Some clinically silent tumors are recognized by electron microscopy as having gonadotropic differentiation, but some have characteristics of less well differentiated cells, resembling the "null" cells that were initially thought to be undifferentiated precursors of adenohypophysial cells.
Hyperplasia of adenohypophysial cells can give rise to clinical syndromes and even radiologic features that are indistinguishable from pituitary adenomas.
Adenohypophysial hyperplasia can be distinguished from adenoma histologically with a reticulin stain.