Sometimes hypothyroidism occurs because of a pituitary gland disorder that may interfere with the production of thyroid stimulating hormone (TSH). This is fairly unusual, however. Tumors or cysts on the pituitary gland can also interfere with production of hormones from the gonads and the adrenal glands.
A common type of pituitary tumor is one that makes large quantities of a hormone called prolactin, known as a prolactinoma. These can occur in both men and women, often causing milk to come from the breasts or interfering with fertility. In most cases, prolactinomas are treated with medication to shrink them rather than surgery or radiation therapy. This may result in restoration of normal pituitary function, fixing the hypothyroidism.
The other common type of pituitary tumor is one that doesn't seem to produce any particular hormone in excess, merely blocking the normal hormone production of the pituitary gland. This type of pituitary tumor must be removed by a neurosurgeon, usually through an incision under the upper lip (a transsphenoidal hypophysectomy).
Often, tumors can recur, requiring external beam radiation therapy to prevent further enlargement. Rarely, some pituitary tumors make a hormone known as ACTH, causing Cushing's disease in which high levels of steroids (cortisol) are made. This dangerous condition is also treated by a transsphenoidal hypophysectomy, possibly resulting in hypothyroidism from pituitary damage. Many years ago, before improved obstetrical care, excessive loss of blood during childbirth could cause a drop in blood pressure that caused part of the pituitary to die and sometimes bleed, a condition known as Sheehan's syndrome. This can still happen to anyone with an unsuspected thyroid tumor who has a rapid drop in his or her blood pressure, resulting in destruction of the remaining pituitary, called pituitary apoplexy.
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