Ganglioneuroma is a tumor of the peripheral nervous system. A person with a ganglioneuroma has a tumor that forms in the nerves outside the brain and spinal cord. A ganglioneuroma may form near the brain or spinal cord, or in the chest or abdomen. Ganglioneuromas are very rare, and most are not cancerous. These tumors may secrete hormones that may cause diarrhea, sweating, or excessive growth of body hair.