A 75-year-old man was admitted acutely with a 1 week history of headaches, reduced visual acuity, diplopia and ptosis of his left eye. Examination confirmed a left III and VI nerve palsies with decreased visual acuity in the left eye. A CT and subsequent MRI revealed pituitary mass lesion measuring 2.4×2.1×1.5 cm with extension into the left cavernous sinus. The pituitary stalk appeared thickened and was deviated to the right. The optic apparatus was uninvolved.
He had a background history of adenocarcinoma of the ascending colon with right hemicolectomy in March 2007 and in July 2009 he had undergone a left upper lobe metastectomy for a lung metastasis. A repeat CT of his chest and abdomen revealed a left upper lobe mass with enlarged mediastinal lymph nodes.
His pituitary hormone profile showed a markedly elevated prolactin and anterior pituitary failure: prolactin 8766 mU/l (50700), LH 0.6 U/l (1.09.0), FSH 2.0 U/l (1.010.0), testosterone <0.4 nmol/l (8.027.0), IGF1 8.0 nmol/l (7.022.0), cortisol 68 nmol/l (184623), TSH 0.08 mU/l (0.24.0) and T4 7.9 pmol/l (8.021.0). Macroprolactin was excluded. He was commenced on cabergoline 500 μg once daily, hydrocortisone and levothyroxine. His prolactin corrected rapidly, falling to 83 mU/l after two weeks. However a repeat MRI showed no change in the size of the pituitary mass. Subsequently he underwent transsphenoidal surgery to debulk his pituitary mass and confirm the aetiology. Histology showed moderately differentiated adenocarcinoma compatible with a metastasis from gut primary. Immunohistochemistry showed no evidence of prolactin secretion from within the tumour. He deteriorated quickly and died four months later.
This case demonstrates an unusually high prolactin level which is not due to a prolactinoma but instead is due to stalk disconnection hyperprolactinaemia from a rare occurrence of a pituitary metastasis.