insulinomas are more likely to be malignant. Key facts
about insulinomas can be remembered by the "Rule of 10s": 10% are
multiple, 10% are malignant, and 10% are hyperplastic as opposed to
neoplastic.
Solution to Question 5
The CT appearance of IPMN is variable but generally involves intraductal
mucin globs or cystic masses causing obstruction. Obstruction leads to
dilatation and may result in fibrosis, parenchymal atrophy, and dysmorphic
calcification. Option B is the best response. Fatty replacement of the
pancreas is a characteristic finding in cystic fibrosis. Pseudocyst and
fistula formation are typically found in chronic pancreatitis. Multiple cystic
lesions involving the pancreas, liver, and kidneys suggest autosomal dominant
polycystic kidney disease [2,
3]. Diffuse parenchymal
calcification has not been described in IPMN.
Solution to Question 6
In a retrospective study of 36 patients with a pathologically proven
diagnosis of IPMN, features on presurgical MDCT were reviewed in an effort to
predict the presence of invasive carcinoma. The authors found that the
presence of a solid mass and main pancreatic duct involvement were highly
sensitive signs for the presence of invasive carcinoma in IPMN. Option
D is the best response. The presence of calcification was not predictive.
A unilocular cystic appearance was not associated with invasive carcinoma. The
common duct is not involved in IPMN. Lymph node enlargement was not associated
with invasive carcinoma
[4].
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