Incisional hernia and failed fascial healing
An incisional hernia is a hernia (a protrusion of tissue through a gap in the wall that holds it in) at the scar of an earlier operation.
Remember
Poor healing of the fascia (the tough connective-tissue sheet that gives the abdominal wall its strength) at an operation scar leaves a weak point, and raised pressure inside the abdomen then pushes contents through it.
Memory aid
Think of the scar as the darned heel of a sock: the repair is the part most likely to wear thin.
Use it to remember that the hernia follows the repaired scar, because the repair is the weakest part of the wall.
An incisional hernia is a hernia that forms through the scar of a previous operation, so by definition it occurs after an operation. It is acquired, which means it is not a congenital defect.
The layer that matters is the fascia, the tough connective-tissue sheet that gives the abdominal wall most of its strength. A laparotomy (an operation that opens the abdomen) cuts through the fascia, and the stitches hold the cut edges together while the fascia heals. Fascia heals slowly, and complications in wound healing can leave a weak or gapped scar. If the scar does not regain enough tensile strength (the ability to resist being pulled apart), the repair stays the weakest part of the wall.
Once the scar is weak, coughing, straining or lifting raises the pressure inside the abdomen and pushes abdominal contents into the gap. With the skin intact, the contents simply push out beneath it, so the swelling follows the old incision. The swelling is typically a soft, reducible lump, which can be pushed back or shrinks when the patient lies down. It bulges more on coughing.
Midline incision, emergency surgery, wound infection, obesity and diabetes raise the risk. A lump that becomes painful, tender or impossible to push back in is a different problem: trapped contents can lose their blood supply (strangulation), which is a surgical emergency.
Key facts
- Definition
- an acquired hernia through weakened abdominal wall at the scar of a previous operation.
- Mechanism
- cut fascia that does not regain enough strength leaves a weak scar, and raised pressure inside the abdomen pushes contents through it.
- Typical findings
- a soft, reducible (able to be pushed back) swelling at or near the scar that enlarges on coughing.
- Risk factors
- emergency surgery, obesity, midline incision, wound infection, diabetes, steroid use and smoking.
- Location
- the hernia lies at the previous incision, unlike primary hernias, which form at natural weak points such as the groin.
- Red flag
- pain, tenderness or a lump that cannot be pushed back in needs urgent assessment.
Exam traps
- Isolated failure of peritoneal healing (the peritoneum is the membrane lining the abdomen) does not explain an incisional hernia, because the peritoneum is not the main load-bearing layer of the wall; the fascial closure has to fail.
- Thinning of the skin and fat over a scar, on its own, does not produce an incisional hernia, because the closure that has to withstand pressure inside the abdomen is the fascial one.
- A femoral hernia passes through the femoral canal in the upper thigh and presents as a groin lump, so it does not account for a bulge in an abdominal scar.
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