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 .
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