Case 5 -

Intraductal Papillary Mucinous Neoplasm Martha Bishop Pitman Harvard Medical School and Massachusetts General Hospital Boston, MA

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Clinical History A 75 year old alcoholic woman presented with abdominal pain. Ultrasound revealed a 4 cm multiloculated cystic mass in the head of the pancreas connected with a dilated pancreatic duct. The cyst had thick septations and there was no apparent wall mass. An endoscopic ultrasound guided biopsy was performed. 30cc of viscous mucoid fluid was aspirated and sent for cytological evaluation and cyst fluid analysis. A cytospin slide was prepared and stained with a Papanicolaou stain. Case 5 - Figure 1 - The smear background displayed thick "colloid-type" mucin containing scattered epithelial cells, inflammatory cells and histiocytes (Low power, Papanicolaou stain). Case 5 - Figure 2 - Some of the epithelial cells were in small, cohesive sheets with small round uniform nuclei and ample clear to vacuolated cytoplasm consistent with "adenoma" type epithelium (Medium power, Papanicolaou stain). Case 5 - Figure 3 - Other epithelial cells were single and resembled high grade cervical dysplasia with atypical convoluted and hyperchromatic nuclei and a high nuclear to cytoplasmic ratio consistent with at least borderline malignancy(High power, Papanicolaou stain). Cytological Findings: The specimen background contained thick viscous, colloid-like mucin. Histiocytes and a few inflammatory cells were also present in the mucin, but an acute inflammatory, bloody or bile stained debris field was not present. Glandular epithelial cells were seen singly, in small flat groups, and one large monolayered sheet was present. Some cells were degenerated and necrotic but many viable cells demonstrated atypia. Single small cells displayed features of high-grade dysplasia, similar to what you would see in high-grade dysplasia of the cervix. A large sheet of cells showed nuclear crowding, chromatin clearing, mildly irregular nuclear membranes and nuclear grooves Cytological Diagnosis: Neoplastic mucinous cyst with at least moderate dysplasia (borderline malignancy) consistent with IPMN. Invasion cannot be determined from this specimen. Histological Findings: A Whipple procedure removed the pancreatic head that demonstrated a multiloculated cystic mass in continuity with the pancreatic duct. Histologically the cysts were lined by papillary mucinous glandular epithelium with variable atypia ranging from totally bland (adenoma-like) to moderate dysplasia (borderline malignancy) and focally with atypia consistent with carcinoma in-situ. The pancreatic duct and a major branch were involved. No subepithelial ovarian-like stroma was present. Unequivocal invasion of the cyst wall was not identified. Histological Diagnosis: Intraductal papillary mucinous neoplasm (combined type), predominantly with moderate dysplasia (borderline malignancy) but with focal intraductal carcinoma. Discussion: Although the history of alcoholism raised the clinical differential diagnosis of a pseudocyst, the aspiration of thick, viscous mucoid fluid and cytologically, the presence of thick colloid type background mucin defines the cyst as a mucinous cyst. Although an obstructed duct and retention cyst can contain mucin, these causes of a mucinous cyst are relatively rare, neither likely to be 4 cm in size. GI contamination can be in the form of both mucin and epithelium, but GI mucin is not so abundant as to cover the slide like colloid (see discussion below). The presence of the dysplastic epithelial cells is a feature of at least borderline malignancy. The cytology alone defines a neoplastic mucinous cyst of at least borderline malignancy. The cyst fluid CEA of 850 ng/ml support that interpretation, and the cytology combined with the clinical and radiological findings allows for an interpretation of "consistent with IPMN". Neoplastic mucinous cysts include two distinct neoplasms: intraductal pancreatic mucinous neoplasm (IPMN) and mucinous cystic neoplasm (MCN). Intraductal papillary mucinous neoplasm (IPMN) These tumors represent a defined clinicopathological entity composed of a typically papillary intraductal epithelial proliferation showing a spectrum of atypia ranging from benign to malignant. IPMN, a.k.a. mucinous cystadenoma or cystadenocarcinoma, papillary adenomas, villous adenomas, intraductal mucin-hypersecreting neoplasm, papillary cystadenoma and cyst adenocarcinoma, and mucin-producing tumor or carcinoma, was first recognized as a distinct entity by Ohhashi, et.al. in 1982, and since then this entity has been increasingly recognized. It is now estimated that IPMNs account for 3 to 5% of all pancreatic neoplasms, and 20% of cystic neoplasms of the pancreas. These neoplasms occur primarily in elderly patients, are more common in men in most studies, although at MGH there is a female predominance, and they occur primarily in the head and body of the pancreas. By definition, these cysts connect with the pancreatic ducts. There are three subtypes: main duct, side branch and combined. The main pancreatic duct may be markedly dilated, and may contain multiple cysts, usually > 1cm and typically between 3 and 