Retroperitoneal cystic neuroendocrine tumor. A case report.

: A 21 cm retroperitoneal cystic mass was excised from a 71 year old woman. The cyst was filled with a hemorrhagic fluid and contained a 5 cm parietal hemorrhagic nodule. On histology, the nodule was composed of a uniform population of round cells arranged in trabeculae and nests. The neoplastic cells were immunoreactive to cytokeratin, EMA, NSE, chromogranin A, pancreatic polypeptide (PP) and Gastrin (G). Ultrastructural observation of neurosecretory granules confirmed the neuroendocrine nature of the tumor. No other lesions were detected and a diagnosis of primary epithelial neuroendocrine tumor was rendered. The histogenesis of the tumor including the possibility of a paraganglionic origin is discussed.