Meckel's diverticulum

 This is the most common congenital anomaly of the gastrointestinal tract and occurs in 0.3-3% of people, but the vast majority of affected individuals are asymptomatic throughout life. The diverticulum results from failure of closure of the vitelline duct, with persistence of a blind-ending sac arising from the anti-mesenteric border of the ileum; it usually occurs within 100 cm of the ileocaecal valve and is up to 5 cm long. Approximately 50% contain ectopic gastric mucosa; rarely, colonic, pancreatic or endometrial tissue is present. Complications most commonly occur in the first 2 years of life but are occasionally seen in young adults. Bleeding can result from ulceration of ileal mucosa adjacent to the ectopic parietal cells and presents as recurrent malaena or altered blood per rectum. The diagnosis can be made by scanning the abdomen using a gamma counter following an intravenous injection of 99mTc-pertechnetate, which is concentrated by ectopic parietal cells. Other complications include intestinal obstruction, diverticulitis, intussusception and perforation. Intervention is unnecessary unless complications occur.