Pituitary Disorders

The pituitary is a pea-sized gland tucked into a bony pocket at the base of the brain, yet it orchestrates thyroid function, growth, reproduction, the stress response, lactation, and water balance. When it over-produces, under-produces, or is compressed by a tumour, the effects ripple across nearly every organ system. Understanding pituitary disorders means learning to read the body as a signalling network — where a headache plus loss of peripheral vision, or enlarging hands and a deepening voice, can point straight back to this tiny "master gland."

This page teaches the four disorders you will meet most often in exams and on the wards — acromegaly, prolactinoma, diabetes insipidus, and hypopituitarism — anchored in the anatomy and physiology that make them make sense.

Learning Objectives

• Describe the anatomy of the hypothalamic-pituitary unit and the hormones of the anterior and posterior pituitary.
• Recognise the clinical features, diagnostic workup, and management of acromegaly and prolactinoma.
• Distinguish central (cranial) diabetes insipidus from nephrogenic DI and from primary polydipsia, and interpret the water deprivation test.
• Outline the causes, sequence of hormone loss, and replacement therapy in hypopituitarism, including pituitary apoplexy as an emergency.
• Appreciate the historical development of pituitary surgery and why Harvey Cushing matters.

Quick Answer

The pituitary has two lobes. The anterior pituitary makes six hormones (GH, prolactin, ACTH, TSH, LH, FSH) under hypothalamic control; the posterior pituitary stores and releases ADH (vasopressin) and oxytocin made in the hypothalamus. Most pituitary disorders arise from adenomas that either over-secrete a hormone or destroy normal tissue by mass effect. Acromegaly is GH excess in adults; prolactinoma (the commonest functioning adenoma) causes galactorrhoea, amenorrhoea, and low libido; diabetes insipidus is ADH deficiency (central) or resistance (nephrogenic) producing large-volume dilute urine; hypopituitarism is partial or complete loss of anterior pituitary hormones. Diagnosis blends hormone assays with dynamic testing and pituitary MRI; treatment ranges from dopamine agonists and somatostatin analogues to transsphenoidal surgery and lifelong hormone replacement.

Where It Came From

For most of medical history the pituitary was a mystery. Galen thought it drained "phlegm" (pituita) from the brain into the nose — hence the name — and this humoral misconception survived for over a thousand years. The link between the gland and disease came slowly. In the late nineteenth century, Pierre Marie described patients with grotesquely enlarged hands, feet, and jaws and coined the term acromegaly (Greek akron, extremity; megas, large) in 1886, and pathologists soon noticed these patients had enlarged pituitaries.

The transformative figure was Harvey Cushing, the American neurosurgeon who, in the first decades of the twentieth century, essentially founded pituitary surgery. Working before antibiotics, before modern imaging, and before hormone assays, he developed the transsphenoidal approach — reaching the gland through the nose and sphenoid sinus rather than opening the skull — refining techniques pioneered by Schloffer and Hirsch in Europe. In 1912 he published The Pituitary Body and its Disorders, and in 1932 he described the syndrome of cortisol excess from a pituitary tumour that now bears his name, Cushing's disease. His meticulous case records and low operative mortality (remarkable for the era) turned the pituitary from an untouchable structure into an operable one.

The other half of the story is the posterior pituitary. In the 1950s Vincent du Vigneaud isolated and synthesised oxytocin and vasopressin, the first peptide hormones ever chemically synthesised, winning the 1955 Nobel Prize and explaining diabetes insipidus at a molecular level. The need driving all this work was simple and human: patients were going blind, becoming infertile, wasting away, or urinating themselves into dehydration, and no one could explain why until the pituitary's role as a hormonal relay station was understood.

The Master Gland: Anatomy and Physiology

The pituitary sits in the sella turcica, a saddle-shaped depression of the sphenoid bone, connected to the hypothalamus above by the pituitary stalk (infundibulum). Directly above lies the optic chiasm — which is why an expanding pituitary tumour classically compresses the crossing nasal fibres and produces bitemporal hemianopia (loss of the outer half of each visual field). On either side run the cavernous sinuses carrying the internal carotid arteries and cranial nerves III, IV, V1, V2, and VI.

