Serous Microcystic Adenomas

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In 1978, Compagno et al. described microcystic adenomas as composed of innumerable tiny cysts [2]. Serous microcystic adenoma is the most common subtype of SCT, accounting for more than 70% of SCTs [19, 20]. Synonyms include microcystic adenoma, glycogen-rich adenoma, and simply serous cystadenoma [1, 2, 10].

Females are more commonly affected (70%). Tumors usually affect elderly individuals in their 6th and 7th decades (34-91 years). The patients may present with a palpable mass or vague abdominal pain. Asymptomatic cases have been found incidentally during imaging techniques, at laparotomy or at autopsy. Serous microcystic adenoma is a slow-growing tumor and it can become large

Fig. 1. Serous microcystic adenoma. Enhanced CT scan shows well-defined cystic lesion in the pancreatic tail. Note the central stellate scar.

enough to compress adjacent structures [10]. The tumors may occur in any part of the pancreas but have some predilection for the head. When located in the head of the pancreas, these tumors can compress the common bile duct and result in jaundice. Gastrointestinal hemorrhage and pancreatic duct obstruction have been reported [21]. Rare cases co-exist with other pancreatic neoplasms, such as pancreatic ductal adenocarcinoma and islet cell tumor [22-25]. Ultrasonography (US) and computed tomography (CT) show characteristic multiple small loculations. A central scar with 'sunburst' calcification is evident in some patients (fig. 1). Most cases are solitary, but in rare cases the tumor is multicentric [26, 27]. Compagno and Oertel report three cases which involved the entire pancreas and four cases which were found in the body and tail [2]. Association of SCT with von Hippel-Lindau (VHL) disease has been suggested [28]. VHL disease is an autosomal-dominant genetic disorder, characterized by the development of a variety of neoplasms.

Macroscopically, the diameter of the tumors is 1-25 cm (mean 6-10 cm). The tumors are spherical to ovoid, well-circumscribed masses. The distinctive feature of the tumor is its composition of many small cysts, which imparts a characteristic honeycomb-like cut surface. The cyst walls are paper-thin and translucent. The larger tumors often have a central stellate scar that is sometimes calcified and from which fine fibrous septa radiate to the periphery (fig. 2). The individual cysts are usually a few millimeters but some may be a few centimeters in size. The cysts contain clear serous fluid, with a low CEA level. No necrosis is noted.

Microscopically, the tumors are composed of multiple small cysts, which vary in size and shape (fig. 3) [10]. A micro-glandular pattern and a pattern

Normal Pancreas Cut Surface
Fig. 2. Serous microcystic adenoma. The cut surface discloses a honeycomb mesh-work of numerous small cysts and a central stellate scar.
Fig. 3. Serous microcystic adenoma. Characteristic spongy appearance as a result of numerous cysts, which vary in size and shape. The tumor is well demarcated from the adjoining pancreatic tissue by a small fibrous band.

consisting of larger cysts are usually admixed. The cysts are lined by a single layer of small, flat to cuboidal cells (fig. 4). Some foci of the tumors may show low-papillary patterns, covered by cytologically bland epithelium (fig. 5) [29]. The tumor cells have clear to pale cytoplasm due to their abundant glycogen

Fig. 4. Cysts are lined by a single layer of flattened epithelial cells with clear cytoplasm and well-defined cell margins. The nuclei are dark and centrally located. Note the thin underlying fibrous cyst wall.

Fig. 5. Some tumor areas show a tendency to papillary tufting with a fibrovascular core.

content. Because of the presence of intracytoplasmic glycogen, Periodic acid-Schiff (PAS) staining is positive, and staining for PAS after diastase treatment is negative (fig. 6). In rare cases, the cytoplasm is eosinophilic and granular. They have only an insignificant amount of mucin. The nuclei are small, round-to-ovoid, somewhat hyperchromatic. Mitotic activity, cytological atypia and nuclear pleomorphism are absent. The cysts are separated by thin fibrous tissue,

Fig. 6. PAS stain demonstrating large amounts of cytoplasmic glycogen (a), which is removed by diastase pretreatment (b).

which has numerous blood vessels. The prominent vascularization of these tumors can be appreciated by angiography. The trabeculae between the cysts may also show calcification, which appears as a radiating pattern radiographi-cally. The trabeculae may contain entrapped Langerhans islets at the periphery of the tumor. An incomplete fibrous pseudocapsule separates the tumors from the adjacent pancreas. The characteristic cytology of SCT is that of cellular sheets of low cuboidal cells, clear cytoplasm, and intranuclear cytoplasmic inclusions [1].

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