The anterior abdominal wall is a hexagonal area bounded superiorly by the xiphoid process and the costal margins. Inferiorly it extends along the iliac crests and narrows to the superior edge of the pubic bone in the midline. The inferolateral margins are defined by the inguinal ligaments bilaterally. Lateral extension occurs posteriorly to the muscles adjacent to the lumbar spine.
The most superficial layers of the abdominal wall are the skin and the subcutaneous tissue. The subcutaneous tissue is comprised of deep and superficial adipose tissue layers separated by fibrous tissue matrices. Camper’s fascia is the superficial fatty layer and Scarpa’s fascia is a more membranous layer that will eventually become contiguous with the superficial fascia of the back, thorax, and fascia lata of the thigh.
The abdominal wall can be divided into midline and anterolateral groups of muscles. The main lateral muscles of the anterior abdominal wall are, from exterior to interior, the external oblique, internal oblique, and transversus abdominis. The rectus abdominis and the pyramidalis muscles comprise the midline group, although the presence of the pyramidalis is not consistent among the population (absent in 15% of individuals).
The aponeuroses of the lateral muscles form the sheath of the rectus (anterior and posterior above the arcuate line, and only anterior below) and the linea alba is the midline decussation of the three aponeuroses.
The transversalis fascia is a weak fibrous layer covering the inner surface of the transversus abdominis muscles and is separated from the peritoneum by a layer of fat, commonly known as the preperitoneal fat layer.
The peculiar anatomy of the inguinal region, characterized by the passage of neurovascular structures from the abdominal cavity to the genital region and the lower limbs, determines the high incidence of herniary pathology at this level. A thorough knowledge of the anatomy of this region is mandatory to properly understand the pathophysiology and treatment of inguinal hernias.
The inguinal canal is an oblique rift approximately 4 to 6 cm long in the lower part of the anterior abdominal wall and it contains the spermatic cord in males and the round ligament of the uterus in females. It is located above the inguinal ligament and between the opening of the external (superficial) and the internal (deep) inguinal rings. The is a triangular opening formed by the medial fibers of the external oblique aponeurosis that lies just lateral to the pubic tubercle. The internal ring is a normal defect in the transversalis fascia shaped like an inverted U. Its arms (anterior and posterior) are a special thickening of the transversalis fascia forming a sling.
The boundaries of the inguinal canal are formed by:
– Superior wall: the arched fibers of the lower edge of the internal oblique muscle and transversus abdominis muscles and their aponeuroses.
– Inferior wall: the inguinal and lacunar ligaments.
– Anterior wall: the aponeurosis of the external oblique and, more laterally, by involvement of the internal oblique muscle.
– Posterior wall (“floor”): it is the most important wall of the inguinal canal. It is formed by fusion of the aponeurosis of the transversus abdominis muscle and the transversalis fascia in 75% of the population (forming a strong wall), and only by the transversalis fascia in the remaining individuals (yielding a weak wall, more prone to hernias).
The inguinal ligament is the incurved free edge of the external oblique aponeurosis between its origin on the anterior superior iliac spine and its insertion at the pubis. The middle third of the ligament has a free edge and the rest is strongly attached to the iliopsoas fascia. It is important because of its role as both a landmark and an integral component of many groin hernia repairs.
The inguinal ligament continues downward to the superior pubic ramus to form the lacunar ligament (Gimbernat’s ligament) and laterally along the pectineal line as the pectineal ligament (Cooper’s ligament).
Myopectineal orifice of Fruchard
The myopectineal orifice was first described by Fruchard in 1956 and it corresponds to the common locations for rising of all hernias in the inguino-crural region. This area is bounded as follows:
– Superiorly: arch of the internal oblique muscle and transversus abdominis muscle (transverse arch).
– Laterally: iliopsoas muscle.
– Medially: lateral border of the rectus abdominis muscle and its anterior lamina.
– Inferiorly: Cooper’s ligament.
The inguinal ligament bridges and divides this framework into the inguinal region above and the femoral region below.
The inguinal (Hesselbach) triangle was described by Hesselbach in 1814 and it is formed by the lateral border of rectus abdominis sheath medially, the inferior (deep) epigastric vessels superolaterally, and the inguinal ligament at the base. This area is only covered by the peritoneum and the transversalis fascia, which makes it a weak area and the site of occurrence of direct inguinal hernias. The aponeurotic arch that is formed from the transversus abdominis muscles crosses the apex of this triangle and provides reinforcement for this weak area.