Pituitary Incidentaloma

A pituitary incidentaloma is a sellar or parasellar lesion found on imaging done for an unrelated reason. It is a microincidentaloma if under 10 mm and a macroincidentaloma if 10 mm or more.

Small pituitary lesions are found in roughly 10% of people on MRI, and most are clinically silent adenomas. Prevalence rises with imaging use.

Causes are non-functioning and functioning adenomas, Rathke cleft cysts, meningioma, craniopharyngioma, arachnoid cyst, hypophysitis, metastasis, aneurysm and an empty sella.

Microincidentalomas rarely enlarge. Macroincidentalomas enlarge more often, in roughly one in five over several years, and apoplexy is uncommon.

Pathophysiology.

Most lesions are benign monoclonal adenomas that never cause hormone excess. Growth is slow and compression of the optic chiasm or normal gland develops only in macrolesions.

• Usually asymptomatic. Ask about headache, visual change, galactorrhoea, menstrual disturbance, libido, and features of Cushing syndrome and acromegaly.
• Examine visual fields and look for hypopituitarism.

Red flags.

• Visual field defect or optic chiasm contact on imaging.
• Sudden severe headache with visual or ocular movement disturbance (apoplexy).
• Diabetes insipidus (suggests a non-adenoma cause).

• Dedicated pituitary MRI with contrast. Compare with earlier imaging.
• Hormones for all lesions: prolactin, IGF-1, morning cortisol, thyroid stimulating hormone with free thyroxine, and (if indicated) a 1 mg overnight dexamethasone test, with cortisol over 50 nmol/L (1.8 micrograms/dL) as unsuppressed.
• Macroincidentaloma: assess all anterior pituitary axes (LH, FSH, testosterone or oestradiol), serum sodium, and visual fields and acuity if the lesion touches the chiasm.
• Characterise cystic or atypical lesions with further imaging; biopsy is rarely needed.

Differential diagnosis.

• Non-functioning adenoma, prolactinoma and other functioning adenoma.
• Rathke cleft cyst, craniopharyngioma, meningioma and arachnoid cyst.
• Hypophysitis, metastasis, lymphoma and germinoma.
• Carotid aneurysm and normal pituitary hyperplasia (pregnancy, primary gonadal or thyroid failure).

• Treat any hormone excess found (cabergoline for prolactinoma, surgery for acromegaly or Cushing disease) and replace deficits (hydrocortisone first, 15 to 25 mg daily in two or three divided doses).
• Microincidentaloma without excess: repeat MRI at 12 months, then every 2 years if stable, stopping at 3 to 5 years. Repeat hormones only if symptoms arise.
• Macroincidentaloma: MRI at 6 months, then yearly for 3 years, then less often; hormone and visual field review at each early visit.
• Surgery for visual compromise, apoplexy with deficits, documented growth, hypopituitarism or hormone excess not controlled medically.

Special groups. Pregnancy: macroadenomas may enlarge; assess before conception and examine visual fields each trimester if a macrolesion is present.

Monitoring. MRI at the intervals given, with visual fields for macrolesions near the chiasm.

Referral and escalation. Pituitary multidisciplinary team for macrolesions, any hormone abnormality or visual involvement. Same day review for apoplexy.