Metastatic adult granulosa cell tumor mimicking a benign pancreatic cyst.

We report an unusual case of metastatic adult granulosa cell tumor in the head of pancreas mimicking a benign pancreatic cyst in a 43-year-old female. Clinically, it was considered a benign cyst of the pancreas based on its appearance by imaging and that repeated fine-needle aspiration and cytologic examination of cystic fluid failed to identify malignant cells. The cyst in her pancreas grew slowly during the 15 months of close follow-up. Subsequent drainage and open biopsy of the cyst wall established the diagnosis of metastatic adult granulosa cell tumor that was confirmed in pancreaticoduodenectomy specimen. Immunohistochemical study and clinical history were critical to make the correct diagnosis and to differentiate this tumor from other more commonly encountered cystic neoplasms of the pancreas.