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Original Report |
1 All authors: Department of Abdominal Radiology, Tisch Hospital, New York University Medical Center, 560 First Ave., New York, NY 10016.
Received July 25, 2003;
accepted after revision September 23, 2003.
Address correspondence to G. L. Bennett
(genevieve.bennett{at}med.nyu.edu).
Abstract
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CONCLUSION. The inflamed Meckel's diverticulum may be visualized on CT in most patients, appearing as a blind-ending pouch of variable size and mural thickness and containing fluid, air, or particulate material with surrounding mesenteric inflammation. The location of the diverticulum may vary from the right lower quadrant to the mid abdomen, with most cases in this series located near midline. Optimal luminal opacification of the ileocecal bowel with oral contrast material facilitated detection of the diverticulum and also proved invaluable in enabling identification of the normal appendix. The diagnosis is most difficult in the setting of secondary intestinal obstruction.
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CT examinations were performed on helical CT scanners (CTi or HiSpeed Advantage, General Electric Medical Systems, Milwaukee, WI). CT parameters included slice collimation, 5–7 mm; helical pitch, 1.0–1.4; 120 kVp; 210–260 mA; and table speed, 7–10 mm/sec. Contrast material was administered at a rate of 2–3 mL/sec via calibrated EnVision CT injectors (Medrad, Pittsburgh, PA) using 1.0- to 1.25-inch-long (2.5–3.1 cm) 20- or 22-gauge plastic venous cannulas inserted into an antecubital vein. Patients received 125–150 mL of either ionic (Conray 60 [iothalamate meglumine], Mallinckrodt Medical, St. Louis, MO) or nonionic (Ultravist [iopromide] 300 mg I/mL, Berlex Laboratories, Wayne, NJ) contrast medium on the basis of institutional guidelines for contrast media selection similar to those proposed by the American College of Radiology. All patients received approximately 750 mL of dilute 2% water-soluble iodinated oral contrast material (Gastrografin [meglumine diatrizoate], Bristol-Myers Squibb, Wallingford, CT) to opacify the gastrointestinal tract before data acquisition.
The hard-copy images of the 11 CT studies were retrospectively reviewed in consensus by three experienced abdominal radiologists. Studies were evaluated for the following findings: visualization, location, size, mural thickness, and content of the diverticulum. Associated findings that were also evaluated included the presence or absence of mesenteric inflammation, fluid, or lymphadenopathy; intestinal obstruction; and the identification of a normal appendix. Radiology reports were reviewed to determine the patient's presenting complaint and the prospective preoperative diagnosis offered at the time of initial CT interpretation.
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On retrospective review, Meckel's diverticulum was definitively identified in nine of the 11 patients. In the two patients in whom the diverticulum was not visualized, there was evidence of small-bowel obstruction with no oral contrast material opacification of distal small-bowel loops.
Of the nine diverticula identified, the diverticulum was located at midline in four patients (Fig. 1A, 1B, 1C), slightly to the right of midline in one, and to the left of midline in one. In one of these patients, a direct communication was shown between the diverticulum and the umbilicus (Fig. 2A, 2B). The diverticulum was located in the right lower quadrant in two patients (Fig. 3A, 3B) and in the right paracolic gutter, anterior to the ascending colon, in one patient (Fig. 4A, 4B). The diverticulum was located inferior to the level of the terminal ileum in four patients and superior to the terminal ileum in five patients. Oral contrast material was not present in any of the visualized diverticula. The diverticulum contained fluid and air in five patients; fluid, air, and particulate material in three patients; and fluid only in one patient. No enteroliths were visualized. Mural thickness of the diverticulum ranged from 1 to 18 mm (mean, 3.9 mm). In short-axis dimension, the diverticula ranged from 1.5 to 6 cm (mean, 2.5 cm) and in long axis from 2 to 7 cm (mean, 3.3 cm). The wall of the diverticulum showed mural enhancement comparable with that of adjacent small bowel in all patients except one. This patient had histopathologic evidence of a gangrenous Meckel's diverticulum (Fig. 5A, 5B).
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Mild inflammatory changes were present in the adjacent mesentery in all patients with visualized diverticula, and in seven patients a small amount of mesenteric fluid was present. Small mesenteric lymph nodes measuring less than 1 cm in short-axis dimension were visualized in three patients (Fig. 1A, 1B, 1C). In addition to the two patients with small-bowel obstruction in which a diverticulum was not visualized, three additional patients had CT evidence of partial or complete small-bowel obstruction. A normal appendix was visualized in seven patients, thus excluding the diagnosis of acute appendicitis (Fig. 3A, 3B). In one patient, only the proximal appendix could be visualized, and the erroneous diagnosis of tip appendicitis was made prospectively.
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The total lifetime complication rate of a Meckel's diverticulum is approximately 4% [7]. Symptomatic complications include bleeding, obstruction, or inflammation. The 2% incidence of this congenital abnormality combined with the 4% complication rate suggests that although uncommon, complications related to a Meckel's diverticulum will be encountered in clinical practice. Hemorrhage, which occurs in the presence of ectopic gastric glandular tissue, occurs as a result of ulceration of the diverticulum and adjacent ileum and generally presents in the pediatric population under the age of 2 years [1, 7]. Intestinal obstruction and diverticulitis are the main complications seen in adults, occurring in 40% and 20% of patients, respectively [8, 9].
