A pituitary adenoma is a benign tumour of the pituitary gland. They are common (10% of all people) but in most cases will never be found (asymptomatic) or are found as an incidental finding. They account for around 10% of adult brain tumours.

Pituitary adenomas can be classified according to:

• size (a microadenoma is <1cm and a macroadenoma is >1cm)
• hormonal status (a secretory/functioning adenoma produces and excess of a particular hormone and a non-secretory/functioning adenoma does not produce a hormone to excess)

Prolactinomas are the most common type and they produce an excess of prolactin. After prolactinomas, non-secreting adenomas are the next most common, then GH secreting and then ACTH secreting adenomas.

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Pituitary adenomas typically cause symptoms by:

• excess of a hormone (e.g. Cushing’s disease due to excess ACTH, acromegaly due to excess GH or amenorrhea and galactorrhea due to excess prolactin)
• depletion of a hormone(s) (due to compression of the normal functioning pituitary gland)
  • non-functioning tumours, therefore, present with generalised hypopituitarism

Local effects:

• stretching of the dura within/around pituitary fossa (causing headaches)
• compression of the optic chiasm (causing a bitemporal hemianopia due to crossing nasal fibers)

Investigation requires:

• a pituitary blood profile (including: GH, prolactin, ACTH, FH, LSH and TFTs)
• formal visual field testing
• MRI brain with contrast
  • pituitary adenomas, particularly microadenomas, can be an incidental finding on neuroimaging and therefore called a ‘pituitary incidentaloma’.

Differential diagnoses include: