inguinal canal

The inguinal canal runs parallel and superior to the inguinal ligament, extending from the deep inguinal ring (a defect in the transversalis fascia, lateral to the inferior epigastric vessels) to the superficial inguinal ring (an opening in the external oblique aponeurosis, located superolateral to the pubic tubercle). Its walls are formed by four layers: anteriorly by the external oblique aponeurosis (reinforced laterally by internal oblique), posteriorly by the transversalis fascia (reinforced medially by the conjoint tendon), superiorly (roof) by the arching fibers of internal oblique and transversus abdominis, and inferiorly (floor) by the inguinal ligament (and lacunar ligament medially).

During embryologic development, the canal forms as a result of the testes descending from the posterior abdominal wall into the scrotum, guided by the gubernaculum, dragging peritoneum (forming processus vaginalis) and layers of the abdominal wall with it. In females, the canal is smaller and transmits the round ligament of the uterus.

Clinical significance: The canal is a site of anatomic weakness. Indirect inguinal hernias occur through the deep inguinal ring, lateral to the inferior epigastric vessels, following the path of the processus vaginalis—more common in infants and young males due to failure of processus vaginalis closure. Direct inguinal hernias protrude through Hesselbach's triangle (bounded by inferior epigastric vessels laterally, rectus abdominis medially, and inguinal ligament inferiorly), medial to the inferior epigastric vessels, due to weakness in the transversalis fascia—more common in older men. Both types exit through the superficial inguinal ring and are covered by the same layers as the spermatic cord if they follow the canal. Hydroceles and varicoceles also relate to structures within the canal. Understanding the relationship of the inferior epigastric vessels helps differentiate direct versus indirect hernias on exam and imaging.