Clinical meaning
Panhypopituitarism is deficiency of all anterior pituitary hormones (ACTH, TSH, LH/FSH, GH, prolactin) ± posterior pituitary (ADH — central diabetes insipidus). The anterior pituitary has a characteristic vulnerability pattern based on cell location and vascular supply: gonadotrophs (LH/FSH) are most vulnerable and lost first, followed by somatotrophs (GH), thyrotrophs (TSH), and corticotrophs (ACTH) — thus the mnemonic 'Go Look For The Adenoma' reflects the order of hormone loss. Causes include pituitary tumors (most common — non-functioning adenoma), surgical resection, radiation therapy, Sheehan syndrome (postpartum pituitary necrosis from hemorrhagic shock), pituitary apoplexy (hemorrhage into adenoma), autoimmune hypophysitis (including checkpoint inhibitor-induced), infiltrative disease (sarcoidosis, hemochromatosis, histiocytosis), and traumatic brain injury (TBI — 12-15% develop hypopituitarism). The clinical presentation depends on the number and severity of hormone deficits: ACTH deficiency is the most acutely dangerous (adrenal crisis), TSH deficiency causes secondary hypothyroidism, and gonadotropin deficiency causes hypogonadism.