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Colon, Diverticulitis: Imaging
Updated: Aug 24, 2009
Radiography
Single-contrast barium enema study demonstrates mild sigmoid diverticulitis with thickening of the mucosal folds and luminal narrowing.
Single-contrast barium enema study in a patient with diverticulitis demonstrates tethering of the sigmoid colon as a result of a diverticular abscess.
Single-contrast barium enema study in a patient with diverticulitis demonstrates an intramural abscess filling with barium.
Findings
Plain radiography
Plain radiographs usually do not show any findings in uncomplicated diverticulitis, but a left-sided pelvic mass, localized ileus, or partial bowel obstruction may be seen occasionally. Pneumoperitoneum, portal venous gas, and extraluminal air-fluid levels may be noted in patients with complicated diverticulitis.
Barium study
Prior to the advent of abdominal CT scanning, barium enema evaluation was the examination of choice for the diagnosis of diverticulitis. A single-contrast examination is the preferred method in patients in whom diverticulitis is suspected.
The appearance of diverticula varies with the projection in which they are viewed and with the amount of air and barium they contain. In profile, a diverticulum appears as a protrusion outside of the colon that is joined to the colonic wall by a neck. En face, a diverticulum may appear as a well-defined collection of barium or as a ring shadow. It may resemble a bowler hat.
On barium enema examination, diverticulitis can be diagnosed by recognizing a perforated diverticulum. Barium may track through a perforated diverticulum into a sinus tract, fistula, or abscess. Less commonly, it may extravasate freely into the peritoneum. A diverticular abscess may cause extrinsic compression of the colonic lumen. Initially, this compression occurs on the mesenteric side of the colon, but it may spread to encircle the lumen.
Many other features of diverticulitis are depicted on barium enema images. Narrowing, deformity, or displacement of the bowel lumen is commonly seen. The colon may have an abnormal mucosal pattern. A soft-tissue mass may be seen, and this mass may contain gas or air-fluid levels. Extraluminal tracts filled with barium may end blindly as sinus tracts or may connect with an adjacent organ as a fistula, most commonly to the bladder or bowel. Fistulas also may involve the vagina, ureter, hip, and soft tissues of the thigh. Occasionally, plain radiographs demonstrate colovesical fistulas with the presence of air in the bladder. Additional manifestations of diverticulitis include localized ileus and intestinal obstruction.
Fistula formation to the anterior abdominal wall can be evaluated by using a fistulogram.
Degree of Confidence
Stefansson et al reported a sensitivity of 82% and a specificity of 81% in using barium enema in a group of 88 patients in whom diverticulitis was suspected.10
False Positives/Negatives
The primary disadvantage of barium enema examination in the evaluation of diverticulitis is its limited ability in cases of extraluminal disease. Abscesses that do not communicate with the colon may not be detected. Although communication with the urinary bladder may be demonstrated, only 20% of colovesical fistulas are revealed on barium enema evaluation. Alternative conditions, such as appendicitis, epiploic appendagitis, gynecologic pathology, and renal colic, may not be depicted.
Although barium enema evaluation is excellent for differentiating diverticulitis from colon carcinoma, this differentiation is occasionally difficult. In diverticulitis, the diverticula usually are seen along with a gradual zone of transition and preservation of the mucosal folds. In carcinoma, a much sharper zone of transition is seen, with destruction of the mucosal folds. However, because diverticulosis is common, diverticula often are seen in patients with colon carcinoma. If the lesion completely obstructs the passage of contrast material during the barium enema test, the differentiation of diverticulitis from carcinoma is usually not possible.
Computed Tomography
CT scan demonstrates mild diverticulitis of the descending colon, with wall thickening, a diverticulum, and mild stranding of the pericolic fat.
CT scan demonstrates typical sigmoid diverticulitis with wall thickening, diverticulosis, and stranding at the root of the sigmoid mesentery (same patient as in Image 3).
CT scan demonstrates typical sigmoid diverticulitis with wall thickening, diverticulosis, and stranding at the root of the sigmoid mesentery (same patient as in Image 2).
CT scan in a patient with diverticulitis demonstrates an abscess adjacent to the sigmoid colon.
CT scan demonstrates diverticulosis in a patient with colon carcinoma. Although the mass is somewhat eccentric, this type of case is difficult to differentiate from diverticulitis, and follow-up imaging is often necessary.
