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EDUCATION EXHIBIT |
Department of Radiologic Pathology, Armed Forces Institute of Pathology, Washington, DC, Department of Radiology and Nuclear Medicine, Uniformed University School of Health Science, Bethesda, Md
Department of Radiology, Brigham and Women’s Hospital and Harvard Medical School, Boston, Mass
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Commentary |
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The variable nomenclature for this tumor has led to considerable diagnostic confusion and is indicative of its diverse radiologic and histologic manifestations. The distribution of the tumor can be local or diffuse; it may involve the main pancreatic duct or branches, and histologically, it ranges from benign to malignant. The past nomenclature can also be confused with the more common terms "ductal adenocarcinoma of the pancreas" and "mucinous cystic neoplasm." The correct diagnosis of this tumor is prognostically significant because IPMT has a more favorable prognosis in comparison with ductal adenocarcinoma of the pancreas.
IPMT typically manifests in patients in the 7th decade of life. Symptoms may include vague abdominal pain, nausea, diarrhea, steatorrhea, and jaundice. Pancreatitis or pancreatitis-like symptoms may be present if there is complete or partial duct obstruction. Some patients may be asymptomatic, particularly if the tumor is in the tail of the pancreas. IPMT is more frequently found in the head or body of the pancreas and is more common in men (1),(2),(6),(7). Histologically, there is intraductal epithelial proliferation of mucin-producing cuboidal or tall columnar cells. The abundant mucin production creates ductal dilatation.
The cells are in a papillary or cribriform configuration in ectatic or cystically dilated main or branch pancreatic ducts. There may be varying degrees of cytoarchitectural atypia, comedo-type necrosis, and sialomucin production (7),(8). Foci of hyperplasia (with or without atypia or dysplasia), carcinoma in situ, and invasive carcinoma may be present in a single tumor. Thus, the degree of cytoarchitectural atypia may vary from case to case and in the same tumor (5). IPMT is not clearly classified as benign or malignant. Therefore, some authors have proposed that all of these tumors should be considered to have low-grade malignant potential (7).
In this issue of RadioGraphics, Lim et al illustrate the radiologic spectrum of IPMT, adding to the increased interest in and awareness of this entity. To our knowledge, they are only the second group of investigators to acknowledge and display the spectrum of radiologic appearances. Lim et al emphasize, as have others in the recent literature (1),(9)–(11), the limitations of cross-sectional imaging in the diagnosis of IPMT. Demonstration at ERCP of communication between a cystic lesion and the pancreatic duct or filling defects in the main pancreatic duct or side branch have been described as the most specific finding. There is mounting evidence in the literature, however, that the diagnosis can be made with thin-section CT or MRCP (9),(12)–(15).
When the findings of a bulging papilla, papillary projections in the ducts, or communication of the main pancreatic duct with a cystic lesion are present at CT or MRCP, the diagnosis can be made without invasive ERCP. Therefore, we would like to diverge from the opinion of Lim et al that ERCP is the procedure of choice for the diagnosis of IPMT. ERCP should be used in cases where the diagnosis is not clear at imaging.
Lim et al describe three morphologic patterns of IPMT: branch duct type, main duct type, and combined type. It should be noted that the main duct type may be focal or diffuse, and the branch duct type may have cystic side branches or dilated side branches (5),(16). Familiarity with the varied appearances and patterns of IPMT is crucial to its radiologic diagnosis (Figure).
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Footnotes |
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The opinions and assertion contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Departments of the Army or Defense.
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Department of Radiology, Samsung Medical Center, Seoul, Korea
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Response |
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Regarding the role of cross-sectional imaging such as CT and MRCP versus ERCP, they stressed the relative importance of noninvasive thin-section CT and MRCP in the demonstration of bulging papilla, papillary projections in the pancreatic duct, and communication of the cyst with the pancreatic duct.
Bulging papilla into the lumen of the duodenum are encountered not only in IPMT but also in choledochal cyst (choledochocele); therefore, the finding is not characteristic of IPMT. Intraluminal papillary projections or mass in the dilated main pancreatic duct or branch duct is also a very convincing sign of IPMT. These two findings can be well visualized with thin-section CT. When they are visualized in association with characteristic dilatation of the main pancreatic duct or branch ducts, diagnosis is confident. The frequency of bulging papilla in IPMT is not high, however, being encountered in 22% of cases (1). In my experience and that of others (1), an intraluminal papillary mass is usually small and flat and thus difficult to detect.
Communication of the main pancreatic duct with a cystic lesion, although not conclusive, is an important finding in establishing the diagnosis of IPMT. Theoretically and practically, however, direct communication of a cystic lesion and the pancreatic duct is impossible to demonstrate with CT and MRCP. A cyst abutting or close to the pancreatic duct may look like a communication with the pancreatic duct at CT and MRCP. Mere contact of two lumina or cystic spaces at cross-sectional imaging is often considered communication in the radiology literature (1)–(5), but in fact, that is not true. We have several cases of noncommunicating neoplastic cysts or pseudocysts that we thought communicated with the pancreatic duct at thin-section (3 mm) CT or MRCP. Furthermore, communication with the pancreatic duct is not specific for IPMT because mucinous cystic neoplasm and pseudocyst frequently communicate with the pancreatic duct.
Therefore, ERCP is the most important modality, not only in the demonstration of intraductal tumor and communication of a cystic lesion with the typically dilated pancreatic duct for diagnosis, but also in the delineation of pathologic anatomy of pancreatic ductal dilatation for the planning of surgical resection. Additional crucial information available at ERCP is direct visualization of bulging papilla and demonstration of mucus protruding through the patulous papilla of Vater.
Morphologic patterns illustrated by Drs Levy and Ros are very informative. They classified the main duct type of IPMT as diffuse or focal and branch duct type as cystic or dilated side branches. In my opinion, cystic or simple dilatations of the side branches may be a matter of descriptive terms rather than different types.
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