Abdominal Wall Anatomy

Abdominal Wall

• The anterolateral abdominal wall is divided into four quadrants and nine segments to describe the location of abdominal organs and associated pain.
• The four quadrants are divided by the horizontal transumbilical and vertical median planes.
• The nine abdominopelvic regions/segments are divided by the superior subcostal plane, inferior intertubercular plane, and two midclavicular planes.
• The regions include: hypochondriac, epigastric, flanks, umbilical, inguinal, and hypogastric regions.

Skin and Superficial Fascia

• The skin is the most superficial layer of the anterior abdominal wall.
• The superficial fascia is located just below the skin and consists of connective tissue.
• Inferior to the umbilicus, the superficial fascia is divided into two layers: Camper's fascia (fatty superficial layer) and Scarpa's fascia (deep layer).
• Camper's fascia is a thicker fatty layer that can have a variable degree of thickness and serves as a region of potential weakness in the abdominal wall.

Inguinal Canal

• The inguinal canal is located in the inguinal region, which extends from the lower abdomen into the medial part of the proximal thighs on each side.
• The canal ranges from 3-5 cm long in an adult and originates superolaterally at the deep inguinal ring.
• The deep inguinal ring is located 1.25 cm above the mid-inguinal point and is an oval opening in the transversalis fascia.
• The superficial inguinal ring is bordered medially by the inferolateral border of rectus abdominis, laterally by the inferior epigastric vessels, and inferiorly by the medial third of the inguinal ligament.
• The inguinal canal contains the spermatic cord and ilioinguinal nerve in males, and the round ligament of the uterus and ilioinguinal nerve in females.

Boundaries and Contents of Inguinal Canal

• The boundaries of the inguinal canal include the roof (transversalis fascia, internal oblique, and transversus abdominis), floor (inguinal ligament, lacunar ligament), anteriorly (aponeurosis of the external oblique muscle), and posteriorly (transversalis fascia).
• The contents of the spermatic cord include arteries (testicular, cremasteric, and ductus deferens), fascia (external spermatic, cremasteric, and internal spermatic), and nerves (genital branch of the genitofemoral nerve, sympathetic fibers, and ilioinguinal nerve).

Clinical Relations of Inguinal Canal

• Inguinal hernias can be divided into two main categories: indirect inguinal hernia (peritoneal sac enters the inguinal canal through the deep inguinal ring) and direct inguinal hernia (peritoneal sac enters the inguinal canal through the posterior wall).
• Both types of hernias can present as lumps in the scrotum or labia majora, and large herniations can occur through both the deep and superficial rings at the same time (Pantaloon hernias).
• Incarcerated hernias can become strangulated hernias, which contain non-viable bowel and can become necrotic, infected, and perforate if not treated.

Peritoneum

• The peritoneum is a double layer of peritoneal tissue that lines the abdominal cavity and covers the abdominal organs.
• The lesser sac communicates with the greater sac via the epiploic foramen of Winslow, located posterior to the free edge of the lesser omentum.
• The greater sac is divided into the supracolic and infracolic compartments by the transverse mesocolon.
• The supracolic compartment contains the liver, stomach, and spleen, while the infracolic compartment is divided by the root of the mesentery of the small intestine into the right and left infracolic spaces.
• The mesentery is a fold in the peritoneum that holds the organs in place from the back wall of the abdomen, and the omenta are two layers of peritoneum that have fused and extend from the stomach and proximal duodenum to neighboring organs.