Abdominal Wall

Abdominal Wall S. Patel, MD

 The abdominal wall is defined superiorly

by the costal margins, inferiorly by the symphysis pubis and pelvic bones, and posteriorly by the vertebral column

The muscle fibers of the rectus abdominus are arranged vertically and are encased within an aponeurotic sheath, the anterior and posterior layers of which are fused in the midline at the linea alba The rectus abdominus has insertions on the symphysis pubis and pubic bones, on the anteroinferior aspects of the fifth and sixth ribs, as well as the seventh costal cartilage and the xiphoid process The lateral border of the rectus muscles assumes a convex shape that gives rise to the surface landmark, the linea semilunaris.

The three muscular layers of the abdominal wall lateral to the rectus abdominus are the external oblique, internal oblique, and transversus abdominus muscles

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Above the arcuate line: 

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the anterior rectus sheath is formed by the external oblique aponeurosis and the external lamina of the internal oblique aponeurosis the posterior rectus sheath is formed by the internal lamina of the internal oblique aponeurosis, the transversus abdominis aponeurosis, and the transversalis fascia

Below the arcuate line: 

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the anterior rectus sheath is formed by the external oblique aponeurosis, the laminae of the internal oblique aponeurosis, and the transversus abdominis aponeurosis There is no aponeurotic posterior covering of this lower portion of the rectus muscles, although the transversalis fascia remains a contiguous structure on the posterior aspect of the abdominal wall in this area as well

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Majority of the blood supply to the muscles of the anterior abdominal wall is derived from the superior and inferior epigastric arteries The superior epigastric artery arises from the internal thoracic artery The inferior epigastric artery arises from the external iliac artery A collateral network of branches of the subcostal and lumbar arteries also contributes to the abdominal wall blood supply

Congenital Abnormalities 

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Prominent in the early embryonic abdominal wall is a large central defect through which pass the vitelline (omphalomesenteric) duct and allantois The vitelline duct connects the embryonic and fetal midgut to the yolk sac During the sixth week of development, the abdominal contents grow too large for the abdominal wall to contain and the embryonic midgut herniates into the umbilical cord While outside the confines of the developing abdomen, it undergoes a 270-degree counterclockwise rotation, and at the end of the twelfth week returns to the abdominal cavity.

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Complete failure of the vitelline duct to regress results in a vitelline duct fistula, which is associated with drainage of small intestinal contents from the umbilicus. If both the intestinal and umbilical ends of the vitelline duct regress into fibrous cords, a central vitelline duct (omphalomesenteric) cyst may occur Persistent vitelline duct remnants between the gastrointestinal tract and the anterior abdominal wall may be associated with small intestinal volvulus in neonates When diagnosed, vitelline duct fistulas and cysts should be excised along with any accompanying fibrous cord

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Urachus is a fibromuscular, tubular extension of the allantois that develops with the descent of the bladder to its pelvic position Persistence of urachal remnants can result in cysts as well as fistulas to the urinary bladder, with drainage of urine from the umbilicus. These are treated by urachal excision and closure of any bladder defect that may be present

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Rectus abdominis diastasis (or diastasis recti) describes a clinically evident separation of the rectus abdominus muscle pillars, generally as a result of decreased tone of the abdominal musculature The characteristic bulging of the abdominal wall in the epigastrium is sometimes mistaken for a ventral hernia Diastasis may be congenital, as a result of a more lateral insertion of the rectus muscles to the ribs and costochondral junctions, but is more typically an acquired condition with advancing age, obesity, or following pregnancy In the postpartum setting, rectus diastasis tends to occur in women of advanced maternal age, after multiple or twin pregnancies, or in women who deliver high-birthweight infants

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Surgical correction of a severe rectus diastasis by plication of the anterior rectus sheath may be undertaken for cosmetic indications, or if it is associated with disability of abdominal wall muscular function.

rectus sheath hematoma 

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terminal branches of the superior and inferior epigastric arteries course deep to the posterior aspect of the left and right rectus pillars and penetrate the posterior rectus sheath Injury to these vessels or to any of the network of collateralizing vessels within the rectus sheath and muscles can result in a rectus sheath hematoma Spontaneous rectus sheath hematomas have been described in the elderly and in those on anticoagulation therapy Patients frequently describe the sudden onset of unilateral abdominal pain that may be confused with lateralized peritoneal disorders such as appendicitis. Below the arcuate line, a hematoma may cross the midline and cause bilateral lower quadrant pain.

