Ganglioneuroma in the Adrenal Gland of a Rat.

Necropsy was performed on a 22-month-old male Fischer 344 rat (Rattus norvegicus) that had weight loss and was icteric. Examination revealed a large, smooth, circumscribed, tan mass located at the cranial border of the right kidney. Microscopically, the mass consisted almost entirely of well-differentiated ganglion cells mixed with satellite and Schwann cells within a neurofibrillar matrix. The cells displaced the adrenal medulla and were partially surrounded by a thin rim of compressed adrenal cortex. Focal areas of hemorrhage and infiltrates of leukemic mononuclear cells were evident throughout the mass, but pheochromocytes were not detected. On the basis of findings during histologic examination, a diagnosis of adrenal medullary ganglioneuroma was made. Mononuclear cell leukemia was also diagnosed in the adrenal gland and was evident in lymphoid organs such as the spleen and mesenteric lymph nodes. Ganglioneuroma is rarely seen in rats and can be differentiated from more common complex pheochromocytomas, which consist of fewer neural components (< 80% of the mass). In rats, ganglioneuromas can develop in the central nervous system, pituitary gland, and thyroid gland. Differential diagnoses for a primary neoplasm of the adrenal gland should include carcinomas and adenomas of the adrenal cortex, and pheochromocytomas, neuroblastomas, and ganglioneuromas of the adrenal medulla.