Meckel’s diverticulum is a pouch of extra tissue in the wall of the small intestine. It's the most common birth defect of the gastrointestinal tract.

In most people, Meckel's diverticulum doesn't cause problems or require treatment. One serious complication, called Meckel's diverticulitis, is an infection and inflammation of the pouch. Meckel's diverticulitis requires prompt medical attention.

Meckel’s Diverticulum
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Meckel's diverticulum develops before birth. It is created by a section of tissue that acts as a link to the umbilical cord in early development. Normally this tissue shrinks and is reabsorbed by the 7th week of pregnancy. In Meckel's diverticulum, the tissue remains, creating a pouch or bulge in the lower part of the small intestine.

It is not clear why this tissue is not reabsorbed, but it may be caused by a combination of genetic and environmental factors.