hypopituitarism, deficiency of pituitary hormones caused by damage to the pituitary gland. Patients may have a deficiency of one or all pituitary hormones, including vasopressin (antidiuretic hormone), the hormone of the posterior pituitary gland that controls the excretion of urine. Deficiency of all pituitary hormones is known as panhypopituitarism. Pituitary hormone deficiencies can occur as a result of pituitary disease or hypothalamic disease, with deficiency of the hypothalamic hormones that stimulate the secretion of most pituitary hormones. The causes of hypopituitarism include pituitary and hypothalamic tumours, infections, postpartum pituitary hemorrhage (Sheehan syndrome), and surgery for secreting or nonsecreting pituitary tumours (see pituitary gland).