Pituitary adenoma classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Pituitary adenomas are tumors that occur in the pituitary gland, and account for about 10% of intracranial neoplasms. They often remain undiagnosed, and small pituitary tumors are found in 6 to 24 percent of adults at autopsy. Pituitary adenomas arise within the anterior lobe (adenohypophysis) of the gland . Tumors less than 1 cm are called micro adenomas. Clinical symptoms depend on whether the tumor is secreting or nonsecreting. Nonsecreting adenomas grow and compress adjacent structures, most commonly causing a bitemporal hemianopsia due to chiasmatic compression. Lateral extension into the cavernous sinuses can result in cranial nerve palsies.

Classification

Pituitary tumors were, historically, classed as basophilic, acidophilic, or chromophobic on the basis of whether or not they took up the stains hematoxylin and eosin. This classification has fallen into disuse, in favor of a classification based on what type of hormone is secreted by the tumor (though tumors which do not secrete any active hormone ("non-functioning tumors") are still sometimes called "chromophobic"). At present, classification of pituitary tumors is based on plasma hormone levels or immunohistochemical staining:

Type of adenoma	Secretion	Staining	Pathology
corticotrophic adenomas	secrete adrenocorticotropic hormone (ACTH) and pro-opiomelanocortin (POMC)	basophilic	Cushing's disease
somatotrophic adenomas	secrete growth hormone (GH)	acidophilic	acromegaly (gigantism)
thyrotrophic adenomas (rare)	secrete thyroid-stimulating hormone (TSH)	basophilic	occasionally hyperthyroidism, usually doesn't cause symptoms
gonadotrophic adenomas	secrete luteinizing hormone (LH), follicle-stimulating hormone (FSH) and their subunits	basophilic	usually doesn't cause symptoms
lactrotrophic adenomas or prolactinomas (most common)	secrete prolactin	acidophilic	galactorrhea, hypogonadism, amenorrhea, infertility, and impotence
null cell adenomas	do not secrete hormones	may stain positive for synaptophysin