The CT image demonstrates a pericolic fat-attenuation mass with surrounding infiltration of the fat, which is characteristic of epiploic appendagitis.
Findings
Techniques for the CT evaluation of diverticulitis vary from institution to institution. At the authors' institution, oral contrast material is administered to opacify the small bowel. The oral contrast agent usually does not reach the sigmoid colon, but colonic opacification usually is not necessary for the evaluation of diverticulitis.11 Occasionally, the rectal administration of contrast material may help in difficult cases.
CT with rectal contrast enhancement or CT cystography may help in diagnosing fistulas. At the authors' institution, the intravenous contrast material is administered routinely, although it usually is not essential for diagnosis. Intravenous contrast material may help in revealing diverticular abscesses and fistulas and in demonstrating the enhancement pattern of the colonic wall. However, it is probably more helpful in the diagnosis of alternative diseases that may mimic diverticulitis.12
- Diverticula are identified on CT scans as outpouchings of the colonic wall. They may contain air, barium, or fecal material.
- The diagnosis of diverticulitis by using CT scans is based on the detection of colonic and paracolic inflammation in the presence of underlying diverticula.13
- Linear stranding in the fat of the root of the sigmoid mesentery is a common finding in patients with diverticulitis.
- The appearance of diverticulitis may vary from minimal stranding of the mesenteric fat and small extraluminal collections of fluid or air in mild cases to extensive stranding and increased attenuation of the fat along with fistulas or large abscesses in more severe cases.
- Symmetric thickening of the colonic wall of approximately 4-5 mm is common.
- With distension, the luminal diameter of the involved segments usually measures less than 1 cm.
- Enhancement of the colonic wall is commonly noted. This usually has inner and outer high-attenuation layers, with a thick middle layer of low attenuation.
- Small fluid collections in the colon wall may be present; they represent intramural abscesses.
- Free diverticular perforation results in the extravasation of air and fluid into the pelvis and peritoneal cavity.
- Peritoneal fluid containing air bubbles may be seen, often adjacent to the sigmoid colon. These findings indicate peritonitis caused by free perforation of a diverticulum.
- On CT scans, fistulas and sinus tracts appear as linear or branching structures in the pericolic fat.
- Fistulas may communicate with an abscess or another hollow viscus, most commonly the bladder.
- Air in the bladder in the presence of a nearby segment of diverticulitis is suggestive of a colovesical fistula. If a colovesical fistula is suspected, the administration of rectal contrast material may be helpful. In this case, intravenous contrast agent should not be used so that the presence of contrast enhancement in the bladder can allow definitive diagnosis of a fistulous connection. Alternatively, a CT cystogram may be obtained with the intravesical administration of contrast material via a Foley catheter without the use of an oral or rectal contrast agent.
- Rao et al described an arrowhead-shaped collection of contrast medium between thickened folds as a specific sign of diverticulitis in regions other than the cecum.14 However, this finding was noted only in approximately one quarter of patients. The study was performed by using rectal contrast enhancement. The arrowhead sign is caused by contiguous spread of inflammation from the diverticulum to the colonic wall, resulting in a triangular space between the thickened colonic folds. This sign is seen more commonly with rectal contrast material than with oral contrast material. In the cecum, another arrowhead sign has been described as being specific for appendicitis.
- Other nonspecific CT findings in diverticulitis include collections of fluid at the root of the mesocolon and engorgement of mesocolic vessels.
Degree of Confidence
Cho demonstrated that CT has a sensitivity of 93% for the diagnosis of diverticulitis, which is higher than the 80% sensitivity of barium enema studies.15 Often, CT is the only radiologic test needed to establish the diagnosis and to direct medical or surgical therapy or radiologic intervention.
False Positives/Negatives
False-negative CT scans result from the difficulty in detecting early-stage diverticulitis with only minor changes in the pericolic fat.
Increased attenuation in the pericolic fat is not specific for diverticulitis, and false-positive findings occur. The differential diagnosis includes neoplasm, inflammatory bowel disease, appendicitis, and epiploic appendagitis. The presence of fluid in the root of the mesentery and the engorgement of adjacent sigmoid mesenteric vasculature suggest an inflammatory process, and the absence of stranding of the pericolic fat is typical of carcinoma.
