Any disease process or injury that can damage the pituitary can cause pituitary failure. The most common problem is a tumor of the pituitary gland. These are common and almost always benign. In most cases they do not cause pituitary failure, and it is much more common that they either cause no symptoms or cause over-production of one or more pituitary hormones. If a tumor is very large, however, it may cause failure of pituitary function by compressing or displacing the normal tissue.
Pituitary surgery is itself a common cause of pituitary failure. If a pituitary tumor has to be removed surgically, there is damage or destruction of the remaining pituitary tissue, and the gland may not function properly. The same is true for radiation therapy. In this case pituitary failure may happen gradually, often over the space of several years after the radiation was given.
Pituitary infarction is a common cause of pituitary failure. "Infarction" means death because the blood supply is cut off. Pituitary infarction most often occurs in settings where there is a sudden drop in blood pressure. The blood flow to the pituitary gland is somewhat tenuous, and an abrupt fall in blood pressure may cause the gland to die from inadequate blood flow with the oxygen and nutrients necessary to keep the tissue alive. A common situation in which this occurs in if there is hemorrhage with childbirth. In pregnancy the pituitary gland enlarges. If there is hemorrhage with delivery, blood flow may be cut off at a time when the pituitary gland is vulnerable. Pituitary failure following this is called "Sheehan’s syndrome."
An accident with head trauma or even sudden severe movement of the head may cause pituitary failure. The blood vessels to the gland may be torn in this setting and the gland may die as a result.
The final common cause of pituitary failure is an autoimmune disease that damages or destroys pituitary tissue. This is less common than in some other endocrine organs, such as the thyroid, where under- or over-activity may result, or the insulin-producing cells of the pancreas, where type 1 diabetes is the consequence. But an autoimmune process affecting the entire pituitary, or in some cases just one hormone, is now well recognized as a problem.
Other, less common causes of pituitary failure can occur, including metastatic tumors to the gland, infection of the pituitary or surrounding tissue, or certain "granulomatous" diseases.
More Answers from Jack Merendino, MD