Mr DP was referred by palliative care to ophthalmology with anisocoria, diplopia and nystagmus. He was known to have a poorly differentiated carcinoma of the prostate with skeletal metastasis (Gleason score 4+5=9). He was on hormonal therapy and had received radiotherapy to the cervical spine. PSA was normal, at 5.31 μg/l.
An MRI scan revealed a 12 mm mass in the left side of the pituitary gland, displacing the stalk to the right and lying close to the inferior surface of the optic chiasm. Prolactin was elevated at 897 μg/l in keeping with stalk compression, IGF1 was normal at 24 μg/l and cortisol peaked at 626 nmol/l on a short synacthen test. A repeat MRI 3 months later showed the tumour had grown to 15.5 mm, and was extending into the cistern touching the chiasm from below. Although a non-functioning pituitary adenoma was more probable in this location, the rate of growth was suggestive of possible metastasis.
Image guided endoscopic trans-sphenoidal resection of the tumour was arranged, and histological examination confirmed a moderately differentiated adenocarcinoma consistent with a metastatic deposit of the prostate. There were no postoperative visual complications. Follow up imaging at 3 months showed tumour residue reduced to 7 mm. Postoperative radiotherapy was not initiated as the patient became too unwell due to disseminated malignancy.
Prostate cancer is usually associated with lymph node, hepatic, skeletal and pulmonary metastases. Intracranial metastases are uncommon, with involvement of the pituitary gland rarer still. Small cell carcinoma of the prostate has a greater predilection to distant metastasis but this case represents a typical adenocarcinoma. Although unusual this case highlights the need to consider prostate metastasis to the pituitary, even with a normal PSA, as a metastatic deposit would potentially be more aggressive than a concurrent pituitary adenoma and would warrant earlier intervention.