Functionally, think of it as two glands:

• Anterior pituitary (adenohypophysis): glandular tissue controlled by releasing and inhibiting hormones delivered from the hypothalamus through the hypophyseal portal veins. It secretes growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), luteinising hormone (LH), and follicle-stimulating hormone (FSH).
• Posterior pituitary (neurohypophysis): not a gland but the axon terminals of hypothalamic neurons, storing antidiuretic hormone (ADH/vasopressin) and oxytocin.

A crucial exception governs prolactin: it is under tonic inhibition by dopamine from the hypothalamus. Cut the stalk (by a tumour or trauma), and prolactin rises while every other anterior hormone falls — the so-called "stalk effect." This single fact explains many exam scenarios.

Acromegaly: Growth Hormone Excess

Acromegaly is caused, in over 95% of cases, by a GH-secreting pituitary adenoma. GH drives the liver to produce insulin-like growth factor 1 (IGF-1), the true mediator of most effects. Before puberty, before the growth plates fuse, GH excess causes gigantism; after fusion, bones cannot lengthen but can thicken, producing the characteristic acromegalic phenotype.

Clinical features develop insidiously over years — patients often only realise when old photographs are compared:

• Coarsening facial features, enlarged nose and lips, prominent brow (frontal bossing), prognathism (protruding jaw with dental spacing).
• Enlarging hands and feet — the classic history is a wedding ring that no longer fits or a rising shoe size.
• Sweating, oily skin, deep husky voice, macroglossia (enlarged tongue causing obstructive sleep apnoea).
• Carpal tunnel syndrome, arthropathy, hypertension, cardiomyopathy, and impaired glucose tolerance or diabetes (GH is a counter-regulatory hormone).
• Colonic polyps and an increased colon cancer risk warranting colonoscopy screening.

Worked diagnostic example: A 48-year-old man reports headaches, sweating, and rings that no longer fit. Random GH is unreliable because it is pulsatile, so you measure IGF-1, which is elevated for his age. The confirmatory test is the oral glucose tolerance test (OGTT): give 75 g glucose and measure GH — in a healthy person glucose suppresses GH to below 1 microgram/L, but in acromegaly GH fails to suppress. Pituitary MRI then shows a macroadenoma. This sequence (screen with IGF-1, confirm with OGTT, localise with MRI) is a reliable exam answer.

Management: First-line is transsphenoidal surgery. If surgery is incomplete or the patient is not a candidate, medical therapy includes somatostatin analogues (octreotide, lanreotide), the GH-receptor antagonist pegvisomant, and dopamine agonists (cabergoline) in milder cases. Radiotherapy is reserved for resistant disease. Untreated acromegaly roughly doubles mortality, mainly cardiovascular — so it is not a cosmetic problem.

Prolactinoma and Diabetes Insipidus

Prolactinoma is the most common functioning pituitary adenoma. Excess prolactin suppresses GnRH, and therefore LH and FSH, causing hypogonadism. In women it produces amenorrhoea, galactorrhoea, and infertility and is often caught early (small microadenomas). In men it causes low libido, erectile dysfunction, and infertility and is usually caught late as a large macroadenoma with visual field loss.

A vital diagnostic caveat: not every high prolactin is a prolactinoma. The stalk effect (any large sellar mass) raises prolactin modestly (usually under ~2000 mU/L), whereas a true prolactinoma often drives it much higher. Always exclude physiological and drug causes first — pregnancy, hypothyroidism (high TRH stimulates prolactin), and dopamine-blocking drugs (antipsychotics, metoclopramide, some antidepressants). Uniquely among pituitary tumours, prolactinoma is treated medically first: dopamine agonists (cabergoline, bromocriptine) shrink the tumour and normalise prolactin in most patients, reserving surgery for drug-resistant or intolerant cases.

Diabetes insipidus (DI) has nothing to do with sugar — the name reflects the huge volumes of insipid (tasteless) dilute urine, in contrast to the sweet urine of diabetes mellitus. It results from a problem with ADH:

• Central (cranial) DI: the pituitary/hypothalamus fails to make or release ADH — from surgery, tumour, trauma, or autoimmune infiltration.
• Nephrogenic DI: the kidney fails to respond to ADH — from lithium therapy, hypercalcaemia, hypokalaemia, or genetic receptor defects.

