What is a pheochromocytoma?
Preganglionic sympathetic fibers synapse in the adrenal medulla. Under normal circumstances, this neuroendocrine tissue produces approximately 80% epinephrine and 20% norepinephrine, which function as hormones instead of neurotransmitters.
Most pheochromocytomas are adrenal medullary tumors, although a small percentage appear in the spleen, ovary, bladder, and right atrium. They usually arise from chromaffin cells, although 6% arise from other neuro-endocrine tissue. These tumors usually secrete more nor-epinephrine than epinephrine, similar to the normal tissue. Infrequently, pheochromocytomas secrete predominantly epinephrine or dopamine. They may occur independently or as part of a multiple endocrine neoplastic (MEN) syndrome .