A NULL-CELL ADENOMA OF THE PITUITARY DETECTED 7 YEARS AFTER REMOVAL OF A PROLACTINOMA - RECURRENCE OR DENOVO TUMORIGENESIS

We report an extremely unusual case of prolactinoma which emerged at r ecurrence as a null cell adenoma. A 53-year-old woman sought medical a ttention for progressive visual loss and headache. A pituitary tumour was detected by a computed tomographic scan, and hyperprolactinemia wa s noted. The tumour, removed by a transfrontal surgery, was a chromoph obe adenoma, and immunohistochemically the adenoma cells were selectiv ely positive for PRL, which indicated a prolactinoma. Postoperatively, her plasma PRL level was normalized. Seven years later, she noted blu rred 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 ante rior pituitary hormone including PRL, which indicated a null cell aden oma. We have no clear explanation of the pathogenesis underlying her v ery unusual course. However, null cells (assuming that the original tu mour was a mixed adenoma) left behind at the first surgery, or unident ified hypothalamic and/or pituitary derangements might possibly have b een responsible for the recurrence. We learned from this patient that recurrent pituitary adenomas may not necessarily have the same endocri ne features as did the original tumours. This information appears to m ake a valid clinical point, because if hormone levels alone are follow ed after pituitary surgery, recurrent pituitary tumours may be overloo ked.