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The ability to appreciate an intra-abdominal mass is ordinarily degraded with contraction of the rectus muscles

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Fothergill's sign is a palpable abdominal mass that remains unchanged with contraction of the rectus muscles and is classically associated with rectus hematoma

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Umbilical hernias develop at the umbilical ring and may be present at birth or develop gradually during the life of the individual Umbilical hernias are present in approximately 10% of all newborns and are more common in premature infants Most congenital umbilical hernias close spontaneously by age 5 years. If closure does not occur by this time, elective surgical repair is usually advised Adults with small, asymptomatic umbilical hernias may be followed clinically

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Patients with advanced liver disease, ascites, and umbilical hernia require special consideration Enlargement of the umbilical ring usually occurs in this clinical situation as the result of increased intra-abdominal pressure from uncontrolled ascites The first line of therapy is aggressive medical correction of the ascites with diuretics, dietary management, and paracentesis for tense ascites with respiratory compromise These hernias usually are filled with ascitic fluid, but omentum or bowel may enter the defect after a large volume paracentesis Uncontrolled ascites may lead to skin breakdown on the protuberant hernia and eventual ascitic leak, which can predispose the patient to bacterial peritonitis Patients with refractory ascites may be candidates for transjugular intrahepatic portocaval shunting (TIPS), nonselective surgical portosystemic shunt, or liver transplantation Umbilical hernia repair is best performed after the ascites is controlled

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The greater omentum develops from the dorsal mesogastrium, which begins as a double-layered structure

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The gastrocolic ligament and the gastrosplenic ligament are those segments of the greater omental apron that connect the named structures

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In the adult, the greater omentum lies in between the anterior abdominal wall and the hollow viscera, and usually extends into the pelvis to the level of the symphysis pubis

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Lesser omentum, otherwise known as the hepatoduodenal and hepatogastric ligaments, develops from the mesoderm of the septum transversum, which connects the embryonic liver to the foregut The common bile duct, portal vein, and hepatic artery are located in the inferolateral margin of the lesser omentum, which also forms the anterior margin of the Foramen of Winslow. The blood supply to the greater omentum is derived from the right and left gastroepiploic arteries. The venous drainage parallels the arterial supply to a great extent with the left and right gastroepiploic veins ultimately draining into the portal system.

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Interruption of the blood supply to the omentum is a rare cause of an acute abdomen that may be secondary to torsion of the omentum around its vascular pedicle, thrombosis or vasculitis of the omental vessels, or omental venous outflow obstruction many cases will be indistinguishable from suppurative appendicitis, cholecystitis, or diverticulitis. In these instances, laparoscopy has provided a great advance, providing access to an accurate diagnosis as well as treatment. Resection of the infarcted tissue results in rapid resolution of symptoms

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Root of the small intestinal mesentery wall normally courses in an oblique direction, from the left upper quadrant at the ligament of Treitz to the right lower quadrant at the ileocecal valve and the fixed cecum

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Anatomic anomalies of the mesentery related to rotational disorders can lead to paraduodenal or mesocolic hernias, which can present as chronic or acute intestinal obstruction in children or adults

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Sclerosing mesenteritis, also referred to as mesenteric panniculitis or mesenteric lipodystrophy, is a rare chronic inflammatory and fibrotic process that involves a portion of the intestinal mesentery etiology of this process is unknown, but its cardinal features are a nonneoplastic mesenteric mass and varying relative quantities of fibrosis and chronic inflammation on histologic examination The mass may be up to 40 cm in diameter. Accordingly, patients typically present with symptoms of a mass lesion. Abdominal pain is the most frequent presenting symptom, followed by the presence of a nonpainful mass or intestinal obstruction

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Retroperitoneum defined as the space between the posterior envelopment of the peritoneum and the posterior body wall The retroperitoneal space is bounded:  

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superiorly by the diaphragm posteriorly by the spinal column and iliopsoas muscles inferiorly by the levator ani muscles

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Although technically bounded anteriorly by the posterior reflection of the peritoneum, the anterior border of the retroperitoneum is quite convoluted, extending into the spaces in between the mesenteries of the small and large intestine

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Because of the rigidity of the superior, posterior, and inferior boundaries, and the compliance of the anterior margin, retroperitoneal tumors tend to expand anteriorly toward the peritoneal cavity

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urinary    

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circulatory  

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aorta inferior vena cava

digestive  

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adrenal glands kidneys ureter bladder

esophagus (part) rectum

Reproductive 

uterus