Blood says what, imaging says where
Endocrine diagnosis usually runs in two steps. First, a hormone assay and dynamic tests prove that a hormone is too high or too low — the biochemical diagnosis. Only then does gland imaging go looking for the physical cause. The order matters: imaging answers “where,” but it cannot answer “what is this lump doing,” and chasing pictures before the blood work leads you astray.
Different glands suit different scans. Ultrasound is gentle and excellent for the thyroid, sitting just under the skin of the neck. The pituitary, cradled deep in the skull, needs MRI to reveal a small pituitary adenoma. The adrenal gland, tucked above each kidney, is best seen on CT. Sometimes a radioactive tracer is added so that only the tissue making a particular hormone lights up, turning an anatomical map into a functional one.
The incidentaloma problem
Modern scans are so sensitive that they routinely find small lumps no one was looking for. A lump discovered by accident, while imaging for some unrelated reason, is an incidentaloma. They are extremely common: a large fraction of older adults have a tiny adrenal nodule or a thyroid nodule that has never caused harm and never will. The danger is not the lump itself but the temptation to over-investigate and over-treat it.
The two questions for any endocrine lump are simple: is it making hormone, and is it dangerous? A functional tumor secretes hormone on its own and causes symptoms; a non-functional endocrine tumor is silent. To answer the first question you go back to blood and urine tests — for an adrenal lump, that means screening for cortisol, aldosterone, and the catecholamines of a pheochromocytoma before anyone touches it.