These tumors produce excessive growth hormone and compress surrounding brain tissues as they grow larger. In some cases, they may compress the optic nerves. Expansion of the tumor may cause headaches and visual disturbances. In addition, compression of the surrounding normal pituitary tissue can alter production of other hormones, leading to changes in menstruation and breast discharge in women and impotence in men because of reduced testosterone production.A marked variation in rates of GH production and the aggressiveness of the tumor occurs. Some adenomas grow slowly and symptoms of GH excess are often not noticed for many years. Other adenomas grow rapidly and invade surrounding brain areas or the sinuses, which are located near the pituitary. In general, younger people tend to have more aggressive tumors.Most pituitary tumors arise spontaneously and are not genetically inherited. Many pituitary tumors arise from a genetic alteration in a single pituitary cell that leads to increased cell division and tumor formation. This genetic change, or mutation, is not present at birth but is acquired during life. The mutation occurs in a gene that regulates the transmission of chemical signals within pituitary cells; it permanently switches on the signal that tells the cell to divide and secrete growth hormones. The events within the cell that cause disordered pituitary cell growth and GH oversecretion currently are the subject of intensive research.Pituitary adenomas and diffuse somatomammotroph hyperplasia may result from somatic mutations activating GNAS, which may be acquired or associated with McCune-Albright syndrome.
The first is endonasal transsphenoidal surgery, which involves the surgeon reaching the pituitary through an incision in the nasal cavity wall. The wall is reached by passing through the nostrils with microsurgical instruments. The second method is transsphenoidal surgery during which an incision is made into the gum beneath the upper lip. Further incisions are made to cut through the septum to reach the nasal cavity, where the pituitary is located. Endonasal transsphenoidal surgery is a less invasive procedure with a shorter recovery time than the older method of transsphenoidal surgery, and the likelihood of removing the entire tumor is greater with reduced side effects. Consequently, endonasal transsphenoidal surgery is the more common surgical choice.These procedures normally relieve the pressure on the surrounding brain regions and lead to a lowering of GH levels. Surgery is most successful in people with blood GH levels below 40 ng/ml before the operation and with pituitary tumors no larger than 10 mm in diameter. Success depends on the skill and experience of the surgeon. The success rate also depends on what level of GH is defined as a cure. The best measure of surgical success is the normalization of GH and IGF-1 levels. Ideally, GH should be less than 2 ng/ml after an oral glucose load. A review of GH levels in 1,360 people worldwide immediately after surgery revealed that 60% had random GH levels below 5 ng/ml.