Patients pass 3 or more litres of dilute urine daily with intense thirst (polydipsia). The key test is the water deprivation test followed by desmopressin:

Response after fluid deprivation, then desmopressin	Interpretation
Urine stays dilute, then concentrates after desmopressin	Central DI (kidney can respond once ADH is supplied)
Urine stays dilute, no response to desmopressin	Nephrogenic DI
Urine concentrates normally with deprivation alone	Primary polydipsia

Central DI is treated with desmopressin (DDAVP), a synthetic ADH analogue. Nephrogenic DI is managed by removing the cause, a low-salt/low-protein diet, and paradoxically thiazide diuretics.

Hypopituitarism and Pituitary Apoplexy

Hypopituitarism is the deficiency of one (partial) or all (panhypopituitarism) anterior pituitary hormones. Causes include large non-functioning adenomas, surgery, radiotherapy, Sheehan syndrome (postpartum pituitary infarction after major obstetric haemorrhage), traumatic brain injury, infiltrative disease (sarcoidosis, haemochromatosis), and autoimmune hypophysitis.

Hormones are typically lost in a characteristic sequence, remembered as "Go Look For The Adenoma" — GH first, then LH/FSH (gonadotropins), then TSH, and finally ACTH. This matters because GH and gonadotropin loss cause subtle chronic symptoms (fatigue, low libido, amenorrhoea), whereas ACTH loss producing secondary adrenal insufficiency can be life-threatening.

A critical clinical rule: replace cortisol before thyroxine. Giving levothyroxine to a cortisol-deficient patient accelerates cortisol metabolism and can precipitate an adrenal crisis. Replacement is otherwise straightforward in principle: hydrocortisone for ACTH deficiency, levothyroxine for TSH deficiency, sex steroids for gonadotropin deficiency, and recombinant GH in selected patients. Note that secondary adrenal insufficiency does not cause hyperpigmentation (ACTH is low, not high) or hyperkalaemia (aldosterone, driven by the renin-angiotensin system, is preserved) — a useful contrast with primary Addison's disease.

Pituitary apoplexy is the emergency: sudden haemorrhage or infarction of a pituitary tumour, presenting with thunderclap headache, visual loss, ophthalmoplegia, and acute hypopituitarism. It requires urgent stress-dose hydrocortisone, endocrine and neurosurgical input, and consideration of decompressive surgery.

Real-World Applications

• Primary care vigilance: Acromegaly is often missed for years. A GP who notices coarsening features, new diabetes plus carpal tunnel, or a jaw that no longer bites evenly can shorten years of undiagnosed cardiovascular damage.
• Medication review: New galactorrhoea or amenorrhoea in a patient on antipsychotics should prompt a prolactin check before an expensive MRI — drug-induced hyperprolactinaemia is common and reversible.
• Post-operative and ICU care: After pituitary surgery or head injury, meticulous fluid-balance charting catches central DI early; unrecognised, it causes rapid hypernatraemia and dehydration.
• Obstetrics: A mother who cannot breastfeed and has persistent fatigue after a haemorrhagic delivery may have Sheehan syndrome — a diagnosis that saves lives when acted on.

Common Mistakes

1. "Diabetes insipidus is a type of diabetes mellitus." Wrong — they share only the word "diabetes" (Greek for "to pass through," referring to polyuria). DI involves ADH and water balance; DM involves insulin and glucose. Correction: check osmolality and glucose — DI gives dilute urine with normal-to-high serum sodium and normal glucose.
2. "A raised prolactin always means a prolactinoma." Wrong — pregnancy, hypothyroidism, dopamine-blocking drugs, and the stalk effect of any sellar mass all raise prolactin. Correction: exclude physiological and drug causes and interpret the magnitude; very high levels favour a true prolactinoma.
3. "Treat every pituitary tumour with surgery first." Wrong for prolactinoma — dopamine agonists are first-line and shrink most of them without surgery. Correction: prolactinoma is the exception where medical therapy leads.
4. "Start thyroxine as soon as you find low TSH-driven thyroid function in hypopituitarism." Dangerous — always replace cortisol first to avoid precipitating adrenal crisis.

