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 findings. 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 an 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.

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

Alternatively, pituitary adenomas, particularly microadenomas, can be an incidental finding on neuroimaging and therefore called a 'pituitary incidentaloma'.

Investigation requires:

• a pituitary blood profile (including GH, prolactin, ACTH, FSH, LSH and TFTs)
• formal visual field testing
• MRI brain with contrast

Differential diagnoses include:

• pituitary hyperplasia
• craniopharyngioma
• meningioma
• brain metastases