5cm, that may involve the entire length of the main pancreatic duct, segments of the main pancreatic duct or branches of the pancreatic duct. Endoscopy may show a dilated and patulous Ampulla extruding mucin a feature which is virtually pathognomonic for IPMN. Histologically, the WHO categorizes the tumors according to the worst degree of atypia of the lining epithelium that may be very heterogenous: Intraductal papillary mucinous adenomas are lined by benign columnar mucinous epithelium. Intraductal papillary mucinous neoplasms with moderate dysplasia (synonymous with the term borderline neoplasm) show greater degrees of epithelial atypia characterized by pseudostratification of the cells, loss of mucin due to increased nuclear to cytoplasmic ratio and increased architectural complexity, e.g. tufting, cellular buds. Intraductal papillary mucinous carcinomas are neoplasms with in-situ carcinoma lining the villi and with no evidence of invasion of the cyst wall. The architectural complexity and cytological atypia are more severe than borderline tumors. Invasive papillary mucinous carcinomas are defined by a carcinoma breaching the integrity of the cyst wall. The invasive carcinoma is usually colloid type or mucinous noncystic carcinoma (50%) or tubular type (50%) and is seen in approximately 35% of cases. The presence or absence of an invasive carcinoma is the single most important prognosticator for patients with IPMN. An associated solid or gelatinous cyst wall nodule should suggest the presence of an invasive carcinoma. Small invasive carcinomas can arise focally in a large IPMN, even in the absence of a grossly defined stromal mass, and as such all IPMNs should be carefully examined and extensively sampled. Mucinous cystic neoplasm Mucinous cystic neoplasms account for approximately 5-6% of primary pancreatic neoplasm. They occur predominantly in middle-aged (40-50 year old) females in the body and tail of the pancreas. These neoplasms typically do not connect with the pancreatic duct which is not dilated. The cysts are lined by tall, columnar, mucin-producing epithelium that may be studded with neuroendocrine or Paneth cells. An ovarian-type stroma underlies the epithelium in most MCN. The W.H.O. has classified these neoplasms according to the degree of atypia of the cyst lining epithelium as: Mucinous cystadenoma: A cystic mucinous neoplasm lacking atypia of the lining epithelium Mucinous cystic neoplasm with moderate dysplasia (borderline): neoplasms showing dysplastic epithelial changes such as papillary infoldings, cellular stratification, crowding of nuclei and mitoses. Mucinous cystadenocarcinoma: Tumors in which the cyst lining is malignant. These may be further subclassified into invasive or non-invasive. Approximately one third of MCN will have an invasive component. Most of the invasive carcinomas are of the conventional tubular type, but undifferentiated carcinomas with osteoclastic-type giant cells and other rare malignancies including choriocarcinoma and sarcoma have been reported. Proper subclassification of MCN is frequently not accurate by cytology or biopsy alone. Due to the heterogeneity of the cyst lining epithelium and abrupt transition from benign to dysplastic to carcinoma, complete histological examination is warranted. Cytology of Neoplastic Mucinous Cysts The pre-operative diagnosis of pancreatic cysts is generally dependent on cytology that is increasingly being performed by EUS-FNAB. The cytological features frequently cannot distinguish these two entities and distinction requires clinical and radiological correlation. The required cytological components for a specific diagnosis of a neoplastic mucinous cyst in general include: Abundant, thick colloid-like mucin. Glandular epithelium +/- visible cytoplasmic mucin and +/- varying degrees of atypia. The cytoplasmic mucin is less apparent in borderline and in-situ neoplasms. The first clue that the cyst is mucinous is often at the time of aspiration of cyst fluid if the fluid is mucoid and viscous and does not readily pass into the needle, as in this case. Not all neoplastic mucinous cysts will demonstrate this however. Mucin that appears as a thick layer in the background of the smears and often contains histiocytes and cellular debris, is a feature that is helpful in distinguishing neoplastic mucin from GI contamination. Since not all neoplastic mucinous cysts will demonstrate abundant and obvious extracellular mucin, however, special mucin stains and cyst fluid analysis should be done in all cases that produce enough fluid for these ancillary tests. The degree of atypia in the epithelial groups in the cytology sample will depend upon the differentiation of the part of the neoplasm sampled. Adenomas: The glandular cells are arranged in flat sheets or as single cells and show a minimal amount of nuclear atypia. Nuclear grooves and inclusions may be seen. Borderline: The nuclei become larger with more hyperchromasia and some mitotic activity. The architecture of the groups becomes more complex, and shows cellular groups with crowding and overlapping of the nuclei. Small tight clusters of high N:C ratio cells may be all that is present. Inflammation is commonly present in the