Direct versus indirect inguinal hernia
An inguinal (groin) hernia is tissue pushing through the wall that normally contains it: a direct one goes straight through, an indirect one takes the long route.
Remember
The inferior epigastric vessels (an artery and vein on the deep surface of rectus abdominis) separate the two routes. An indirect hernia enters at the deep ring (the inner entrance to the canal), lateral to those vessels, whereas a direct hernia pushes through Hesselbach triangle (a weak area in the back wall of the canal), medial to them.
In an inguinal hernia, abdominal content leaves the cavity through a weakness linked to the inguinal canal, a short passage through the lower abdominal wall. The canal begins at the deep ring, its inner entrance, and ends at the superficial ring, its outer opening.
The inferior epigastric vessels are the landmark that divides the two classical paths. An indirect hernia enters at the deep ring, lateral to those vessels (on their outer side), and travels along the canal. It is usually due to a processus vaginalis, a pouch of peritoneum (the lining of the abdominal cavity) that accompanies the testis down, failing to close. An indirect hernia is called congenital in mechanism, meaning its defect is present from development, even though it can stay silent until adult life.
A direct hernia instead pushes straight through the weak back wall of the canal, in Hesselbach triangle, medial to the vessels (towards the midline). The triangle is bordered by the vessels, the lateral edge of rectus abdominis and the inguinal ligament (the fibrous band forming the floor of the canal). A direct hernia is acquired, usually appearing in adulthood.
Both types can end up as a lump near the superficial ring, so the type depends on the point of entry and not on where the lump appears. A femoral hernia is a different hernia: it passes below the inguinal ligament into the thigh, not through the inguinal canal.
Key facts
- Indirect route
- Enters at the deep ring, lateral to the inferior epigastric vessels, and follows the canal.
- Direct route
- Bulges through the posterior wall in Hesselbach triangle, medial to the vessels.
- Indirect cause
- Usually a processus vaginalis that has failed to close.
- Direct cause
- An acquired weakness of the back wall of the canal, usually appearing in adulthood.
- Triangle borders
- The lateral edge of rectus abdominis, the inguinal ligament and the inferior epigastric vessels.
- Superficial ring
- A direct hernia may bulge into the superficial ring, but it does not start at the deep ring.
- Femoral hernia
- Inguinal hernias lie above the inguinal ligament, whereas a hernia below it in the femoral canal (which lies medial to the femoral vein) is a femoral hernia.
Exam traps
- The superficial ring is where an indirect hernia can leave the canal, not where it enters; it enters at the deep ring.
- A direct hernia does not enter at the deep ring, as an indirect hernia does; it bulges through the posterior wall of the canal instead.
- An acquired weakness of the posterior wall at Hesselbach triangle explains a direct hernia, which usually presents in adulthood and is not congenital, rather than the pathway of an indirect hernia.
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