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Pituitary Adenoma

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Overview

Pituitary tumours are the third most common adult brain tumour and are almost always benign and curable. They cause problems through excessive hormone production, the mass effect of the tumour itself, or inadequate hormone production from the rest of the pituitary gland. 

Classification

Non-functional vs. functional

Pituitary adenomas can be functional or non-functional depending on whether they secrete hormones in excess or not:

  • Non-functional – do not secrete a hormone in excess and are most common
  • Functional – secrete a hormone in excess – from most common to least common:
    • Prolactinomas – secrete excess prolactin
    • Somatotroph adenomas – secrete excess growth hormone (GH)
    • Corticotroph adenomas – secrete excess adrenocorticotropic hormone (ACTH)
    • Thyrotroph adenomas – secrete excess thyroid-stimulating hormone (TSH)
    • Gonadotroph adenomas – secrete excess follicle-stimulating hormone (FSH) and luteinising hormone (LH)

According to size

Pituitary adenomas can also be classified according to size:

  • Macroadenoma: tumour >1cm
  • Microadenoma: tumour <1cm

Epidemiology

  • Third most common brain tumour in adults
  • Adenomas make up most pituitary tumours, a minority of which are symptomatic
  • Prolactinomas are the most common functional pituitary adenoma
  • Many pituitary tumours are diagnosed incidentally

Risk Factors

Presentation

Pituitary adenomas cause symptoms by:

  • Excess production of a hormone:
  • Mass effect of the tumour itself:
    • Headaches – usually progressive and worse on waking/change with posture
      • Visual field defects:
        • Usually bitemporal hemianopia due to the tumour pressing on the optic chiasm, the upper half is affected more than the lower
      • Squint
      • Other features of Elevated Intracranial Pressure
  • Inadequate hormone production from the rest of the pituitary gland:
    • Compression on the rest of the pituitary gland can cause hypopituitarism
      • Non-functioning tumours may cause generalised hypopituitarism (panhypopituitarism) for this reason

Differential Diagnoses

Prolactin-secreting adenoma (prolactinoma)

  • Excess prolactin exerts negative feedback on gonadotropin-releasing hormone (GnRH):
  • In men: galactorrhoea, impotence, loss of libido
  • In women: galactorrhoea, amenorrhoea, infertility
  • Prolactin levels raised

Growth-hormone secreting adenoma (acromegaly)

  • Coarse facial features, increased shoe size, prognathism, excess sweating
  • Glucose intolerance present
  • Serum insulin-like growth factor 1 (IGF-1) raised

ACTH-secreting adenoma (Cushing’s disease)

  • Features of Cushing’s syndrome: central obesity, muscle wasting, bruising etc.
  • Impaired glucose tolerance and hypokalaemic metabolic alkalosis may be seen
  • Cortisol release is not suppressed with low-dose dexamethasone but is with high-dose

Thyroid-stimulating hormone-secreting adenoma

Non-functioning pituitary adenoma

  • Mass effect-related problems predominate: headaches, visual field defects
  • Panhypopituitarism may be present
  • Bitemporal hemianopia usually worse in upper half of visual field

Craniopharyngioma

  • More common in children and adults >60 years
  • Patients may have cranial diabetes insipidus
  • Bitemporal hemianopia usually worse in lower half of visual field

Investigations

  • Pituitary function tests:
    • Prolactin
    • IGF-1
    • FSH and LH
    • Oestrogen and testosterone
    • TFTs
    • ACTH
    • Morning cortisol
  • Urea and electrolytes (U&Es):
    • May show electrolyte disturbances
  • Pituitary MRI:
    • Shows pituitary mass
  • Visual field testing:
    • If imaging shows pressure on the optic chiasm

Management

Prolactin-secreting adenoma (prolactinoma)

  • 1st-line: dopamine agonists (cabergoline/bromocriptine)
  • If medical therapy ineffective/not tolerated: transsphenoidal surgery

Growth-hormone secreting adenoma (acromegaly)

  • 1st-line: transsphenoidal surgery
  • If surgery not possible/unsuccessful:
    • 1st-line: somatostatin analogue (octreotide)
    • 2nd-line: growth-hormone receptor antagonist (pegvisomant)
    • Consider dopamine agonist (cabergoline)
    • Consider radiotherapy

ACTH-secreting adenoma (Cushing’s disease)

  • 1st-line: transsphenoidal surgery

Thyroid-stimulating hormone-secreting adenoma

  • 1st-line: transsphenoidal surgery

Non-functioning pituitary adenoma

  • If microadenoma: observation
  • If macroadenoma with no mass effect: observation
  • If macroadenoma with mass effect: consider transsphenoidal surgery

Complications

Prognosis

  • Remission is often achieved in most patients with microadenomas and around half of those with macroadenomas
  • Most pituitary adenomas are benign and curable

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