CT

DR SAKHER-ALKHADERICONSULTANT RADIOLOGIST AMC

IMAGING OF ACUTE DIVERTICULITIS

Diverticulosis Is the condition of having diverticula in the colon, which are outpocketings of the colonic mucosa and submucosa through weaknesses of muscle layers in the colon wall. It is highly prevalent in western countries. These are more common in the sigmoid colon, which is a common place for increased pressure.

Diverticulitis Is a complication of diverticulosis,

Diverticulitis is the result of obstruction of the neck of the diverticulum, with subsequent inflammation, perforation and infection.  Initially inflammation and infection are contained by inflammatory phlegmon. The infection may later progress to abscess formation and/or generalised peritonitis.

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 occasionally be seen. 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.

Double contrast barium enema study showing multiple colonic diverticulosis

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.

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.

Single-contrast barium enema study demonstrates sigmoid diverticulitis with an intramural sinus tract. Fistula formation in the small bowel is noted.

Single-contrast barium enema study demonstrates mild sigmoid diverticulitis with thickening of the mucosal folds and luminal narrowing.

Single-contrast barium enema study demonstrates sigmoid diverticulitis with fistula formation in the vagina.

UltrasonographyUltrasonography in patients with diverticulitis is performed transabdominally with a 2- to 4-MHz convex-array transducer and compression.In diverticulitis, ultrasonographic findings include thickening of the bowel wall by more than 4 mm. Inflamed diverticula appear as round or ovoid, hypoechogenic 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.

Sonographic features of uncomplicated diverticulosis. diverticula appear as bright “ear” out of the bowel wall (a); a central shadowing echogenicity may indicate the presence of fecalith (b).

Diverticulitis with a hypoechoic diverticulum with peridiverticulitis with hyperechoic inflamed mesenteric fat and a small effusion

Inflamed diverticulum and abscess

Peridiverticulitis and abscess CT and US

Diverticulitis with perforation to the abdominal wall

Computed Tomography CT is the modality of choice for the diagnosis and staging of

diverticulitis. Appearances include: -Pericolic stranding, often disproportionately prominent compared to the amount of bowel wall thickening 3

-Segmental thickening of the bowel wall-Enhancement of the colonic wall 

usually has inner and outer high-attenuation layers, with a thick middle layer of low attenuation

-Diverticular perforation extravasation of air and fluid into the pelvis and peritoneal cavity

-Abscess formation (seen in up to 30% of cases)may contain fluid, gas or both

-Fistula formationgas in the bladderdirect visualisation of a fistulous tract

Hinchey classification of acute diverticulitis

stage 1a - phlegmonstage 1b - diverticulitis with pericolic or mesenteric abscessstage 2 - diverticulitis with walled off pelvic abscessstage 3 - diverticulitis with generalised purulent peritonitisstage 4 - diverticulitis with generalised faecal peritonitis

Complications

Recognised complications include: -abscess formation-fistula formation

bladder: colovesical fistulavagina: colovaginal fistulabowel: coloenteric fistula or colocolic fistulaskin: colocutaneous fistula

-small bowel obstructions from adhesions-perforation resulting in pneumoperitoneum

Areas of inflammation and fat stranding surrounds the sigmoid colon , findings are characteristic of diverticultis

Diverticulitis, severe colovesical fistula

CT scan demonstrates mild diverticulitis of the descending colon, with wall thickening, a diverticulum, and mild stranding of the pericolic fat.

CT scan in a patient with diverticulitis demonstrates an abscess adjacent to the sigmoid colon.

Colonic diverticulosis , no diverticultis

 Diverticula (arrowheads) and inflammation around the sigmoid colon, indicating diverticulitis. A small, adjacent, early abscess (open arrow) is noted.

CT scan of perforated diverticulitis with diverticula (thin arrows) and free abdominal air (thick arrows).

MAGNETIC RESONANCE IMAGING

Magnetic resonance imaging (MRI) can effectively diagnose acute diverticulitis, with reported sensitivity of 86 to 94% and specificity of 88 to 92%.It is likely that continually improving MRI techniques may result in higher sensitivity and specificity in the future. Buckley et al described MRI findings in patients with acute colonic diverticulitis, identifying findings similar to CT: bowel wall thickening, pericolic stranding, presence of diverticula, and complications . MRI is also comparable with CT in its ability to identify alternative diagnoses. Similar to ultrasound, MRI has the benefit of no radiation exposure, but because it is operator independent, it may be more applicable as the test of choice as the medical community becomes more aware of the risks of radiation exposure and seeks alternative imaging modalities to CT. 

Magnetic resonance image (MRI) of right-sided diverticulitis. Axial MRI of a 30-year-old woman with right abdominal pain . T2-weighted MRI shows ascending colonic wall thickening with fat stranding around inflamed diverticulum (arrow).

THE END