Pituitary Tumor

The pituitary gland — a pea-sized endocrine organ nestled within a bony recess at the base of the skull called the sella turcica — produces and regulates a remarkable range of hormones that govern body growth, metabolism, reproductive function, the stress response, water balance, and thyroid activity. Pituitary tumors are among the most common intracranial tumors, and often detectable incidentally on autopsy studies. The great majority are benign and do not spread, but they can cause significant illness through hormonal overproduction, hormonal deficiency, or compression of nearby structures.

Pituitary tumors require a multidisciplinary approach involving neurosurgery, endocrinology, and ophthalmology, as optimal management addresses both the tumor itself and its hormonal consequences.

Pituitary tumors are classified in several complementary ways. By hormonal function, they are divided into functioning (hormone-secreting) and non-functioning adenomas.

• Prolactinomas — tumors that overproduce the hormone prolactin — are the most common functioning type.
• Acromegaly is caused by a growth hormone-secreting adenoma; when this occurs before growth plate closure in adolescents, the condition is called gigantism.
• Cushing's disease results from adrenal glands producing excessive cortisol.
• Rarer types include TSH-secreting and gonadotropin-secreting adenomas.
• Non-functioning adenomas produce no active hormone and come to clinical attention through mass effects on surrounding structures.

By size, adenomas less than 10 mm in diameter are called microadenomas; those 10 mm or larger are called macroadenomas. Macroadenomas are more likely to cause visual symptoms and hormonal deficiencies through compression of the optic chiasm and surrounding pituitary tissue.

Symptoms arise from two main mechanisms: the direct hormonal effects of a secreting tumor, and the physical pressure exerted by a growing tumor on adjacent structures.

Hormone-related symptoms depend on the tumor type. Prolactinoma causes irregular or absent menstrual periods, galactorrhea (unexpected milk production), and infertility in women; in men, it produces reduced libido, erectile dysfunction, and infertility. Growth hormone excess produces gradual enlargement of the hands, feet, and facial features, jaw widening, spacing of the teeth, excessive sweating, joint pain, and an increased risk of sleep apnea and diabetes. Cushing's disease produces weight gain with characteristic central obesity, a fatty "buffalo hump" between the shoulders, a rounded "moon face," purple stretch marks, easy bruising, muscle weakness, high blood pressure, and diabetes.

Mass effects from larger tumors include bitemporal hemianopia — the classic pattern of visual field loss caused by upward compression of the optic chiasm — as well as headache, double vision from cranial nerve involvement in the cavernous sinus, and hypopituitarism (deficiency of one or more pituitary hormones) caused by compression of normal pituitary tissue.

The vast majority of pituitary adenomas arise sporadically from acquired somatic mutations in individual pituitary cells, without a hereditary predisposition. The precise molecular events driving adenoma formation are still under investigation, though mutations in genes regulating cell-cycle control and hormone receptor signaling play a role.