A number of mechanisms can lead to inflammation of a Meckel's diverticulum causing diverticulitis [8]. Obstruction of the diverticular orifice with resultant stasis and bacterial infection can occur in a manner analogous to acute appendicitis and can occur as a result of an enterolith or foreign body. Alternatively, peptic ulceration of ileal mucosa related to ectopic gastric mucosa can be present. Diverticulitis may also result from diverticular torsion that causes secondary ischemia and inflammatory change. The clinical presentation, physical examination, and laboratory findings are typically nonspecific. Meckel's diverticulitis may be clinically indistinguishable from a variety of other intraabdominal inflammatory processes such as acute appendicitis, inflammatory bowel disease, or other causes of small-bowel obstruction. In one series, appendicitis was the most common preoperative diagnosis [10]. Fewer than 10% of patients are correctly diagnosed preoperatively [9].
Many imaging techniques have proven useful in identifying Meckel's diverticulum in symptomatic individuals [5]. These include a nuclear medicine pertechnetate scan, which yields positive results only in the presence of ectopic gastric mucosa and has an overall diagnostic accuracy of 90% in these patients. This test is most useful in children and has a positive predictive value of only 60% in the adult population. A Meckel's diverticulum may be shown at small-bowel follow-through examination; however, sensitivity for visualizing the diverticulum is increased by performing enteroclysis. Recently, sonographic findings of Meckel's diverticulitis in children have been described [11]. Arteriography is usually reserved for patients with acute hemorrhage or unexplained gastrointestinal bleeding.
A few case reports exist in the radiology literature that describe the CT findings of Meckel's diverticulitis [3–6]. We believe that this study is the first to describe CT findings of Meckel's diverticulitis in a larger series of patients. In our series, the CT appearance of the inflamed diverticulum varied considerably. The diverticulum appeared as a blind-ending pouch that generally contained fluid and air or particulate material. No oral contrast material was present within the lumen of the visualized diverticula, which ranged up to 7 cm in maximum length. All diverticula showed mural enhancement except for a single case complicated by severe ischemia, which was gangrenous at pathology. There were no enteroliths observed in our series either on CT or at pathology.
Five patients had associated small-bowel obstruction, two with high-grade and three with low-grade obstruction. Meckel's diverticulum may cause intestinal obstruction by several mechanisms [8]. The diverticulum itself may serve as a fulcrum for twisting of the adjacent small bowel with resultant obstruction. This situation is thought to be more likely when a residual fibrous band is present that connects the diverticulum to the mesentery or anterior abdominal wall. The diverticulum may also invaginate and serve as a lead point for intussusception or become incarcerated in a hernia. If the Meckel's diverticulum is inflamed, as was the case in our series, associated inflammation of the small bowel, inflammatory adhesions, or cicatricial luminal narrowing may lead to obstruction.
Patients who present with Meckel's diverticulitis are most often clinically suspected of having acute appendicitis. Appendicitis can be easily differentiated from an inflamed Meckel's diverticulum if a normal appendix is visualized on CT. The majority (67%) of Meckel's diverticula visualized in our study were located at or near midline and not in the right lower quadrant. The CT visualization of a diverticular attachment to the umbilicus is a helpful diagnostic sign that has been previously described [4]. This finding was observed in one patient in our series. The differential diagnosis of this finding may include an infected urachal duct cyst. The urachus is a vestigial structure that lies within the umbilical ligament at midline. On CT, an infected urachal duct cyst may also appear as a fluid-filled structure at midline with a thickened enhancing wall [12]. Unlike a Meckel's diverticulum, however, a urachal duct cyst will generally be intimately related to the dome of the bladder.
Differentiation of Meckel's diverticulitis from acute appendicitis is more difficult if the Meckel's diverticulum is located in the right lower quadrant or if a normal appendix is not visualized. Also, secondary inflammation of the appendix may be present, as was noted in one patient in our series. This study shows the importance of luminal opacification of the ileocecal bowel with oral contrast material for identifying both the diverticulum and a normal appendix. Appendiceal CT protocols that use only retrograde colonic opacification may be limited in this regard because such protocols may fail to opacify the ileum with enteric contrast material. Antegrade administration of oral contrast material may not result in ileal opacification in the setting of high-grade small-bowel obstruction. This occurred in two patients in our series in whom a Meckel's diverticulum was not retrospectively identified.
An additional rare cause of inflammation in the right lower quadrant, which could be considered in the differential diagnosis of Meckel's diverticulitis, is ileal diverticulitis. On CT, this condition may appear as an inflammatory process centered about the terminal ileum, with normal-appearing appendix and cecum. Diverticula may be visualized along the mesenteric border of the ileum in the area of inflammation, which helps to suggest the diagnosis. This diagnosis can be confirmed with a small-bowel series [13]. Crohn's disease is a more common cause of right lower quadrant inflammation. However, in addition to the absence of a diverticulum, Crohn's disease may exhibit other features not seen with Meckel's diverticulitis, such as mesenteric fibrofatty proliferation, fistula formation, and colonic involvement.
In conclusion, Meckel's diverticulitis should be considered in the differential diagnosis of acute abdominal pain in both pediatric and adult patients. If an inflammatory process is visualized on CT in the lower abdomen or pelvis, particularly at midline, or if there is evidence of distal small-bowel obstruction, one should carefully search for the presence of an inflamed diverticulum. If a normal appendix is identified, the likelihood of this diagnosis increases. Luminal opacification of the small bowel with oral contrast material facilitates the identification of the diverticulum. Similar to an inflamed appendix, the inflamed diverticulum typically shows mural contrast enhancement unless gangrenous changes have occurred. Administration of both IV and oral contrast material may help establish the diagnosis of Meckel's diverticulitis and should be administered whenever possible in patients undergoing CT evaluation of abdominal pain.
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