Functional vs non-functional
An endocrine tumor is a growth of hormone-producing tissue. The crucial split is whether it secretes. A functional tumor makes hormone autonomously — it ignores the feedback that should switch it off — so the patient presents with a hormone-excess syndrome, often while the tumor is still tiny. A non-functional tumor is silent hormonally and only causes trouble by its bulk: pressing on nearby structures, or turning up by surprise on a scan as an incidentaloma.
A field guide to the classic offenders
Each functional tumor announces itself through the hormone it overmakes. A prolactinoma floods the body with prolactin, causing milk discharge and, by suppressing the gonadal axis, infertility and low libido. A pheochromocytoma of the adrenal medulla dumps catecholamines in surges, producing pounding headaches, sweating, and dangerous spikes of blood pressure. A growth-hormone-secreting pituitary adenoma causes acromegaly — the slow coarsening of hands, feet, and face in adults.
A whole family arises from the diffuse hormone-producing cells of the gut and lung — the neuroendocrine tumors. When such a tumor secretes serotonin and other mediators that reach the systemic circulation, the patient develops carcinoid syndrome: episodic flushing, diarrhea, and wheezing. The symptoms are bizarre until you realize a tumor is broadcasting a hormone across the whole body.
Proving autonomy
The signature of a functional tumor is autonomy: it secretes regardless of feedback. So the way you prove it is to try to suppress it and watch it refuse. A normal cortisol axis shuts off when you give dexamethasone; a cortisol-secreting tumor keeps going. You confirm the syndrome biochemically first, then go looking with imaging — never the reverse, because incidental lumps are common and would mislead you.
Functional vs non-functional — how they show up
secretes? how found danger from
prolactinoma yes galactorrhea, low fertility hormone
pheochromocytoma yes BP spikes, headache, sweats hormone (crisis)
GH adenoma yes acromegaly (slow body change) hormone
carcinoid (NET) yes flushing, diarrhea, wheeze hormone
non-functional
adenoma no mass effect OR found by chance size
Diagnostic order: CONFIRM excess biochemically -> THEN image to localize
(functional tumors fail SUPPRESSION tests = they ignore feedback)