Pars intermedia of the human pituitary revisited: Morphologic aspects and frequency of hyperplasia of POMC-peptide immunoreactive cells
The human pituitary has no distinct pars intermedia (PI). Instead, the proopiomelanocortin (POMC) producing, adrenocorticotropin (ACTH)- and β-endorphin-immunoreactive PI cells are incorporated within the pars anterior, thereby participating in the formation of the pars distalis. Two hundred fifty autopsy pituitaries (156 males, 94 females) have been studied by histology and immunohistochemistry to determine the frequency of clinically non-functioning ACTH- and β-endorphin immunoreactive (POMC) cell hyperplasia/adenoma probably attributable to PI-derived cells. Such hyperplasia occurred in 29% of men and 14% of women; 80% of the male and 77% of the female subjects were over 50 yr of age. In two of the women, POMC cell adenoma was present as well. Except for hypothyroidism, none of the cases with POMC cell hyperplasia had endocrine disorder. No obvious correlation was evident between POMC cell hyperplasia/adenoma and clinical presentation. Hyperplasia of PI-derived POMC cells may be suspected by virtue of differential intraglandular localization of these cells. Except for cases of glucocorticoid treatment, leading to Crooke’s hyalinization of ACTH cells, but not affecting PI cells, no conclusive separation of various POMC-producing subsets is possible at present. The PI-derived cells probably give rise to silent “corticotroph” adenoma subtype 1 and subtype 2.
Key WordsHuman pituitary pars intermedia POMC cells hyperplasia adenoma
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