Applied Radiology

CASE SUMMARY:

An 82-year-old woman presented with a 24-hour history of sharp, mid-abdominal pain radiating to the right lower quadrant. Physical examination revealed right lower quadrant tenderness with localized rebound and guarding. The patient was afebrile. Laboratory values demonstrated a normal white blood cell count and normal blood chemistry.

Plain abdominal radiographs showed a nonspecific bowel gas pattern without evidence of abnormal calcification or soft-tissue mass. A contrast-enhanced CT scan of the abdomen and pelvis was performed (figure 1), and a 2-cm thick-walled, fluid-filled mass was identified in the right mid-abdomen adherent to the wall of the distal ileum, associated with surrounding inflammatory changes. A radionuclide scan using 99-m Tc-pertechnetate was negative. The lesion subsequently was removed surgically (figure 2).

Diagnosis:

Inflamed Meckel's diverticulum

Discussion:

The gross pathologic specimen was a portion of ileum containing a purulent, inflamed diverticulum on the antimesenteric border with inflammation of the mesenteric fat. Microscopic examination demonstrated gastric metaplasia.

Meckel's diverticulum is the most frequent congenital anomaly involving the intestinal tract. The incidence at autopsy has been reported to be 0.3 to 3%.1 This is a true diverticulum because it contains all the layers of the bowel wall and, unlike pseudodiverticula, arises from the antimesenteric border. The diverticulum is formed by incomplete obliteration of the ileal end of the vitilline duct and usually is located within 100 cm of the ileocecal valve.1 Histologically, ectopic gastric mucosa is present in about 25% of all Meckel's diverticula, in over 50% of those that are symptomatic, and in 90% of those presenting with bleeding.2

Most Meckel's diverticula are clinically silent and become apparent only in patients with complications, which is reported to occur in 19% of cases.3 Intestinal obstruction is the most common complication; it may be caused by any of the following: strangulation of the bowel, intussusception, volvulus, incarceration of the diverticulum in a Littre's hernia, or tumors originating in the diverticulum.4 Another complication, bleeding, usually occurs in children, where it is the most common presenting sign. Diverticulitis occurs in 13 to 31% of the patients who have complications.5 This condition may mimic the symptoms of acute appendicitis. The inflammation usually results from the effect of peptic acids produced by ectopic gastric mucosa on the surrounding ileal mucosa.3 Other causes are similar to acute appendicitis, such as enteroliths obstructing the lumen.

It may be difficult to diagnose a Meckel's diverticulum unless it becomes inflamed, as in the case presented here. Radionuclide scanning with technetium pertechnetate detects ectopic gastric mucosa in Meckel's diverticula in approximately 80 to 90% of asymptomatic pediatric patients, but in less than 50% of adults.2 Small bowel series rarely provide the diagnosis, and computed tomography often is not helpful because it is difficult to differentiate a Meckel's diverticulum from a bowel loop in the abdomen on CT.6 However, due to the inflammation in this case, the Meckel's diverticulum was able to be distinguished from other small bowel loops, and was therefore able to be diagnosed on the CT scan.

In the appropriate clinical setting, an inflamed Meckel's diverticulum should be considered (along with the far more common acute appendicitis) in the differential diagnosis of acute right lower quadrant pain.

References

1. Gore RM, Levine MS, Laufer I: Textbook of Gastrointestinal Radiology, pp 1002-1004. Philadelphia, WB Saunders, 1994.

2. Putman CE, Ravin CE: Textbook of Diagnostic Imaging, ed 2, pp 782-783. Philadelphia, WB Saunders, 1994.

3. Rossi P, Gourtsoyiannis N, Bezzi M, et al: Meckel's diverticulum: imaging diagnosis. AJR 166:567-573, 1996.

4. Mackey WC, Dineen P: A fifty-year experience with Meckel's diverticulum. Surg Gynecol Obstet 156:56-64, 1983.

5. Yamaguchi M, Takeuchi S, Awazu S: Meckel's diverticulum: Investigation of 600 patients in Japanese literature. Am J Surg 136:247-249, 1978.

6. Ikard RW: Diagnosis of Meckel's diverticulum by computerized tomography. Tenn Med 89(5):164-165, 1996.

7. Nigogosyan M, Dolinskas C: CT demonstration of inflamed Meckel's diverticulum. J Comput Assist Tomogr 14(1):140-142, 1990.

Prepared by Lance J. Becker, MD and Karen Fried, MD, Lenox Hill Hospital,

New York, NY.