A Spigelian hernia protrudes through a defect at the lateral edge of the rectus abdominis at the level of the arcuate line. What makes Spigelian hernias particularly dangerous?

• A They always present with a visible lump at the umbilicus
• B They are interparietal hernias and can strangulate without an obvious surface bulge ✓
• C They are the most common ventral hernias in women
• D They always communicate with the femoral canal

Explanation

Spigelian hernias are interparietal (intramural), passing through the semilunar line but remaining beneath the external oblique aponeurosis. The external oblique is intact, so the hernial sac tracks under the muscle, making the surface bulge absent or subtle. This concealment means strangulation can occur without a clinically obvious lump, delaying diagnosis. CT is the investigation of choice when Spigelian hernia is suspected clinically.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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