An excess of
growth hormone (GH) results in accelerated growth and in childhood, the clinical manifestation is
gigantism. When GH excess has its onset after epiphyseal fusion at puberty, the overgrowth of soft tissue and bone results in
acromegaly. Persistent GH excess in
gigantism also causes acromegalic features that become evident in the adult years. The causes of GH excess are primarily lesions in the pituitary, which is the main source of GH. In this review, we provide an update on the clinical, radiological and pathologic features of the various types of pituitary
neuroendocrine tumors (PitNETs) that produce GH. These
tumors are all derived from PIT1-lineage cells. Those composed of somatotrophs may be densely granulated, resembling normal somatotrophs, or sparsely granulated with unusual fibrous bodies. Those composed of mammosomatotrophs also produce
prolactin; rare plurihormonal
tumors composed of cells that resemble mammosomatotrophs also produce TSH. Some PitNETs are composed of immature PIT1-lineage cells that do not resemble differentiated somatotrophs, mammosomatotrophs, lactotroph or thyrotrophs; these
tumors may cause GH excess. An unusual oncocytic PIT1-lineage
tumor known as the acidophil stem cell tumor is predominantly a lactotroph
tumor but may express GH. Immature PIT1-lineage cells that express variable amounts of
hormones alone or in combination can sometimes cause GH excess. Unusual
tumors that do not follow normal lineage differentiation may also secrete GH. Exceptional examples of
acromegaly/
gigantism are caused by sellar
tumors composed of hypothalamic GHRH-producing neurons, alone or associated with a sparsely granulated somatotroph
tumor. Each of these various
tumors has distinct clinical, biochemical and radiological features. Data from careful studies based on morphologic subtyping indicate that morphologic classification has both prognostic and predictive value.