A null cell adenoma of the pituitary detected seven years after removal of a prolactinoma. Recurrence or de novo tumourigenesis

: We report an extremely unusual case of prolactinoma which emerged at recurrence as a null cell adenoma. A 53-year-old woman sought medical attention for progressive visual loss and headache. A pituitary tumour was detected by a computed tomographic scan, and hyperprolactinemia was noted. The tumour, removed by a transfrontal surgery, was a chromophobe adenoma, and immunohistochemically the adenoma cells were selectively positive for PRL, which indicated a prolactinoma. Postoperatively, her plasma PRL level was normalized. Seven years later, she noted blurred vision and again sought medical attention. A CT scan demonstrated recurrence of a pituitary tumour. On this occasion, however, she was not hyperprolactinemic. She underwent again a transfrontal resection of the pituitary tumour. Its histology was again a chromophobe adenoma, but the adenoma cells showed no positive immunostaining for any anterior pituitary hormone including PRL, which indicated a null cell adenoma. We have no clear explanation of the pathogenesis underlying her very unusual course. However, null cells (assuming that the original tumour was a mixed adenoma) left behind at the first surgery, or unidentified hypothalamic and/or pituitary derangements might possibly have been responsible for the recurrence. We learned from this patient that recurrent pituitary adenomas may not necessarily have the same endocrine features as did the original tumours. This information appears to make a valid clinical point, because if hormone levels alone are followed after pituitary surgery, recurrent pituitary tumours may be overlooked.