Eccentric colonic wall thickening or marked concentric wall thickening is suggestive of colon carcinoma. The wall in carcinoma is frequently thicker than 2 cm, whereas it is usually thinner than 1 cm in cases of diverticulitis. Although most cases of diverticulitis involve a segment of less than 10 cm, involvement of a segment greater than 10 cm is specific for diverticulitis. As with barium enema results, findings of overhanging edges or shoulder formation with a rigid lumen are typical of a carcinoma.
The presence of pericolic lymph nodes also suggests colon cancer rather than diverticulitis.16 In addition, a layered pattern of enhancement of the colonic wall is typical of an inflammatory process, such as diverticulitis, and it is not usually seen in carcinomas. However, in some patients, distinguishing diverticulitis from colon cancer by using CT alone may not be possible, and follow-up examination after resolution of the acute episode may be necessary. Biopsy may also be required.
The presence of diverticula in the involved segment is helpful in distinguishing diverticulitis from other inflammatory conditions of the colon. Epiploic appendagitis may result from torsion of an epiploic appendage or thrombosis of an appendageal vein, and patients present with localized abdominal pain with a sudden onset. CT scans typically demonstrate an ovoid fat-attenuation mass with surrounding stranding. The colonic wall usually is not thickened. These findings help differentiate epiploic appendagitis from diverticulitis.
Ultrasonography
Findings
Ultrasonography in patients with diverticulitis is performed transabdominally with a 2- to 4-MHz convex-array transducer and compression.17,18,19
In diverticulitis, ultrasonographic findings include thickening of the bowel wall by more than 4 mm. Inflamed diverticula appear as round or ovoid highly echogenic structures with a ring-down artifact. Inflammation of the pericolic fat is revealed as an area of increased echogenicity adjacent to the colonic wall. Abscess formation appears as a well-defined hypoechoic mass near the colon, and it may demonstrate shadowing because of the presence of air. The absence of peristalsis is helpful for differentiating abscess from adjacent loops of bowel. Intramural sinus tracts appear as linear echogenic foci, often with ring-down artifacts. In addition, the patient may experience pain with compression of the affected region.
Degree of Confidence
According to Pradel et al, the sensitivity of sonography is 85%, and its specificity is 84% in the diagnosis of diverticulitis.20 These are similar to the results of CT. However, ultrasonography is operator dependent, and technologists at most centers in the United States have little experience with its use in the evaluation of diverticulitis. Sonography may be totally unsuccessful, and sonograms may not show the colon in obese patients or in those with bowel gas.
False Positives/Negatives
False-positive findings result from the presence of neoplasms, inflammatory or ischemic colonic diseases, or adjacent extracolonic inflammatory conditions.
Nuclear Imaging
Findings
Scanning with technetium 99m – labeled red blood cells often is performed to locate the site of active gastrointestinal tract bleeding, and it may be helpful in evaluating the bleeding due to diverticulosis. Nuclear medicine studies have a limited role in the evaluation of diverticulitis.
Angiography
Findings
Approximately one half of all cases of lower gastrointestinal hemorrhage are caused by colonic diverticulosis. Although most diverticula occur in the left side of the colon, diverticular hemorrhage usually originates from the right side. Angiography may demonstrate diverticular hemorrhage as puddling or staining that persists beyond the capillary and venous phases. Embolization or the intra-arterial infusion of vasopressin may be used to treat gastrointestinal bleeding.
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References
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Kori T, Nemoto M, Maeda M, et al. Sonographic features of acute colonic diverticulitis: the "dome sign". J Clin Ultrasound. Sep 2000;28(7):340-6. [Medline].
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Further Reading
Related eMedicine topics
Diverticular Disease (Emergency Medicine)
Diverticulitis (Gastroenterology)
Clinical guidelines
Practice parameters for sigmoid diverticulitis
Surgical treatment of diverticulitis
ACR Appropriateness Criteria® left lower quadrant pain
ACR Appropriateness Criteria® acute abdominal pain and fever or suspected abdominal abscess
Clinical trials
Study to Evaluate the Duration of Treatment With Ertapenem in Acute Attacks of Sigmoid Diverticulitis.
Prevention of Recurrence of Diverticulitis
Keywords
diverticulitis, diverticulum, diverticulosis, diverticular disease, diverticular disease of the colon, outpouching, diverticula, colonic diverticula, intestinal disease, diverticular hemorrhage, bowel obstruction, gastrointestinal hemorrhage, GI tract hemorrhage
