Proliferation of adenohypophyseal cells into posterior lobe. Their normal anatomical condition and possible neoplastic potentiality.

Proliferation of pituitary basophil cells and occasional chromophobe and eosinophil cells into the posterior lobe was found in 61.8 +/- 6.9% (alpha = 0.05) in routine necropsy series. The incidence and intensity of proliferation increased in accordance with increasing age. There were no sex differences. The cells were for the most part ACTH-productive; only a few were found to produce somatotropic hormone (STH) or prolactin in exceptional cases, when examined immunocytochemically. Proliferation of these cells appears to take place postnatally, probably in young adult ages. Basophil proliferation, stemming from the pars intermedia, was not related to any clinical features. However, in 6 out of 191 examined cases (3.1 +/- 2.5%), the proliferating cells displayed neoplastic potentiality, demonstrated as a combination of mitoses, multinuclear cells, polymorphism, and hypertrophy of the protoplasma in addition to intense proliferation. This finding, described for the first time, may contribute to a better understanding of the origin of silent corticotrophic cell adenomas.