Abnormal growths that arise in the pituitary gland located at the base of the brain. Most pituitary tumors are not malignant. However, they can enlarge and damage nearby tissue. Symptoms of a pituitary tumor include headache, seizures, personality changes, visual disturbances, drooping eyelids, weakness, lethargy, irritability, and cold intolerance. Some pituitary tumors secrete an excess of hormones leading to gigantism or acromegaly (from excess of growth hormone), hyperthyroidism, or Cushing syndrome.