Incidentally detected giant oncocytoma arising in retroperitoneal heterotopic adrenal tissue.

A nonfunctional retroperitoneal oncocytoma incidentally discovered in a 40-year-old woman is described. The tumor, which was 17 cm in largest dimension, was completely separated from the kidneys and adrenal glands and consisted of nests of polygonal cells with large, granular, eosinophilic cytoplasm. Significant nuclear atypia, necrosis, and mitosis were absent. Ultrastructural analysis confirmed the oncocytic nature of the neoplastic cells. Since neoplastic cells were not immunoreactive for chromogranin and did not contain dense-core secretory granules, the diagnosis of oncocytic paraganglioma was excluded. Cells immunoreactive for 3beta-hydroxysteroid dehydrogenase, the enzyme catalyzing the conversions of pregnenolone to progesterone and dehydroepiandrosterone to androstenedione, were identified in the tumor, thus strongly indicating adrenocortical tissue origin. Multiple nests of 3beta-hydroxysteroid dehydrogenase-positive cells were detected in the loose retroperitoneal connective tissue. These findings strongly support the origin of the tumor from heterotopic retroperitoneal rests of the adrenal gland. To our knowledge, only 1 similar case has been described in the literature to date.