Pituitary Pathology
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Direct answer
Pituitary pathology centres on adenomas, classified by size (micro below 10 mm, macro above) and secretion — prolactinoma the commonest functioning type, then growth hormone and ACTH tumours causing acromegaly and Cushing disease. Non-functioning macroadenomas and craniopharyngiomas cause mass effects with bitemporal hemianopia, while apoplexy and Sheehan syndrome are the acute and postpartum failure states. Posterior pituitary disease is diabetes insipidus and the syndrome of inappropriate ADH with hyponatraemia.
What you must remember
- Prolactinoma: women present with amenorrhoea, galactorrhoea and infertility, men with erectile dysfunction or visual loss from a macroadenoma; antipsychotics raise prolactin by dopamine blockade; dopamine agonists (cabergoline, bromocriptine) are first-line.
- Acromegaly: growth hormone excess after epiphyseal closure — large hands and feet, jaw prognathism, macroglossia, hypertension, diabetes and cardiomyopathy with colon polyp risk; screen with IGF-1, confirm by failure of growth hormone to suppress during a glucose load; transsphenoidal surgery, with somatostatin analogues or pegvisomant as adjuncts. Before closure the same excess causes gigantism.
- Cushing disease: ACTH-secreting pituitary microadenoma driving bilateral adrenal hyperplasia; confirmed by high-dose dexamethasone suppression and inferior petrosal sinus sampling within the wider workup.
- Mass effects: bitemporal hemianopia from chiasmal compression; stalk compression mildly raises prolactin (stalk effect) and must not be mistaken for a prolactinoma.
- Emergencies and failure: apoplexy — haemorrhage into an adenoma with thunderclap headache, ophthalmoplegia and hypopituitarism needing corticosteroids and surgery; Sheehan syndrome — postpartum necrosis with failure of lactation the earliest sign; craniopharyngioma — calcified suprasellar Rathke-remnant tumour of children compressing chiasm and hypothalamus.
- Diabetes insipidus: central (trauma, surgery, craniopharyngioma) responds to desmopressin; nephrogenic (lithium, hypercalcaemia) does not; water deprivation testing with desmopressin response separates them.
- SIADH: small cell lung cancer, CNS disease and drugs such as carbamazepine; euvolaemic hyponatraemia with urine osmolality above 100 and urinary sodium above 40, treated by fluid restriction, hypertonic saline for seizures.
Common confusion
Craniopharyngioma versus pituitary adenoma: calcified suprasellar childhood tumour against the adult sellar mass, both giving bitemporal field loss. Central versus nephrogenic diabetes insipidus is settled by urine concentration after desmopressin. In Cushing medicine, pituitary disease suppresses with high-dose dexamethasone while ectopic ACTH does not — and exogenous steroids remain the commonest cause overall.
Exam-focused takeaway
FMGE gives a hormone excess and asks for the tumour and first-line drug, or a visual field and asks for the site. Prolactinoma-cabergoline, acromegaly-IGF-1 with failed suppression, Sheehan failure of lactation, apoplexy steroids and the SIADH pattern of euvolaemic hyponatraemia with concentrated urine are the recurring marks.
Frequently asked questions
Which pituitary tumour is most common?
Non-functioning adenoma overall; prolactinoma among secreting types, declared by amenorrhoea-galactorrhoea in women or visual loss from a macroadenoma.
How is acromegaly diagnosed?
Elevated IGF-1 screening, then failure of growth hormone to suppress during an oral glucose tolerance test; imaging localises the adenoma for transsphenoidal surgery.
What is Sheehan syndrome?
Postpartum ischaemic pituitary necrosis after severe haemorrhage, beginning with failed lactation and progressing to panhypopituitarism; each axis needs replacement.
How are the two diabetes insipidus types separated?
After water deprivation, desmopressin concentrates urine in central disease but not in nephrogenic resistance; plasma ADH levels confirm where available.
Which malignancy most often causes SIADH?
Small cell lung carcinoma through ectopic ADH; CNS disorders and drugs such as carbamazepine follow. Correct sodium gradually to avoid osmotic demyelination.
What is pituitary apoplexy?
Acute haemorrhage into an adenoma causing sudden headache, ocular palsy, visual loss and adrenal insufficiency; urgent hydrocortisone with neurosurgical assessment.