Hypopituitarism and posterior pituitary disorders
- Lesion
When most of the pituitary is destroyed, the glands it controls fail. The back lobe's ADH can be too low (diabetes insipidus) or too high (SIADH).
What it is
Hypopituitarism appears when roughly three quarters of the anterior lobe is lost. Tumours, surgery and radiation are the commonest causes, but ischaemic necrosis after childbirth, an empty sella, cysts, infiltrative disease and genetic defects also do it. The posterior lobe only stores and releases ADH and oxytocin made in the hypothalamus; too little ADH causes diabetes insipidus and too much causes SIADH.
Step by step
- ADH is made in the supraoptic and paraventricular nuclei and carried down axons to the posterior lobe.
- Damage to this axis (trauma, surgery, tumour, infiltration) lowers ADH: central diabetes insipidus.
- Collecting ducts cannot concentrate urine: polyuria, thirst and, without water access, hypernatraemia.
- In SIADH, ADH is released without an osmotic or volume trigger (tumour, CNS disease, lung disease, drugs).
- Water is retained, sodium is diluted and the brain swells: confusion, seizures.
Causes of anterior pituitary failure
| Group | Examples | What the pathologist sees |
|---|---|---|
| Mass lesions | Non-functioning PitNET, craniopharyngioma, metastasis | The compressing lesion |
| Ischaemic necrosis | Sheehan syndrome, DIC, sickle cell disease, shock | Infarct, later a small fibrotic gland |
| Haemorrhage | Pituitary apoplexy | Haemorrhagic necrosis of a tumour |
| Iatrogenic | Surgery, radiation | Scar |
| Inflammatory and infiltrative | Lymphocytic hypophysitis (often peripartum), IgG4 disease, sarcoidosis, Langerhans cell histiocytosis, haemochromatosis | Lymphocytes, granulomas, histiocytes, iron |
| Cysts and empty sella | Rathke cleft cyst, primary empty sella | Thin rim of compressed gland |
| Genetic | PIT1 (POU1F1) or PROP1 mutations | Small gland, missing cell lines |
| Hypothalamic | Tumours, trauma, radiation | Loss of releasing hormones |
Clinical notes
- Typical order of loss: GH and gonadotropins first, then TSH and ACTH; ACTH loss is the dangerous one.
- Secondary adrenal insufficiency spares aldosterone, so hyperkalaemia is absent and there is no hyperpigmentation.
- Nephrogenic diabetes insipidus (kidney resistance) looks similar but does not respond to ADH.
Test yourself
Think of the answer, then tap the question to see it.
Why is the pituitary vulnerable to infarction after obstetric haemorrhage?
In pregnancy the anterior lobe nearly doubles in size without a matching increase in its low-pressure portal blood supply, so hypotension infarcts it.
How do you tell central from nephrogenic diabetes insipidus?
Central improves when ADH (desmopressin) is given because the kidney still responds; nephrogenic does not.
Which tumour is the classic source of ectopic ADH?
Small cell carcinoma of the lung.
Elsewhere in DurgiPedia
- The posterior pituitary: ADH and oxytocin
- Pituitary: adenohypophysis and neurohypophysis
- Infarction: red vs white, and what decides the damage
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Diabetes insipidus: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Syndrome of inappropriate antidiuretic hormone secretion: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Pituitary Adenoma (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.