CT colonography and anatomical features
Today, CT colonography (CTC) is actively used by surgeons as a "roadmap" for surgical planning. It successfully replaces traditional double-contrast barium enema.
When performing 3D endoluminal reconstruction, the digital cleansing function is used, which removes high-density contrast from fecal masses. However, it is important to remember false-positive results: a dense diverticulum (with a fecolith or inflammation) on the 3D model may look like a polyp. For differential diagnosis, 2D slices must be evaluated—they clearly show the fecolith, which often contains small gas bubbles.
- Diverticula of the right colon typically have wider necks.
- Small intramural outpouchings may be identified along the antimesenteric border.
Acute diverticulitis
Diverticulitis is the most common complication of the disease. It is based on the retention of fecal matter inside the outpouching, which leads to ischemic necrosis of the wall, microperforation, and the formation of a pericolic abscess in the surrounding adipose tissue.
CT is the gold standard for assessing the severity of the process. Classic CT signs of diverticulitis include:
- Presence of the diverticula themselves.
- Thickening of the intestinal wall.
- Inflammatory changes in the surrounding tissue: edema and fat stranding.
- Presence of fluid, which may extend along the root of the sigmoid mesocolon.
Abscesses are detected in 35% of cases. Localized fluid collections measuring less than 3 cm generally respond well to antibiotic therapy, whereas formations larger than 4 cm often require image-guided percutaneous catheter drainage.
Differential diagnosis: cancer or diverticulitis?
Imaging patterns of tumor and inflammation can have significant overlap, which sometimes greatly complicates diagnosis.
- Colorectal cancer: usually affects a short segment of the bowel, appearing as a mass-like wall thickening. It is often accompanied by regional lymph node enlargement. Ulceration and overhanging edges may be visible on CT.
- Diverticulitis: as a rule, involves a longer segment (greater than 10 cm). It is characterized by vascular engorgement and fluid accumulation in the mesentery.
Additionally, CT perfusion and MRI can be used for differentiation. On T2-weighted MRI scans in locally advanced cancer, tissue with intermediate signal intensity infiltrating the adipose tissue can be clearly seen.
Other complications of diverticular disease
Hemorrhage: Can be episodic and profuse. The mechanism is related to the fact that the intima of the vasa recta over the dome of the outpouching thickens, the wall weakens, and an eccentric rupture occurs, leading to massive bleeding.
Fistula formation: Chronic inflammatory infiltrate adheres to adjacent organs. The most common variant is a colovesical fistula (with the urinary bladder). The fistulous tract itself is not always visible on CT. Specific markers include: gas in the urinary bladder, thickening of its dome, a local abscess, and a closely adjacent bowel loop.
Giant cyst: A rare phenomenon representing a pseudocyst (without an epithelial lining). It occurs upon expansion of a walled-off subserosal perforation. It needs to be differentiated from a duplication cyst.
Other severe complications include volvulus and fecal peritonitis (occurring when an abscess ruptures into the free peritoneal cavity).
Epiploic appendagitis
A condition that clinically mimics acute diverticulitis (or appendicitis)—infarction of the epiploic appendage. The sigmoid or cecum is most commonly affected, where these appendages are largest. It presents with acute pain, but usually resolves spontaneously within a couple of weeks.
- On ultrasound: an oval, non-compressible hyperechoic mass directly beneath the abdominal wall.
- On CT: a high-density focus with a fat-density center.
Briefly: answers to topical questions
What classification is used to assess the severity of acute diverticulitis based on CT data?
Computed tomography is the most accurate method for determining the severity of the disease, although no specific CT classification is singled out in the sources. The following systems are used to assess the severity of diverticular disease and its complications:
- Hinchey classification — used exclusively for perforated diverticulitis.
- Hansen O., Stock W. classification — includes stages from uncomplicated diverticulitis to perforation into the free peritoneal cavity.
- Schreyer-Layer classification — noted as being very close to the Russian classification.
In which part of the large intestine are diverticula most frequently localized?
The sources do not specify which part of the large intestine most frequently contains diverticula. It is confirmed that diverticula of the right colon usually have wider necks, while rectal diverticula are extremely rare.
What radiological signs are characteristic of diverticular perforation into the free peritoneal cavity?
The main radiological sign of free diverticular perforation is the presence of free gas in the abdominal cavity.
- Pneumoperitoneum (Pneumoperitoneum) — on a upright radiograph, small gas accumulations are detected directly beneath the right hemidiaphragm.
- Cupola sign (Cupola sign) — free gas beneath the right and left hemidiaphragms may coalesce along the midline.
To differentiate diverticulitis from cancer on CT, remember the "D-D" rule: Diverticulitis is a Long segment (>10 cm) and Dendritic vessels (hyperemia), whereas cancer is a short segment with focal thickening.
Class and exam questions
Why can a diverticulum be mistaken for a polyp during CT colonography?
On 3D endoluminal reconstructions, a diverticulum filled with a dense fecolith bulges into the lumen and mimics a polyp. 2D images help distinguish them by revealing the structure of the fecalith with gas bubbles.
Which CT sign indicates the presence of a colovesical fistula?
A highly specific sign is the presence of gas in the urinary bladder lumen, especially if the patient has not recently undergone any urological interventions.
How does abscess size in diverticulitis affect treatment tactics?
Small fluid collections (less than 3 cm) are usually successfully treated conservatively with antibiotics. Abscesses larger than 4 cm often require catheter drainage under ultrasound or CT guidance.
What else to study on this topic
- Mechanism of false-positive polyp formation in CT colonography
- Pathogenesis of hemorrhage: the role of vasa recta intimal thickening
- CT perfusion in the differential diagnosis of colorectal cancer
- Formation of a giant pseudocyst and its differences from a duplication cyst
- Radiological appearance of epiploic appendagitis
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