Indirect inguinal hernia: deep ring and inferior epigastric vessels
An indirect inguinal hernia is a protrusion of abdominal contents into the inguinal canal (the oblique passage through the lower abdominal wall) via its internal opening, the deep ring.
Remember
Ask where the hernia lies in relation to the inferior epigastric vessels (the artery and vein running up the inner surface of the lower abdominal wall): lateral to them and through the deep ring is indirect, while medial to them and through the back wall of the canal is direct.
The inferior epigastric vessels are the artery and vein running up the inner surface of the lower abdominal wall, and a surgeon uses them to classify a groin hernia. An indirect inguinal hernia lies lateral to them.
Its sac, a pouch of peritoneum (the thin lining of the abdominal cavity), enters the canal at the deep ring, which sits lateral to those vessels. The sac then follows the canal alongside the spermatic cord (the bundle of vessels, nerve and duct that supplies the testis) and may leave through the superficial ring, the external opening. A large sac can reach the scrotum, the place the testis descends into.
The processus vaginalis is a pouch of peritoneum that accompanies the testis as it descends and normally closes. The classic cause of an indirect hernia is failure of this pouch to regress (it normally degenerates), which gives the sac a ready-made path and is why the hernia is more common in younger patients. It is the more common inguinal type, about 80 percent of inguinal hernias.
A direct hernia is different. It is acquired when the abdominal wall weakens, so it pushes through the posterior wall of the canal at a weak area called Hesselbach's triangle, which lies medial to the vessels. It does not use the deep ring.
A scrotal swelling does not settle the type, because a large direct hernia can occasionally reach the scrotum too. A femoral hernia lies below the inguinal ligament (the band along the lower edge of the abdominal wall) and passes through the femoral canal (a passage outside the inguinal canal), appearing in the groin at the top of the inner thigh.
Key facts
- Landmark
- lateral to the inferior epigastric vessels
- Route
- in through the deep ring, then along the inguinal canal
- Scrotum
- a large sac can leave by the superficial ring and reach the scrotum, and a large direct hernia can occasionally reach it too
- Classic cause
- failure of the processus vaginalis to regress
- Frequency
- about 80 percent of inguinal hernias are indirect
- Direct contrast
- medial to the vessels, through the posterior wall of the canal in Hesselbach's triangle
- Men
- groin hernias occur about ten times more often in men than in women
Exam traps
- A sac that begins at the superficial ring is not indirect, even if it lies lateral to the vessels, because the sac enters at the deep ring; the superficial ring is where the canal ends.
- A sac medial to the inferior epigastric vessels does not enter the deep ring, because the deep ring lies lateral to the vessels; a medial sac is a direct hernia.
- A lateral sac that pushes through the posterior wall of the canal does not describe an indirect hernia, because pushing through the posterior wall is how a direct hernia behaves.
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