Endocrine Abstracts

A 44-year-old woman presented to an emergency department with ear pain and worsening of longstanding headache. There was no history of menstrual disturbance, galactorrhoea, tiredness or weight gain and physical examination demonstrated only a left homonymous hemianopia. CT head scan revealed a brightly enhancing, enormous, lobulated mass arising from the pituitary fossa and causing obstructive hydrocephalus through compression of the fourth ventricle. Following collection of blood and administration of dexamethasone the patient was transferred urgently to a neurosurgical centre.

Whole-brain MRI showed the mass arising from the pituitary fossa, encroaching the orbital apices anteriorly, compressing the pons posteriorly, elevating the floors of the lateral and third ventricles superiorly and eroding inferiorly into the left temporal fossa. Serum prolactin was reported as 3567 mIU/l. Right fronto-temporal craniotomy was performed. Histologically the tumour was a chromophobe pituitary adenoma with prolactin and occasional GH immunostaining.

Post-operatively the patient was transferred back to the referring hospital. She was panhypopituitary, hyperphagic and paranoid. A review of the biochemical results from the blood taken prior to transfer to the neurosurgical centre revealed that her pre-operative serum prolactin, which was outside the assay range initially, had been reported as 1045320 mIU/l (without evidence of macroprolactin). Cortisol, thyroid and gonadal results were within appropriate normal limits. Cabergoline was commenced and increased to 1 mg daily. The serum prolactin fell over weeks into the normal range. Serial MRI scans show substantial resolution of the tumour. The patient remains on anterior pituitary replacement and a reduced dose of cabergoline but, apart from a persistent visual field defect, has made a good recovery.

This case provides a useful reminder of the risk of ‘hook effect’ interference in some prolactin assays. It is all the more extraordinary because the patient was eupituitary pre-operatively, despite the enormous tumour.