Omphalocele is similar to an umbilical hernia (See Pediatric Hernias). It is a larger defect of the umbilical ring into which the abdominal contents herniate. The size of these defects may be small with minimal bowel in the sac or large with the entire gastrointestinal tract and liver in the sac. Peritoneum covers the bowel. Gastroschisis is a defect of the abdominal wall usually to the right of the umbilical cord through which bowel herniates but there is no covering over the herniated bowel.

Anatomy

• The mid abdominal wall is composed of two large muscles (rectus abdominis) that run up and down and originate from the rib cage above and insert into the pubic bone below (Figure 1)
  
• The upper 3/4 of the rectus muscles are covered by a tough fascial sheath that lies in front and behind the muscles (Figure 2)
  
• The lower ¼ of the rectus muscles has only a tough sheath in front of the muscle
  
• The lateral abdominal wall muscles - external oblique, internal oblique and transverses abdominis muscles contribute to the sheath
  
• The muscle sheaths meet in a midline band called the linea alba
  
• Just below the middle of the linea alba is an opening called the umbilical ring where the umbilical cord entered the fetus

Figure 1 - Anatomy of the front wall of the abdomen. © C. Salici

Figure 2 - Anatomy of the front wall of the abdomen as seen from above. Note the various muscles (m) and fascia. © C. Salici