Ganglion cell containing pituitary adenomas: signs of neuronal differentiation in adenoma cells

Ganglion cell containing pituitary adenomas are rare. They represent tumors originating in the sella turcica which are composed of adenomatous and neuronal components. Recently accumulated information suggests a common origin for their neuronal and pituitary constituents. The objective of this study was to report the clinical and morphologic findings of pituitary gangliocytomas and study their immunoprofile using neuronal markers. Seven cases of pituitary gangliocytomas retrieved from 1,322 sellar lesions were studied. All tumors were removed from patients with mild acromegaly. Histologically they were biphasic composed of pituitary adenoma and clusters of ganglion cells embedded in a variably dense neuropil substrate. All adenomas belonged to the category of sparsely granulated somatotroph adenoma and were positive for growth hormone, whereas in five tumors, a few adenoma cells were also positive for prolactin. Ganglion cells were immunoreactive for NSE, synaptophysin and neurofilament protein (NFP). NFP-reactive fibrils were observed in the neuropil substrate and varied in number among the cases. Interestingly, all tumors contained varying numbers of adenoma cells with NFP-positive, dot-like areas of cytoplasmic reactivity, mostly tiny paranuclear, a finding not previously reported in human pituitary gangliocytomas. The presence of NFP in pituitary adenomas indicates neuronal differentiation in adenoma cells, suggesting a common origin for neuronal and pituitary adenoma cell elements in gangliocytomas.