The majority of
pituitary adenomas are solitary and monohormonal, producing only one
hormone. Double or multiple
adenomas are rare. Plurihormonal
adenomas may be monomorphous consisting of one cell type producing more than one
hormones or plurimorphous composed of two or more distinct cell populations each producing different
hormones. Primary pituitary
hyperplasia is uncommon and transformation to
adenoma has rarely been documented. We describe a unique case of
somatotroph adenoma combined with
ACTH-immunoreactive cell
hyperplasia and focal transformation to
adenoma. The 53-yr-old man was presented with a 2-yr history of
headaches, enlargement of the hands and feet and coarsening of facial features. His blood GH was 17.5 ng/ml and he had absence of GH suppressional oral
glucose tolerance testing. MRI demonstrated a mass with maximum diameter of 1.5 cm, on the left side of the pituitary, without invasion of surrounding tissues. Transsphenoidal surgery was performed. Morphology disclosed a mostly chromophobic
tumor, immunoreactive for GH with ultrastructural characteristics of sparsely granulated
somatotroph adenoma. The
adenoma cell population was focally admixed with hyperplastic PAS positive and
ACTH immunoreactive cells showing the electron microscopic features characteristic of corticotrophs. In these areas the acini were enlarged with distorted architecture of the
reticulin pattern. Dissolution of the
reticulin fiber network and transformation of hyperplastic
ACTH-immunoreactive cells to
adenoma was evident in small areas. The hyperplastic and adenomatous
ACTH-immunoreactive cells were admixed with
somatotroph adenoma cells. Due to lack of biochemically obvious
cortisol hypersecretion, this
ACTH-immunoreactive
adenoma was classified as silent "corticotroph" subtype 1. This is an unusual case of composite
pituitary adenoma consisting of somatotroph cells and hyperplastic
ACTH-immunoreactive cells transforming to a frank
adenoma.