Imaging findings in sigmoid and cecal volvulus
When sigmoid volvulus (volvulus coli sigmoidei) is suspected, abdominal plain radiography serves as the primary imaging modality. The physician identifies a pathognomonic marker—the "coffee-bean" sign ('coffee-bean' sign). It is formed by a markedly dilated, gas-filled intestinal loop that originates in the pelvic cavity and extends abnormally into the left upper quadrant of the abdomen. Contrast-enhanced computed tomography (CT) is used for topographical diagnosis. Coronal reconstructions clearly demonstrate the twisting of the nourishing vessels within the sigmoid mesocolon. This phenomenon is referred to as the "whirl sign" ('whirl sign') and is typically localized at the level of the pelvic brim.
A similar biomechanical mechanism is observed in cecal volvulus (caecal volvulus), although the imaging findings differ. On a supine radiograph, the cecum appears inverted and extremely dilated. It shows an atypical displacement from the right side of the abdomen upward, reaching the left upper quadrant. Computed tomography confirms the presence of a distended loop and demonstrates the "whirl sign," but localized to the right lower quadrant.
Although bowel wall thickening, outlined by gas and adjacent adipose tissue, can be observed on conventional radiographs, CT has a higher sensitivity, particularly for detecting small gas collections within the bowel wall itself.
Large-bowel ischemia
Large-bowel ischemia (large-bowel ischaemia) clinically manifests as sudden abdominal pain, soon followed by bloody diarrhea. Anatomically, the most vulnerable zones are the splenic flexure and the proximal descending colon. This specific localization is explained by the fact that this segment is situated within a hemodynamic "watershed" (watershed) area—at the boundary between the superior and inferior mesenteric artery supply territories.
Morphologically, ischemia manifests as hemorrhage and edema, leading to marked bowel wall thickening (primarily of the submucosa). On radiographs and CT scans, this edema is visualized as the "thumbprinting" sign (thumbprinting). The ischemic segment loses peristalsis and functions as an obstructing lesion, causing secondary distention of the right colon. In the chronic stage, the damaged area may undergo fibrosis, resulting in a stricture.
Inflammatory bowel disease and pseudomembranous colitis
Plain abdominal radiography (AXR) allows assessment of the degree of colonic involvement in acute inflammatory bowel disease (inflammatory bowel disease). The state of the mucosa, presence of gas, and fecal matter are analyzed. It has been established that the amount of stool correlates with the severity of colitis: formed fecal residue (faecal residue) indicates an inactive phase of the disease, whereas its absence signifies extensive involvement. Intraluminal gas serves as a natural contrast—without it, mucosal changes may go unnoticed.
A formidable complication is toxic megacolon (toxic megacolon). This high-risk condition is characterized by pathological colonic dilation, loss of haustra, and deep ulcers penetrating the muscular layer. It requires emergency surgical intervention, making daily AXR monitoring indicated.
Pseudomembranous colitis, associated with antibiotic use (clindamycin, lincomycin), is a distinct entity. The primary pathogen is the bacterium Clostridium difficile. Imaging findings are detected in 32% of patients and include bowel dilation, haustral thickening, mucosal abnormalities (18% of cases), and the thumbprinting sign. The process can involve the entire colon, but the transverse colon and, in most cases, the rectum are most frequently affected.
Briefly: answers to topical questions
What are the diagnostic criteria and complications of toxic megacolon on plain radiographs?
On plain radiographs, the diagnostic criteria for toxic megacolon are marked colonic dilation and the absence of haustra.
Criteria and features:
- Colonic dilation — enlargement may exceed 8.5 cm, with gas-filled ascending and transverse colons showing a thickened wall.
- Loss of haustration (haustration) — indicates transmural inflammation; if haustra are preserved, the diagnosis is excluded.
- Mucosal changes — ulcerations penetrate into the muscular layer.
The primary complication of this condition is bowel wall perforation.
Which vessels are involved in sigmoid volvulus?
In sigmoid volvulus, the vessels running within its mesentery are involved in the pathological process.
Contrast-enhanced computed tomography visualizes vascular torsion in the sigmoid mesocolon (sigmoid mesocolon). This creates the characteristic radiological "whirl sign" (whirl sign) at the pelvic inlet. Specific names of the involved arteries and veins in the context of the volvulus imaging findings are not detailed in the sources.
To memorize the typical localization of large-bowel ischemia, use the "watershed" association: the splenic flexure lies at the boundary of two arterial territories, much like the peak of a hill where water (blood) arrives last when pressure drops.
Class and exam questions
How to differentiate sigmoid volvulus from cecal volvulus on a plain radiograph?
The sigmoid colon forms the "coffee-bean" sign and extends from the pelvis into the left upper quadrant. When twisted, the cecum dilates and shifts upward and to the left from the right side of the abdomen.
What does the "thumbprinting" sign mean on a scan?
This is a radiological term reflecting marked submucosal thickening due to edema or hemorrhage. It is characteristic of bowel ischemia, severe colitis, and pseudomembranous colitis.
Why assess stool quantity on a radiograph in colitis?
The volume of fecal matter correlates with the extent of inflammation. The presence of formed stool suggests that the process is likely inactive, whereas its complete absence is a sign of extensive colitis.
What is the danger of toxic megacolon?
This is a life-threatening condition in which the colon dilates severely, haustra disappear, and ulcerations destroy the muscular layer, creating a high risk of perforation and necessitating evaluation for emergency surgery.
What else to study on this topic
- CT anatomy of the sigmoid mesentery vessels and the pelvic brim.
- The biomechanics of the "whirl sign" formation in various types of volvulus.
- Differential diagnosis of causes of colonic submucosal thickening.
- Pharmacological characteristics of clindamycin and lincomycin in the context of pseudomembranous colitis development.
- Pathogenesis of stricture formation as a late consequence of intestinal ischemia.
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