Comparison and Connections

Feature	Acromegaly	Prolactinoma	Central DI	Hypopituitarism
Core problem	GH/IGF-1 excess	Prolactin excess	ADH deficiency	Anterior hormone loss
Hallmark clue	Enlarging hands/jaw	Galactorrhoea, amenorrhoea	Large-volume dilute urine	Fatigue, hypogonadism
Key test	IGF-1, OGTT non-suppression	Serum prolactin	Water deprivation test	Basal hormones + dynamic tests
First-line treatment	Surgery	Dopamine agonist	Desmopressin	Hormone replacement

Contrast secondary (pituitary) adrenal insufficiency with primary (Addison's): primary disease has high ACTH (hyperpigmentation) and low aldosterone (hyperkalaemia, salt craving), while secondary has low ACTH and preserved aldosterone. Similarly distinguish SIADH (too much ADH, causing hyponatraemia and concentrated urine) from DI (too little ADH) — mirror images of water handling.

Practice Questions

Recall

Q: Which pituitary hormone is under predominantly inhibitory hypothalamic control? A: Prolactin, inhibited by dopamine — which is why stalk compression or dopamine-blocking drugs raise it.

Understanding

Q: Why does an expanding pituitary macroadenoma cause bitemporal hemianopia? A: The tumour grows upward and compresses the optic chiasm, damaging the crossing nasal retinal fibres that carry information from the temporal (outer) visual fields of both eyes.

Application

Q: A patient on lithium develops polyuria and polydipsia. Water deprivation fails to concentrate the urine, and there is no response to desmopressin. Diagnosis and management? A: Nephrogenic diabetes insipidus. Manage by reviewing/stopping lithium if possible, correcting any electrolyte disturbance, a low-solute diet, and thiazide diuretics.

Analysis

Q: A woman with a large pituitary mass has a prolactin of 1500 mU/L (mildly elevated). Is this a prolactinoma? Justify. A: Probably not a prolactinoma — the level is only modestly raised, more consistent with the stalk effect from a non-functioning macroadenoma disinhibiting prolactin. A true macroprolactinoma of that size would usually produce a much higher prolactin. This distinction changes management: a non-functioning tumour with visual compromise needs surgery, whereas a prolactinoma responds to dopamine agonists.

FAQ

Is acromegaly reversible? Soft-tissue changes (swelling, sweating, carpal tunnel) often improve substantially with treatment, but bony changes such as an enlarged jaw and enlarged hands are permanent. Early treatment prevents progression and reduces cardiovascular mortality.

Can prolactinomas affect men? Yes, but they present differently — low libido, erectile dysfunction, and infertility rather than galactorrhoea, so they are often diagnosed later and larger.

Why is cortisol replaced before thyroxine in hypopituitarism? Thyroxine speeds up metabolism, including the clearance of cortisol. In a patient already low on cortisol, this can tip them into an adrenal crisis. Cortisol first, then thyroxine.

How is central DI different from just drinking too much water? In primary polydipsia the kidneys can still concentrate urine during water deprivation because ADH works normally; in central DI they cannot until desmopressin is given. Serum sodium tends to be high-normal in DI and low-normal in primary polydipsia.

What is pituitary apoplexy and why is it urgent? It is sudden bleeding or infarction into a pituitary tumour causing severe headache, visual loss, and acute cortisol deficiency. Without prompt stress-dose steroids and specialist care it can be fatal.

Do all pituitary tumours secrete hormones? No. Many are non-functioning adenomas that cause problems purely by mass effect (visual loss, headache, hypopituitarism) rather than by hormone excess.

Quick Revision

• Anterior pituitary: GH, PRL, ACTH, TSH, LH, FSH. Posterior: ADH and oxytocin (made in hypothalamus).
• Prolactin is dopamine-inhibited; stalk damage raises prolactin, lowers everything else.
• Acromegaly: screen IGF-1, confirm with OGTT (GH fails to suppress), treat with surgery first.
• Prolactinoma: commonest functioning adenoma; dopamine agonists (cabergoline) are first-line.
• DI: dilute urine + thirst. Central responds to desmopressin; nephrogenic does not.
• Hypopituitarism hormone loss order: GH, gonadotropins, TSH, ACTH. Replace cortisol before thyroxine.
• Pituitary apoplexy = emergency: hydrocortisone + urgent specialist review.
• Bitemporal hemianopia = chiasmal compression by a sellar mass.

Related Topics

Prerequisites

• Endocrinology overview
• Physiology of hormonal control — see Physiology

Related Topics

• Adrenal disorders and Cushing's syndrome (within Endocrinology)
• Thyroid disorders (within Endocrinology)
• Fluid, electrolyte, and sodium balance — see Nephrology

Next Topics

• Adrenal Disorders
• Diabetes Mellitus and glucose regulation