complication of a Meckel diverticulum is a bleeding ulcer, typically presenting as painless rectal bleeding Ectopic gastric mucosa in such patients is usually present in the diverticulum The acid secretion produces ulceration at the junction of the normal ileal mucosa with the ectopic mucosa Currant jelly stools or hemorrhage may be present Other modes of presentation include diverticulitis, perforation with peritonitis, or intussusception with the diverticulum serving as a lead point Enteral contrast studies usually fail to outline a Meckel diverticulum The imaging modality of choice for detection of ectopic gastric mucosa in a bleeding Meckel diverticulum is nuclear scintigraphy A well-defined focal accumulation of radionuclide (99m-technetium pertechnetate) usually appears at or about the same time as activity in the stomach and gradually increases in intensity ( Fig 116.19 ) A duplication cyst with gastric mucosa shows the same focal accumulation of radionuclide Preoperative differentiation between two lesions as a cause of GI bleeding is not important The accuracy of scintigraphy in detection of ectopic gastric mucosa in Meckel diverticula is approximately 95% Falsenegative results may rarely occur in patients with rapidly bleeding Meckel diverticula and with those diverticula that not contain gastric mucosa In any child with a major rectal bleed and a negative scan, further workup is required, including an arteriogram if the bleeding continues to be active or colonoscopy when the bleeding is not active