Hypopituitarism usually results from a deficiency of anterior pituitary hormones or, rarely, from tissue resistance to these hormones. Deficiency may be from primary pituitary disease, pituitary stalk disorders, hypothalamic disease, or an extrasellar disorder impinging on, or infiltrating, the hypothalamic-pituitary unit. Primary pituitary disease results from the loss of anterior pituitary cells and may be congenital or acquired. Common causes are pituitary tumors and their surgical or radiotherapeutic ablation. Infrequent causes include pituitary infarction (eg, postpartum pituitary necrosis, also known as Sheehan syndrome), pituitary apoplexy, lymphocytic hypophysitis, infiltrative diseases (eg, hemochromatosis), and metastatic disease (eg, from breast or lung).
