Anatomy of the anterior abdominal wall and fascial layers. Which one of the following is TRUE?
A. The aponeuroses all pass in front of the rectus muscle at the level of the umbilicusAnswer B
The anterior abdominal wall is made up of several layers including skin, superficial (Camper’s) and deep (Scarpa’s) fascia, muscle, extraperitoneal fascia and parietal peritoneum. Camper’s fascia is just beneath the skin and continuous with the superficial fat over the rest of the body. Scarpa’s fascia blends with the superficial layer superiorly and laterally but inferiorly it continues as the deep fascia of the thigh 1 cm below the inguinal ligament, and medially, it becomes Buck’s fascia. Colles’ fascia lines the scrotum (or labia majora) and perineum and inserts posteriorly to the edges of the urogenital diaphragm and inferior ischiopubic rami. The wall musculature consists of the outer external oblique, internal oblique and inner transversus abdominus. They play a role in respiration, movement and increase abdominal pressure during micturition, defaecation and childbirth. The external oblique originates from the anterior surface of the lower 8th rib and inserts inferiorly to the lateral half of the iliac crest and medially to the rectus sheath. Its fibres run lateral to medial. The internal oblique originates from the lumbodorsal fascia and iliac crest. Its fibres run at right angles to the external oblique, from medial to lateral, and the muscle inserts onto the anterior surface of the lower four ribs and the rectus sheath medially. Transversus abdominis originates from the lumbodorsal fascia and iliac crest and inserts medially into the rectus sheath. Its fibres run horizontally. The aponeuroses of the three muscles form the rectus sheath that surrounds the rectus abdominis muscle and they meet in the midline to form the avascular linea alba. The composition of the rectus sheath varies depending on the arbitrary arcuate line, which is a third of the way from the umbilicus to the pubic symphysis. Below the line, the aponeuroses of all three muscles pass in front of the rectus abdominis, leaving its posterior surface covered by transversalis fascia. Above the line, the rectus is covered anteriorly by the aponeuroses of the external and internal oblique, and posteriorly by the aponeuroses of internal oblique and transversus abdominis. The sheath is attached to the rectus abdominis anteriorly at segmental tendinous intersections.
Pyramidalis, when present, lies in front of the lower end of rectus abdominis that originates from the pubic symphysis and inserts into the linea alba. The inguinal canal lies parallel to and just above the inguinal ligament at the lower end of the anterior abdominal wall that transmits the ilioinguinal nerve and the spermatic cord (round ligament in women). It is 4 cm in length and extends medially and inferiorly from the deep (internal) to the superficial (external) inguinal rings. The boundaries of the canal include the inguinal ligament in the floor, the external oblique as the anterior wall (reinforced laterally by the internal oblique), mainly tranversalis fascia as the back wall and the roof by the conjoint tendon, which is formed from fusion of the lower fibres of internal oblique and transversus abdominis. The deep ring is an opening in the transversalis fascia that lies 1 cm above the inguinal ligament midway between the anterior superior iliac spine and pubic symphysis. The inferior epigastric artery lies medial to the ring. The superficial ring lies medial to and above the pubic tubercle and is an opening within the external oblique aponeurosis. The upper abdominal wall is supplied by the superior epigastric artery (branch of the internal thoracic artery) and the lower half by the deep circumflex iliac and inferior epigastric arteries (branches of the external iliac artery).