Morphologically unclassified GH-producing adenoma showing galactorrhea without acromegaly

A 24-year-old woman with a large pituitary adenoma had amenorrhea and galactorrhea, but no physical stigmata of acromegaly despite slightly elevated serum growth hormone (GH) and normal serum prolactin (PRL) levels. Subtotal removal of the tumor cured galactorrhea and resulted in normalization of serum GH concentration. The question is raised whether amenorrhea and galactorrhea were related to excessive GH production in this patient. Absence of acromegaly might have been due to the short duration of the disease. The tumor was a chromophobic, periodic acid-Schiff-negative adenoma. Immunocytochemistry and in situ hybridization revealed focal GH immunoreactivity and diffuse, weak signal for GH messenger RNA. By electron microscopy, the tumor showed no features of GH or PRL-producing adenomas. Two different cell types could be distinguished: the majority were similar to null cells, whereas a small number of cells resembled somatotrophs and lactotrophs, possessing many secretory granules and exhibiting exocytosis. On the basis of its ultrastructure, this tumor can be classified as an atypical acidophil cell line adenoma in which adenomatous null cells transformed to the differentiated cells capable of producing GH.