Pituitary adenoma classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ahmad Al Maradni, M.D. [2]

Overview

Pituitary adenoma may be classified according to the size of the adenoma and type of hormone secretion, subtypes include corticotrophic, somatotrophic, thyrotrophic, gonadotrophic, and lactrotrophic adenomas.

Classification

Pituitary tumors were, historically, classified 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 size, plasma hormone levels, or immunohistochemical staining.

Classification based on hormone secretion and 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

Classification based on the size of the adenoma

The radioanatomical classification places adenomas into 1 of 4 grades:

• Stage I are microadenomas (<1 cm) without sella expansion
• Stage II are macroadenomas (≥1 cm) and may extend above the sella
• Stage III are macroadenomas with enlargement and invasion of the floor or suprasellar extension
• Stage IV are macroadenomas that cause destruction of the sella