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 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|
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. The specific area of the visual pathway at which compression by these tumours occurs is at the optic chiasma.
The anatomy of this structure causes pressure on it to produce a defect in the temporal visual field on both sides, a condition called bitemporal hemianopia.
Tumors which cause visual difficulty are likely to be macroadenomata greater than 10 mm in diameter; tumors less than 10 mm are microadenomata.
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 options depend on the type of tumor and on its size:
- Prolactinomas are most often treated with bromocriptine or more recently, cabergoline which, unlike bromocriptine, decreases tumor size as well as alleviates symptoms, both dopamine agonists, 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.
- ^ a Chanson, Philippe; Weintraub, Bruce D.; and Harris, Alan G. (1993) Octreotide Therapy for Thyroid-Stimulating Hormone-Secreting Pituitary Adenomata. Annals of Internal Medicine 119 (3), 236-240.
- Cancer.gov: pituitary tumors
- Case report of Bilateral Hemianopsia Due to Pituitary Adenoma. Clinical Cases and Images.
- Medical Illustration of Pituitary Adenomas by Frank H. Netter