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.

Types

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:

• corticotrophic adenomas secrete adrenocorticotropic hormone (ACTH) and pro-opiomelanocortin (POMC)
• somatotrophic adenomas secrete growth hormone (GH)
• thyrotrophic adenomas secrete thyroid-stimulating hormone (TSH)

This is a rare tumor type, making up <1% of all pituitary adenomas. TSH secretion from these tumors can cause hyperthroidism.

• gonadotrophic adenomas secrete luteinizing hormone (LH), follicle-stimulating hormone (FSH) and their subunits
• lactrotrophic adenomas or prolactinomas secrete prolactin
• null cell adenomas do not secrete hormones, but may stain positive for synaptophysin

Diagnosis

The diagnosis is generally entertained either on the basis of visual difficulties arising from the compression of the optic nerve by the tumor, or on the basis of manifestations of excess hormone secretion: the specifics depend on the type of hormone. Tumors which cause visual difficulty are likety to be macroadenomas greater than 10 mm in diameter; tumors less than 10 mm are microadenomas.

The most common secretory pituitary tumor is the prolactinoma, which can cause galactorrhea, hypogonadism, amenorrhea, infertility, and impotence. GH-secreting tumors cause acromegaly (gigantism). Corticotrophic adenomas cause Cushing's disease. TSH-secreting adenomas can, rarely, cause hyperthyroidism. Tumors which secrete LH, FSH or TSH most often don't cause symptoms because of that hormone secretion. Some tumors secrete more than one hormone, the most common combination being GH and prolactin.

Prolactinomas are frequently diagnosed during pregnancy, when the hormone progesterone increases the tumor's growth rate.

Headaches may be present.

The diagnosis is confirmed by testing hormone levels, and by radiographic imaging of the pituitary (for example, by CT scan or MRI).

Treatment

Treatment options depend on the type of tumor and on its size. Prolactinomas are most often treated with bromocriptine, a dopamine agonist, and followed by serial imaging to detect any increase in size. Treatment where the tumor is large can be with radiation therapy or surgery, and patients generally respond well. Efforts have been made to use a progesterone antagonist for the treatment of prolactinomas, but so far have not proved successful. Thyrotrophic adenomas respond to octreotide, a long-acting somatostatin analog, in many but not all cases according to a review of the medical literature. Unlike prolactinomas, thyrotrophic adenomas characteristically respond poorly to dopamine agonist treatment.^{Octreotide Therapy for Thyroid-Stimulating Hormone-Secreting Pituitary Adenomas. Annals of Internal Medicine 119 (3), 236-240.}

1. ^  See Note # 1.