Neural transformation in a pituitary corticotroph adenoma.

A pituitary mass was removed by the transsphenoidal approach from a 63-year-old man with the clinical history and laboratory findings characteristic of Cushing's disease with partial hypopituitarism. Histological, immunohistochemical, ultrastructural and immunoelectron microscopic investigation demonstrated a periodic acid-Schiff-positive, adrenocorticotropic hormone (ACTH)-immunoreactive, pituitary corticotroph adenoma with the formation of neural tissue resembling neuropil within the tumor. The neural elements showed immunopositivity for neurofilament protein and ACTH, but were immunonegative for other adenohypophysial hormones and for corticotropin-releasing hormone. Although the molecular mechanism accounting for neural transformation in this corticotroph adenoma remained obscure, based on the clinical, histological and morphological findings it appears that formation of neural tissue most likely indicate a favorable prognosis.