Background: Pituitary carcinoma is extremely rare and constitute only 0.1−0.2% of all pituitary tumors. Diagnosis is on evidence of metastasis, although these criteria has been challenged. Majority of pituitary carcinomas are functioning tumours, usually secreting ACTH (42%) or prolactin (33%). Common sites of metastasis include the brain, spinal cord, leptomeninges, bone, liver, lymph nodes and lung. Mean survival after detection of metastasis is around 1−2 years.
Case history: A 68 year-old-lady, known to have resistant macroprolactinoma for 10 years, but not seen over the last year, presented with a progressively enlarging 3 cm occipital scalp lump over 6 months duration. In the past she refused surgery, therefore she was treated with cabergoline 7 mg/week and pituitary radiotherapy in 2014. Her prolactin was 851 mIU/l post-radiotherapy and one year later it has risen to 123 340 mIU/l without significant change in her pituitary lesion. CT showed an erosive soft tissue mass arising from the dura and encompassing the full thickness of the bone and the scalp lesion. Biopsy revealed pituitary tissue with positive prolactin staining and a high Ki-67 (27%) with p53 positivity confirming the diagnosis of pituitary carcinoma. Retrospective analysis of MRI scans of the preceding 2 years revealed the emergence of a small occipital dural metastasis, which was not noted by the radiological reports. Bone scan revealed multiple vertebral and bone metastasis. Patient received temozolmide and radiotherapy to three areas with metastatic lesions. She had a marked clinical (lesion size <1 cm) and biochemical (prolactin 2024 mIU/l) response over next 12 months. She died 2 years after the diagnosis of the metastasis.
Conclusion: Pituitary carcinomas can have rare clinical presentation with dural metastasis causing a large lesion in the skull. Significant increase in prolactin levels without change in size of an invasive macroprolactinoma may raise the suspicion of metastasis. Early diagnosis of metastasis could lead to initiation of temozolamide and radiotherapy.