Radiology quiz

EUGENE C. ANANDAPPA, MD

aFall 1998

HISTORY: A 19-month-old white male with a 2 ½ month history of severe intermittent abdominal pain was admitted to rule out intussusception. Two and one half weeks ago he was admitted to another institution with a similar complaint. His hemoglobin was 3.3 g/dL, and he was transfused. He was then discharged with a diagnosis of "viral illness." Approximately two weeks prior to his admission to Children's, the parents noticed blood clots in the diaper. The stools were also dark because he was on iron. A barium enema showed possible malrotation and no intussusception, and the upper G.I. examination was normal. A 99mTc-O4- (sodium pertechnetate) scintigram was then performed.

QUESTION: What is the diagnosis ?

DIAGNOSIS: Meckel's diverticulum

Discussion

Meckel's diverticulum, which has an incidence of about 2 percent, is the most frequent congenital anomaly of the GI tract. The frequency is three times greater in males than in females. It is a noninherited "true" congenital diverticulum, the walls being composed of all the layers—mucosal, muscular and serosal—which is characteristic of the GI tract. It is usually located 60 to 90 cm proximal to the ileo-cecal valve and always attached to the antemesenteric side of the ileal wall. The size varies from 1 to 10 cm, although much larger diverticula have been described. The mucosal lining corresponds to that of the ileum, but it contains, in many instances, islands of heterotopic gastric, duodenal, jejunal or colonic mucosa or pancreatic tissue. Gastric mucosa is present in approximately 50 percent of cases.

From left to right (above): Anterior at 3 minutes. Anterior at 30 minutes. Right Lateral

Embryologically it is the proximal, i.e., the intestinal end of the vitelline or omphalomesenteric duct connecting the yolk sac to the primitive gut. This is normally obliterated at about the seventh week of fetal life. Failure of the vitelline duct to disappear in its entirety can result in a variety of remnants, i.e., conditions ranging from umbilico-intestinal fistula, umbilical sinus, omphalo-mesenteric cyst or a fibrous cord. In a Meckel's diverticulum, the proximal end remains patent, and in the course of fetal development develops into an appendage of the ileum.

Meckel's diverticulum is the most common cause of lower GI bleeding in previously healthy infants. More than 50 percent of infants with Meckel's have symptoms before the second year of life. The most common symptom of Meckel's divertivulum is rectal bleeding, with or without associated abdominal symptoms. The bleeding results from mucosal ulceration in the diverticulum or adjacent ileum caused by acid secreted by the ectopic gastric mucosa.

Imaging: The test is based on the accumulation of 99mTc-O4- in the surface epithelial cells of the gastric mucosa and then its secretion into the bowel lumen. Similarly, tissue having ectopic gastric mucosa such as Meckel's diverticulum or Barrett's esophagus concentrates and secretes the pertechnetate ion. A variety of drugs affect the gastric uptake of pertechnetate. Pentagastrin increases gastric uptake; Cimetidine increases its accumulation by inhibiting the release of pertechnetate from the cells. Perchlorate suppresses uptake by the gastric mucosa.

To perform the test, the patient should be NPO for two to four hours to reduce gastric motility. The GI tract should be free of barium. We do not routinely use pentagastrin or Cimetidine.

Following intravenous administration of pertechnetate, in a dose of 1 to 10 mCi (0.10 mCi per kg of body weight), radionuclide angiogram is obtained for 60 seconds followed by one-minute images for 30 to 60 minutes. A lateral image is useful to exclude activity in the GU tract.

The study above shows a three-minute and a 30-minute AP and lateral images. At three minutes, there is activity in the wall of the stomach; in addition there is another well-defined area of 99mTc-O4- localization in the right lower quadrant that appears about the same time as in the stomach and increases in intensity as the study progresses, as seen in the 30-minute images. On rare occasions, activity in the lesion fluctuates if active hemorrhage or intestinal secretions carry the 99mTc-O4- from the diverticulum. In questionable cases, a repeat study should be performed on another day with cimetidine. Other conditions in the abdomen also may cause the accumulation of 99mTc-O4-, including duplications, inflammation, intussusception, hemangioma and vascular malformations, bleeding ulcers, and some tumors.

The accuracy of 99mTc-O4- scintigram for Meckel's diverticulum is 90 percent. Prior to 99mTc-O4-scintigraphy, the lesion was diagnosed at surgery in about 60 percent of symptomatic patients. A normal study does not rule out the presence of a Meckel's diverticulum, because ectopic gastric mucosa must be present and functioning in order for the scintigram to be positive. Decreased function such as in infants, necrosis, or fibrosis may prevent localization and result in a negative scan.

FOR FURTHER READING

Treves ST: Pediatric Nuclear Medicine, New York:Springer-Verlag & Co. 1995.

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