Background: Prolactinomas are the major subtype (2030%) of pituitary adenomas. Microprolactinomas (<1 cm) are commoner in females, whereas macroprolactinomas (>1 cm) occur mainly in men. Giant prolactinomas are rare (23% of prolactinomas) features include size of ≥4 cm, with significant extrasellar extension and prolactin levels of >1000 μg/l.
Case report: We report the case of a 35-year-old man with type 2 diabetes, who presented following a generalised seizure. He gave a history of twice-weekly headaches and generalised fatigue, but denied visual disturbance, erectile dysfunction, or loss of libido. MRI showed a 3.2×3.5×4.8 cm intra- and suprasellar mass with cavernous sinus invasion causing significant mass effect on the right temporal lobe. Examination revealed sparse chest hair, bilateral testicular volume of 10 ml, normal genitalia and pubic hair. Visual field tests were normal. Total prolactin was 11 966 000 mU/l with bioactive monomeric prolactin of 128 520 mU/l. FSH was 12.1 IU/l, LH 6.1 IU/l, and testosterone 5.3 nmol/l. IGF1 was 19 nmol/l, GH <0.10 μg/l, TSH 2.57 mU/l, FT4 11 pmol/l, ACTH 7 ng/l, and 0900 h cortisol 574 nmol/l. He was commenced on cabergoline 250 μg twice-weekly and levetiracetam 250 mg twice daily, and referred to neurosurgery. Prolactin levels fell to 991 mU/l within 2 weeks, and continue to decline (271 mU/l at 8 months and 143 mU/l at 11 months). Repeat MRI at 4 months showed decrease in tumour size to 3×4.2 cm. The patient has had no further generalised seizures.
Conclusion: Pituitary macroadenomas usually cause complex partial seizures, and most patients have epilepsy prior to diagnosis of a macroadenoma. Uniquely, this patient first presented with a generalised seizure, and visual fields were spared despite cavernous sinus invasion. It also illustrates the importance of checking prolactin when an intracranial mass is found on neuroimaging, to avoid unnecessary neurosurgical intervention. Excellent biochemical response and decrease in tumour size support the view that cabergoline is an effective first-line treatment for giant prolactinomas.