A functioning composite 'corticotroph' pituitary adenoma with interspersed adrenocortical cells.

We report the third case of a composite corticotroph pituitary adenoma with interspersed adrenocortical cells. The 16-year-old male patient presented with findings of delayed growth and pubertal arrest. In contrast to the previous two cases, this patient's tumor showed evidence of function as demonstrated by an elevated urinary cortisol level. Imaging studies revealed a sellar mass that was excised transsphenoidally. Histologic examination revealed a composite tumor composed of distinct populations of large and small cells. The small cell population was PAS-positive and immunohistochemically positive for adrenocorticotrophic hormone. The large cell population had abundant vacuolated cytoplasm, was negative for PAS and adrenocorticotrophic hormone, and stained positively for a panel of markers found in steroid-producing adrenocortical cells. Both populations showed evidence of proliferation as manifest by the presence of MIB-1 positive cells. Ultrastructural examination confirmed the presence of distinct populations of large adrenocortical cells and small corticotrophs, with intercellular junctions between the 2 cell types. The intimate relationship between the 2 cell population and the activated appearance of the adrenocortical cells suggests the possibility of a paracrine relationship between the two cell types. The identification of 3 patients with sellar tumors demonstrating strikingly similar morphological and ultrastructural features, and all occurring in the second decade of life, suggests that this represents a distinct pathologic entity.