The authors describe the case of a 36-year-old man who presented with
bitemporal hemianopsia and a serum
prolactin concentration of 1440 ng/ml. Magnetic 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 necessitated transsphenoidal resection, which was incomplete. Immunocytochemical analysis of the biopsy tissue was positive for
prolactin and, in view of the clinical picture, more detailed analysis was not performed. External-beam
radiotherapy was given 2 years later because of enlargement of
residual tumor. Subsequently, despite a fall in the serum
prolactin concentration 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 transfrontal
craniotomy for sudden deterioration in visual acuity caused by
hemorrhage into the mass. No adenohypophyseal tissue was identified in the resected tissue. The mass was composed of dysplastic neurons that were strongly immunoreactive for
synaptophysin and neurofilament (indicating neural differentiation) and
prolactin. Review of the original biopsy specimen indicated that the
prolactin-positive cells had striking neuronal morphological characteristics. The final diagnosis in this case is
prolactin-secreting
gangliocytoma. Although exceedingly rare, this disease must be added to the differential diagnosis in cases of "
prolactinoma" when
bromocriptine therapy is followed by a marked decline in serum
prolactin that is not accompanied by significant
tumor shrinkage. Furthermore, in such instances, consideration should be given to "obtaining a biopsy sample prior to electing for
radiotherapy.