Radiography
This radiograph demonstrates a greatly dilated sigmoid that almost fills the entire abdomen (same patient in Images 1-3). Note the coffee bean sign. The remainder of the large bowel is not dilated, presumably because the proximal point of the twist is not causing obstruction and thus allows drainage into the sigmoid.
Erect abdominal radiograph (same patient in Images 1-3). This image shows fluid levels in the distended sigmoid loop.
This radiograph shows decompression of the sigmoid loop following retrograde passage of a flatus tube (same patient in Images 1-3).
Supine abdominal radiograph in a 6-year-old child from an area in which roundworms are endemic. This image shows a sigmoid volvulus. The sigmoid loop is dilated and associated with mild proximal large-bowel dilatation.
This erect radiograph shows fluid levels in the sigmoid loop and in the transverse colon (same patient as in Image 4).
Erect abdominal radiograph demonstrating a giant sigmoid diverticulum. This image shows a dilated loop of bowel with air-fluid levels and intraluminal feces. This appearance mimics that of an enlarged cecum or sigmoid loop.
Radiograph from an enema examination with water-soluble contrast material in an unprepared bowel (same patient as in Image 6). This image shows a giant sigmoid diverticulum that contains feces.
Findings
- Plain radiographs show a markedly distended sigmoid loop, which assumes a bent inner tube or inverted U -shaped appearance, with the limbs of the sigmoid loop directed toward the pelvis.
- The colonic haustra are lost, and progressive distention elevates the sigmoid loop under one side of the diaphragm.
- An upright radiograph shows a greatly distended sigmoid loop with air-fluid levels mainly on the left side of the abdomen and extending toward the right hemidiaphragm.
- The involved bowel walls are edematous, and the contiguous walls form a dense white line on radiographs. This line is surrounded by the curved and dilated gas-filled lumen, resulting in a coffee bean-shaped structure; this is the coffee bean sign.11
- If more fluid than air is in the obstructed loop of the sigmoid, the volvulus may be demonstrable by a soft-tissue mass or a pseudotumor sign.
- A single-contrast barium enema examination is adequate because the barium readily enters the empty rectum and usually encounters a complete stenosis, which is likened to a beak, the so-called bird's beak or bird-of-prey sign.
- If barium can enter the obstructed segment, spiraling of the mucosal folds may be seen. Signs of bowel ischemia, such as thumbprinting, transverse ridging, and mucosal ulceration, may be observed.
- A dilated sigmoid colon that ascends to the transverse colon (northern exposure sign) is said to be a reliable sign of a sigmoid volvulus on a supine abdominal radiograph.12
Degree of Confidence
In 60-70% of patients, the diagnosis of sigmoid volvulus can be made by using plain abdominal radiographic findings. In 20-30% of patients, the 2 limbs of the twisted sigmoid colon may overlap or deviate to the right or left, obscuring the remainder of the colon. In these instances, the findings are those of a nonspecific large-bowel obstruction, and barium enema examination is required for confirmation of the diagnosis.
False Positives/Negatives
Other forms of large-bowel obstruction, especially those due to sigmoid colon carcinoma, pseudo-obstruction, cecal volvulus, and an ileosigmoid knot, may mimic or be confused with a sigmoid volvulus. At times, emphysematous cystitis and a giant sigmoid diverticulum may also mimic a sigmoid volvulus.
Computed Tomography
Findings
- CT scan findings of sigmoid volvulus include the whirl sign, which represents tension on the tightly twisted mesocolon by the afferent and efferent limbs of the dilated colon.13,14
- CT scanning may be useful in identifying the etiology and site of the obstruction that result from other pathologies, as well as in demonstrating ischemia that results from strangulation.
- CT scan signs of ischemia include a serrated beak at the site of the obstruction, mesenteric edema or engrossment, and moderate to severe thickening of the bowel wall.
- Intramural gas or portal venous gas may be seen (grave prognostic signs), and in patients in whom a perforation has occurred, a large amount of free intraperitoneal gas or fluid may be noted.
Degree of Confidence
CT scanning is the least invasive imaging technique that allows assessment of mural ischemia. This imaging modality helps in identifying the cause of an acute large-bowel obstruction in 74-86% of cases, although the sensitivity of the investigation is not yet defined.
False Positives/Negatives
False-positive findings may involve other forms of volvulus or obstruction and causes of large-bowel ischemia.
Magnetic Resonance Imaging
Findings
MRI has been used successfully in the assessment of large-bowel obstruction (not specifically in sigmoid volvulus). These examinations were performed with the retrograde insufflation of 1000-1200 mL of air through a Foley catheter that was placed in the rectum and with scopolamine to inhibit peristalsis in order to demonstrate the site of bowel obstruction. In addition, MRI has been used in the diagnosis of mural necrosis in infants and, theoretically, this modality can be used in adults.
Degree of Confidence
With limited experience at the present stage in using this imaging modality to evaluate sigmoid volvulus, assessing the degree of confidence with MRI is not possible.
False Positives/Negatives
With the present experience, the limitations of MRI regarding false-positive findings of sigmoid volvulus are not known.
Ultrasonography
Findings
Ultrasonography might occasionally be useful in assessing large-bowel obstruction.15,16
Degree of Confidence
The confidence level of ultrasonography is low in the diagnosis of sigmoid volvulus.
False Positives/Negatives
In the limited experience in diagnosing sigmoid volvulus by ultrasonography, the images fail to depict the cause in most patients.
More on Sigmoid Volvulus |
| Overview: Sigmoid Volvulus |
 Imaging: Sigmoid Volvulus |
| Follow-up: Sigmoid Volvulus |
| Multimedia: Sigmoid Volvulus |
| References |
| Further Reading |
| « Previous Page | Next Page » |
References
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Further Reading
Related eMedicine topics
Obstruction, Large Bowel [Emergency Medicine]
Colonic Obstruction [Gastroenterology]
Megacolon, Toxic [Gastroenterology]
Megacolon, Chronic [Gastroenterology]
Toxic Megacolon [Radiology]
Keywords
sigmoid volvulus, intestinal torsion, gastrointestinal tract, sigmoid colon, large bowel, chronic constipation, roundworm, large bowel obstruction, large-bowel obstruction, pneumoperitoneum
