A 21-year-old man has had abdominal pain for several weeks. A CBC shows WBC count 8810/microliter, Hgb 9.9 g/dL, Hct 28%, MCV 72 fL, and platelet count 272,000/microliter. A colonoscopy is performed after a stool specimen is positive for occult blood. No lesions are seen on colonoscopy. An upper GI endoscopy is likewise unremarkable. A radiographic small bowel series shows a 3 cm outpouching in the ileum.
What is the name for this lesion?
Meckel diverticulum. It is difficult to diagnose. Radiographic procedures, including barium studies, angiography, and nuclear medicine scans have been employed. Wireless capsule endoscopy may also be utilized. However, the sensitivity for detection is not 100%.
What is the embryologic origin?
The development of the embryonic midgut gives rise to the small intestine. During development, this midgut is connected to the yolk sac by the vitelline duct. A small portion of the vitelline duct may persist as a Meckel diverticulum, a small outpouching located in the ileum. A much rarer vitelline fistula connecting the gut to the abdominal wall skin at the umbilicus may occur.
Why was there blood loss in this case?
Another embryologic mistake is the presence of a tissue where it should not be. This is known as ectopia. The most common ectopic tissue in the bowel is pancreas. Small nodules of pancreatic tissue are generally less than 1 cm in size and these nodules mind their own business (they are asymptomatic). However, an occasional Meckel diverticulum may have ectopic gastric tissue. Since the small bowel mucosa is not equipped to deal with gastric acid secretion, it can ulcerate and bleed.
How common is this condition?
About 1 - 2% of persons have a Meckel diverticulum and only a few of these are symptomatic. Less than half may contain ectopic gastric mucosa.