A 30 year old man presented with Cushing’s disease. He had a pituitary macroadenoma and underwent transsphenoidal resection, with complete remission. Five years later, recurrence of his pituitary tumour involving the right cavernous sinus was treated with gamma-knife irradiation. Two years later, he again required transsphenoidal surgery because of intrasellar tumour expansion. Hypercortisolism persisted and bilateral laparoscopic adrenalectomy was attempted. This was aborted intraoperatively because of bleeding complications, leaving the left adrenal gland in situ. After initial improvement, his ACTH and cortisol levels again progressively increased. MRI scanning now showed a persistent lesion in the pituitary fossa and cavernous sinus, plus two additional lesions in the posterior fossa. Debulking surgery of the sellar mass failed to control his disease, use of mitotane was complicated by liver toxicity, and a trial of cabergoline was unsuccesful. He was then commenced on temozolomide. He developed severe headache and ataxia after his second cycle of treatment. Imaging showed recent enlargement of the two posterior fossa lesions. Urgent surgery revealed hemorrhage into a cerebropontine angle tumour, and multiple small leptomeningeal tumour deposits. Histopathology confirmed that the posterior fossa tumour was of pituitary origin. The Ki-67 index was <1% and the tumour was weakly positive for O-6-Methylguanine-DNA Methyl Transferase (MGMT). Treatment is continuing with temozolomide and pasireotide.
Pituitary carcinomas are rare tumours defined by the presence of craniospinal or systemic metastases. Most are highly aggressive lesions. Response to treatment is often disappointing and the prognosis is usually poor. However, this case illustrates that metastatic spread can occur with “benign histology” and a long, indolent disease course. Similar case reports exist of CNS metastatic spread from a pituitary adenoma that has otherwise benign characteristics – raising questions about the definition of pituitary carcinoma. Temozolomide is a promising therapy and low MGMT expression may predict a favourable response.