Pseudopapillary solid cystic tumor arising from an extrapancreatic site.

A case of pseudopapillary solid cystic tumor arising in the omentum of a 46-year-old woman is presented. A well-defined, encapsulated tumor measuring 5.2 x 4.0 x 4.0 cm was histologically characterized by a combination of solid and pseudopapillary growth patterns of tumor cells with abundant pale-to-eosinophilic cytoplasm. No pancreatic tissue was observed within or adjacent to the tumor. Immunohistochemically, the tumor was positive for vimentin, epithelial membrane antigen, and alpha1-antichymotrypsin. Ultrastructurally, the tumor cells contained electron dense granules of variable sizes, most likely representing lysosomes. Flow cytometry showed a diploid DNA content with a high S-phase fraction. The patient was well without recurrence 3 months after diagnosis. It is important to include pseudopapillary solid cystic tumor in the differential diagnosis of omental tumors.