Edema, hereditary angioneurotic: Localized skin swelling that results from an inherited deficiency of the C1 esterase inhibitor protein, which normally prevents activation of a cascade of proteins that leads to the occurrence of angioedema. Patients can develop recurrent attacks of swollen tissues, pain in the abdomen, and swelling of the voice box (larynx) that can compromise breathing. The diagnosis is confirmed when abnormally low levels of C1 esterase inhibitor are detected in the blood. Treatment options include antihistamines and male steroids (androgens). Also known as hereditary angioedema.