Pituitary apoplexy is attached to the hypothalamus, a part of the brain, by a stalk that also contains the blood vessels that supply the gland. It is unclear why pituitary tumors are five times more likely to bleed than other tumors in the brain. There are various proposed mechanisms by which a tumor can increase the risk of either infarction (insufficient blood supply leading to tissue dysfunction) or hemorrhage. The pituitary gland normally derives its blood supply from vessels that pass through the hypothalamus, but tumors develop a blood supply from the nearby inferior hypophyseal artery that generates a higher blood pressure,
Pituitary adenoma interacting protein" ("AIP") gene , and duplications in chromosome Xq26.3 that include the "GPR101" gene that also causes X-linked acrogigantism (X-LAG) syndrome. About 15-20% of FIPA families carry a germline "AIP" gene mutation or deletion, and the disease occurs as autosomal dominant with incomplete penetrance, meaning that about 20% of AIP mutation carriers will develop a pituitary adenoma. "AIP" mutation associated pituitary adenomas (either presenting as FIPA or as individual, non familial cases) are usually growth hormone secreting (acromegaly) or prolactin secreting (prolactinoma) adenomas that are large (macroadenomas) and often occur in children, adolescents and young adults. Daly and colleagues