Gangliocytoma masquerading as a prolactinoma - Case report

The authors describe the case of a 36-year-old man who presented with bitem poral hemianopsia and a serum prolactin concentration of 1440 ng/ml. Magnet ic resonance imaging of the pituitary revealed a presumed macroadenoma with suprasellar and temporal lobe extension. Although the patient's prolactin level was lowered to 55 ng/ml by bromocriptine therapy, no tumor shrinkage occurred. Fourteen months later, progression of visual field defects necess itated transsphenoidal resection, which was incomplete. Immunocytochemical analysis of the biopsy tissue was positive for prolactin and, in view of th e clinical picture, more detailed analysis was not performed. External-beam radiotherapy was given 2 years later because of enlargement o f residual tumor. Subsequently, despite a fall in the serum prolactin conce ntration to less than 20 ng/ml in response to the course of bromocriptine, the mass displayed further extension into the temporal lobe. Nine years after the patient's initial presentation, he underwent transfron tal craniotomy for sudden deterioration in visual acuity caused by hemorrha ge into the mass. No adenohypophyseal tissue was identified in the resected tissue. The mass was composed of dysplastic neurons that were strongly imm unoreactive for synaptophysin and neurofilament (indicating neural differen tiation) and prolactin. Review of the original biopsy specimen indicated th at the prolactin-positive cells had striking neuronal morphological charact eristics. The final diagnosis in this case is prolactin-secreting gangliocy toma. Although exceedingly rare, this disease must be added to the differen tial diagnosis in cases of "prolactinoma" when bromocriptine therapy is fol lowed by a marked decline in serum prolactin that is not accompanied by sig nificant tumor shrinkage. Furthermore, in such instances, consideration sho uld be given to obtaining a biopsy sample prior to electing for radiotherap y.