Topography and Direction
Topographically, the inguinal canal is located in the lowest regions of the anterolateral abdominal wall. This anatomical structure has a clearly defined oblique direction. Its spatial vector can be described as lateromedial and craniocaudal. Tracing the course of the canal from the superficial inguinal ring, it runs posteriorly, superiorly, and laterally to reach the deep inguinal ring.
The total length of this slit-like space in an adult is approximately 4–5 centimeters. A critical external landmark is the inguinal ligament (ligamentum inguinale), which stretches between the anterior superior iliac spine (spina iliaca anterior superior) and the pubic tubercle. The canal lies parallel to this ligament, running 1.0–1.5 cm superior to it.
Four Walls of the Canal
Like any tubular or slit-like structure in surgical anatomy, the inguinal canal has four walls formed by the layers of the abdominal wall:
- Anterior wall — formed by the aponeurosis of the external oblique muscle. In its lateral part, this wall is additionally reinforced by the muscle fibers of the internal oblique muscle.
- Posterior wall — represented by the transversalis fascia (fascia transversalis). To provide structural integrity, the posterior wall is reinforced medially by the conjoined tendon (falx inguinalis), which is formed by the fused aponeuroses of the internal oblique and transversus abdominis muscles. Additionally, the intervein ligament (ligamentum interfoveolare) blends here.
- Superior wall (roof) — created by the free, arching lower muscular edges of the internal oblique and transversus abdominis muscles.
- Inferior wall (floor) — represented by the grooved, infolded inguinal ligament (ligamentum inguinale). Near its medial end, close to the pubic tubercle, it transitions smoothly into the lacunar ligament (ligamentum lacunare).
Anatomy of the Inguinal Rings
Entry into and exit from the canal occur through two distinct anatomical openings:
Superficial Inguinal Ring (anulus inguinalis superficialis) This serves as the exit of the canal and is a triangular defect in the aponeurosis of the external oblique muscle located directly superior to the pubic tubercle. The margins of this opening form two crura: medial and lateral (crus mediale et laterale). Superiorly, these crura are interconnected and reinforced by intercrural fibers (fibrae intercrurales). This is the ring palpated during a physical examination. The external spermatic fascia originates from the outer margins of the canal at this level.
Deep Inguinal Ring (anulus inguinalis profundus) This serves as the entrance to the canal and appears as an oval-shaped depression or defect in the transversalis fascia. Its approximate dimensions are 2.5–3.0 cm by 1.0–2.5 cm. A vital topographic landmark: the deep ring lies strictly lateral to the inferior epigastric vessels (arteria et vena epigastricae inferiores). The margins of the ring are thickened, and its lateral border blends with the ligamentum interfoveolare. The internal spermatic fascia originates here.
> Important Surgical Note: During the surgical repair of incarcerated hernias, when it becomes necessary to cut the deep inguinal ring, the surgeon must remember the medially positioned inferior epigastric vessels to avoid catastrophic vascular injury.
Contents and Origin of Coverings
The contents of the muscular-fascial cleft differ fundamentally between sexes.
In males, the canal transmits the spermatic cord (funiculus spermaticus) along with the cremaster muscle. The spermatic cord contains a complex arrangement of structures:
- Ductus deferens (vas deferens);
- Testicular artery (arteria testicularis);
- Pampiniform venous plexus (plexus pampiniformis);
- Cremasteric artery and vein;
- Artery of the ductus deferens;
- Lymphatic vessels;
- Genital branch of the genitofemoral nerve (ramus genitalis nervi genitofemoralis);
- Sympathetic and parasympathetic nerve fibers.
In females, the inguinal canal contains the round ligament of the uterus (ligamentum teres uteri), accompanied by a small neurovascular bundle.
During embryonic testicular descent, the layers of the abdominal wall are dragged along, forming the coverings of the spermatic cord:
- External spermatic fascia — derived from the aponeurosis of the external oblique muscle at the superficial ring.
- Cremaster muscle and fascia (musculus et fascia cremasterica) — derived from the lower muscular fibers of the internal oblique muscle.
- Internal spermatic fascia — derived from the transversalis fascia (fascia transversalis) at the level of the deep ring.