Embryology

Meckel's Diverticulum

Outcome

Patients with biliary atresia experience jaundice, poor nutrition and rapidly declining liver function due to biliary cirrhosis. Currently, if the biliary tract is diverted before 3 months of age, one-third of these patients will survive without requiring transplant, while one-third will survive to require transplant in childhood and the remainder will die from liver failure.

For patients with EHPH, sclerotherapy is effective in the treatment of acute variceal bleeding in up to 75% of patients. However, several follow-up sessions are necessary to obliterate the varices and a rebleeding rate of 5-25% is expected. Persistent variceal bleeding as well as hypersplenism may require a TIPS or surgical shunt. Selective shunts have proven successful for the control of bleeding, thrombocytopenia and leukopenia, without creating great risk of encephalopathy.

For the most part, Meckel's diverticulum is clinically silent and is most often an incidental finding at laparotomy. The incidental finding of an asymptomatic Meckel's diverticulum shows no gender predilection, although this is not the case with symptomatic lesions. Presence of a Meckel's diverticulum and problems associated with it are known as the "disease of twos." Persistence of the diverticulum in the general population is 2%; it is 2 times more prevalent in males when symptoms exist. It is located 2 feet from the ileocecal valve, is 2 cm wide and 2 inches long. There are two common clinical presentations (bleeding and obstruction or diverticulitis) in children around the age of two. There are two common heterotopic tissues within the Meckel's diverticulum (gastric or pancreatic tissue), particularly in those that develop clinical problems.

By the third week of gestation, the midgut of the fetus is connected to the yolk sac via the vitelline duct. The vitelline duct progressively narrows during development until the third month of gestation, when it disappears along with resolution of umbilical herniation. Meckel's diverticula, as well as other omphalomesenteric defects, arise from incomplete regression of the omphalomesenteric (vitelline) duct. Which anomaly will be manifested is dependent upon the stage at which this regression is arrested (Fig. 4.1).

Figure 4.1 Diagram depicting possible complications associated with different omphalomesenteric remnants

A. Meckel's diverticulum;

B. Meckel's diverticulum with ulceration and hemorrhage.

C. The vitelline duct normally regresses between the 5th and 7th weeks of fetal life. When failed regression results in a fibrous band, the midgut may volvulate around it.

D. The fibrous band, which also produce abnormal peritoneal spaces through which an internal hernia may result.

E. The omphalointestinal fistula. If a patent connection persists between the intestine and the umbilicus, the entity is recognized as an omphalointestinal fistula.

F. Omphalomesenteric sinus and cyst.

Meckel's diverticula always occur on the antimesenteric border of the ileum. Approximately 75% will have the distal tip free in the abdomen; while 25% will be tethered to the anterior abdominal wall. When a persistent fibrous cord exists, the bowel is predisposed to intestinal volvulus leading to obstruction. Obliteration of the proximal and distal duct with patency of the mid portion leads to the formation of a vitelline duct cyst.

When the duct remains patent, a fistula exists between the ileum and umbilicus.

The blood supply to a Meckel's diverticulum is a remnant of the vitelline arteries, which in utero provided circulation to the yolk sac. The right vitelline artery becomes the superior mesenteric artery, while the left usually obliterates. In the case of Meckel's diverticula, the blood supply is from a persistent left vitelline artery and will arise from the ileal, ileocolic or mesenteric arteries.

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