Define a hernia and the terms reducible, incarcerated, obstructed and strangulated.

A hernia is protrusion of a viscus (or part of it) through a defect in the wall of its containing cavity. Reducible: returns to the cavity. Incarcerated: irreducible but viable. Obstructed: lumen blocked. Strangulated: blood supply compromised - ischaemic, the surgical emergency.

Clinical relevance. Distinguishing incarceration from strangulation decides whether surgery is urgent or emergent.

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Hernia terminology

Precise terms describe how far a hernia has progressed and how urgently it must be treated.

Definitions

• Hernia: protrusion of a viscus or tissue through an abnormal defect in its containing wall.
• Reducible: contents return to the abdomen spontaneously or with pressure.
• Irreducible / incarcerated: contents cannot be reduced but remain viable, usually from adhesions or a narrow neck.
• Obstructed: the lumen of contained bowel is blocked, causing intestinal obstruction.
• Strangulated: the blood supply of the contents is cut off, leading to ischaemia, gangrene, and perforation - a surgical emergency.

Parts of a hernia

• Sac (peritoneal outpouching), neck (the defect), and contents (omentum, bowel, etc.).
• A narrow neck (femoral, para-umbilical) predisposes to strangulation.