background. Intraductal carcinoma: Sheets of cells with features of well-differentiated adenocarcinoma, single malignant cells and mitoses are characteristic. Well-differentiated adenocarcinoma cells display pale nuclear chromatin similar to thyroid papillary carcinoma, nuclear grooves, irregular nuclear membranes, odd nuclear shape, subtle nuclear crowding and focal loss of nuclear polarity. Necrosis and inflammation are more often present than in lower grade neoplasms. Invasive carcinoma: The presence of invasion cannot be determined from the aspiration of a cyst alone. However, aspiration of a solid area in the cyst wall, when visualized by radiological guidance may prove diagnostic of adenocarcinoma when the cyst fluid is not. The most important question to answer when evaluating a cystic mass in the pancreas is: Is it a pseudocyst or not? That determination will decide the need for resection in most cases. Pseudocysts are the most clinically relevant since they are the most common, and most misdiagnoses occur when neoplasms are misdiagnosed as these benign, inflammatory cysts. Pseudocysts occur following bouts of acute pancreatitis from any cause when autodigested, necrotic parenchyma is walled off by an inflammatory response forming a cystic lesion composed of a fibrous wall and inflammation without an epithelial cyst lining. Alcoholism with pancreatitis is a common clinical setting. Aspiration of a pseudocyst typically retrieves an abundant amount of dark brown, turbid fluid. Cytological preparations are characterized by granular background debris and blood, occasionally bile or hematoidin pigment- but not mucin- and by an inflammatory cell population composed predominantly of histiocytes, which may contain hemosiderin, and neutrophils. The cyst fluid lacks cyst lining epithelial cells, but normal or metaplastic pancreatic epithelium, acini, islet cells, fibroblasts, gastrointestinal epithelium or mesothelial cells may all be inadvertently aspirated. Gastrointestinal contamination Gastrointestinal (GI) epithelium is a consistent, and occasionally abundant, contaminant in aspirates obtained with EUS FNAB. When abundant, the cellularity of the smear, combined with the architectural features and subtle nuclear abnormalities may lead to a false positive diagnosis, either well differentiated adenocarcinoma in the case of solid masses and neoplastic mucinous cyst with the aspiration of cystic masses. This latter differential diagnosis is the most difficult. Quality of the background mucin and its contents and evaluation of cellular architecture and nuclear features of the epithelium are helpful in most cases but not all (Nagle and Pitman, unpublished data). Thick colloid-like mucin defines neoplastic mucin and is not GI contamination, as discussed above. Scant to moderate amounts of thick and thin mucin on a slide could be either GI contamination or neoplastic cyst contents. Duodenal epithelium usually appears as large folded sheets of uniformly distributed round regular nuclei with smooth nuclear membranes and inconspicuous nucleoli. Goblet cells are a helpful distinguishing feature. A luminal edge may also be present demonstrating non-mucinous epithelium (barring the presence of foveolar metaplasia in peptic injury). Gastric epithelium is often present in smaller cell clusters and sheets and may well appear mucinous, but usually as a small apical cup of mucin rather than diffusely involving the cytoplasm. When you consider that adenomas of either type of neoplastic mucinous cyst are not likely to yield a highly cellular aspirate just by the histology of the cyst (IPMN>> MCN), and this has been our experience, then any smear containing abundant glandular epithelium is likely GI contamination. Cyst Fluid Analysis Cyst fluid analysis is helpful in many cases. CEA and amylase are the two markers routinely performed on aspirated cyst fluid at MGH. Other tumor markers have been studied. Pseudocysts are characterized by high amylase (usually greater than 5,000 U/L) and low CEA (<200 ng/l). Neoplastic mucinous cysts generally have a high CEA (>200 ng/ml). The amylase will be low in MCN and high in IPMN given the continuity of the cyst with the ductal system for IPMN. A recent study in our department showed that cyst fluid CEA levels > 500 ng/ml and/or CA19.9 levels > 5000 U/ml strongly supported a diagnosis of a malignant pancreatic mucinous cyst, and that a CEA > 500 ng/ml and a CA125 > 50 U/ml in the context of a pancreatic mucinous cyst suggests a diagnosis of an IPMN (Michaels and Pitman, unpublished data). Although CEA remains the single best predictor of cyst type, it may be helpful to continue to analyze cyst fluid for these other markers. References Albores-Saavedra J, Gould EW, Angeles-Angeles A, et al. Cystic Tumors of the Pancreas. Pathology Annual, 1990. 25(pt. 2): p. 19-50. Brugge WR, Lewandrowski K, Lee-Lewandrowski E, et al. Diagnosis of pancreatic cystic neoplasms: a report of the cooperative pancreatic cyst study. Gastroenterology, 2004. 126(5): p. 1330-6. Centeno BA, Warshaw AL, Mayo-Smith W, et al. Cytological diagnosis of pancreatic cystic lesions: A prospective study of 28 percutaneous aspirates. 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