hernia, protrusion of an internal organ or part of an organ through the wall of a body cavity. The hernia is enclosed by a sac formed by the lining of the cavity. It results from a weakness or rupture in the wall, usually where there is already a natural weakness. A hernia may be present at birth or acquired later in life after heavy strain on the musculature. Structurally weak points, e.g., where various blood vessels, nerves, and ducts enter or leave a body cavity, occur in areas such as the lower abdomen, the diaphragm, and the region around the navel. If the protruding structure is caught in the muscular aperture of the wall, the result is a strangulation of the part, or an incarcerated hernia. Prompt medical attention must be received or loss of blood and eventual gangrene may result. A small hernia usually bulges spontaneously under exercise and strain and recedes into the cavity when the subject relaxes. A truss or external pad held against the weak spot may be used to control a hernia. However, surgery is usually recommended, even for a mild hernia, since it may eventually enlarge.