Boundaries and contents
The canal has an anterior wall, a posterior wall, a roof and a floor, and each is reinforced where the opposite wall is weakest.
| Wall | Formed by | Reinforced by |
|---|---|---|
| Anterior | Aponeurosis of external oblique | Internal oblique laterally, in front of the deep ring |
| Posterior | Transversalis fascia | Conjoint tendon medially, behind the superficial ring |
| Roof | Arching fibres of internal oblique and transversus abdominis | |
| Floor | Inguinal ligament | Lacunar ligament medially |
Deep inguinal ring: an opening in the transversalis fascia about 1–2 cm above the midpoint of the inguinal ligament (midway between the anterior superior iliac spine and the pubic tubercle), just lateral to the inferior epigastric vessels.
Superficial inguinal ring: a triangular gap in the external oblique aponeurosis above and lateral to the pubic tubercle, with medial and lateral crura held together by intercrural fibres.
Contents
In males the spermatic cord passes through the canal. It picks up three coverings as it goes: internal spermatic fascia from transversalis fascia at the deep ring, cremasteric muscle and fascia from internal oblique, and external spermatic fascia from external oblique at the superficial ring. Inside are the ductus deferens and its artery, the testicular artery, the cremasteric artery, the pampiniform venous plexus, lymphatics, the genital branch of the genitofemoral nerve and autonomic fibres. In females the round ligament of the uterus takes the same route to the labium majus.
The ilioinguinal nerve (L1) enters the canal by piercing internal oblique. It runs on the front of the cord, outside its fasciae, and leaves through the superficial ring.
Relations
The key relation of the canal is the inferior epigastric artery, which runs up medial to the deep ring and separates the two types of inguinal hernia.
The inguinal triangle (Hesselbach's triangle) lies on the posterior wall, bounded by the inferior epigastric vessels laterally, the lateral border of rectus abdominis medially and the inguinal ligament below. Its floor is transversalis fascia, reinforced medially by the conjoint tendon.
- Conjoint tendon: the fused lower aponeurotic fibres of internal oblique and transversus abdominis, inserting on the pubic crest and the medial pectineal line behind the superficial ring.
- Rectus abdominis: arises from the pubic crest and pubic symphysis and inserts on the xiphoid process and the fifth to seventh costal cartilages. It lies medial to the canal in the rectus sheath.
- Anterior rectus sheath: below the arcuate line, all three flat muscle aponeuroses pass in front of rectus, so only transversalis fascia lies behind it.
Below the inguinal ligament lies the femoral sheath, with the femoral canal as its most medial compartment.
Nerves and vessels
Three nerves of the first lumbar segment serve the region, and they are the ones at risk in hernia surgery.
| Nerve | Root | Course | Supply |
|---|---|---|---|
| Ilioinguinal | L1 | Through the canal on the front of the cord | Skin of upper medial thigh, root of penis and anterior scrotum, or mons and labium majus |
| Iliohypogastric | T12, L1 | Pierces external oblique aponeurosis above the superficial ring | Suprapubic skin; internal oblique and transversus |
| Genital branch of genitofemoral | L1, L2 | Within the cord | Cremaster; efferent limb of the cremasteric reflex |
The inferior epigastric artery arises from the external iliac artery just above the inguinal ligament and gives the cremasteric artery. The testicular artery arises from the aorta at about L2, and the artery to the ductus deferens usually comes from a vesical branch of the internal iliac artery.
Development and clinical relevance
The canal exists because the gonad descends from the posterior abdominal wall, dragging a peritoneal pouch, the processus vaginalis, and layers of the abdominal wall with it. The processus normally closes after birth, leaving the tunica vaginalis around the testis. Lymph from the testis still drains to the para-aortic nodes near its origin, not to the inguinal nodes.
| Feature | Indirect hernia | Direct hernia |
|---|---|---|
| Route | Through the deep ring along the canal | Through the posterior wall in Hesselbach's triangle |
| Relation to inferior epigastric vessels | Lateral | Medial |
| Cause | Patent processus vaginalis | Acquired weakness of the posterior wall |
| Reaches scrotum | Often | Rarely |
| Controlled by pressure over deep ring | Yes | No |
Indirect hernias are the commonest type in both sexes and at all ages. A femoral hernia emerges below the inguinal ligament, below and lateral to the pubic tubercle, whereas an inguinal hernia emerges above and medial to it. Entrapment of the ilioinguinal nerve during mesh repair causes chronic groin pain and numbness.
On the specimen
This station shows the canal opened by reflecting the external oblique aponeurosis, so the cord lies exposed on the inguinal ligament.
- Inguinal ligament: the rolled, gutter-shaped lower edge of the external oblique aponeurosis, running from the anterior superior iliac spine to the pubic tubercle.
- Spermatic cord: the rounded bundle on the floor of the canal; its outer covering at the superficial ring is the thin external spermatic fascia.
- Ilioinguinal nerve: the thin white nerve lying on the front of the cord. It is outside the cord coverings, which separates it from the genital branch of the genitofemoral nerve inside the cord.
- Internal oblique: the fleshy fibres arching over the cord laterally, forming part of the roof.
- Transversus aponeurosis and conjoint tendon: the tendinous sheet behind the cord medially, passing down to the pubic crest.
- Anterior rectus sheath and rectus abdominis: medial to the canal; the sheath is the aponeurotic layer over the vertical muscle.