Accordion sign | Radiology Signs

Answer:

The accordion sign is alternating high- and low-attenuation bands across a thickened colonic wall on contrast-enhanced CT. The high-attenuation bands are positive oral contrast trapped in the deep clefts between markedly thickened, oedematous haustral folds and adherent pseudomembranes; the low-attenuation bands are the oedematous mucosa and submucosa themselves. The result is a striped, pleated appearance across the lumen. It is best known in fulminant pseudomembranous colitis from Clostridioides difficile, but it is a marker of severe colonic wall oedema rather than of any one organism: it is also described in ischaemic colitis, inflammatory bowel disease, cirrhosis with hypoalbuminaemia and portal hypertension, and in cytomegalovirus, Salmonella and Shigella colitis. Its sensitivity for C. difficile is poor, so its absence excludes nothing, but when present it indicates severe transmural oedema and should prompt assessment for toxic megacolon and perforation. Note that it requires positive oral contrast, so it is not seen on the water-only or non-contrast studies now often used.

Why is it called so?

The alternating dense and lucent bands across the thickened wall resemble the folded bellows of an accordion.

Pathophysiology

Severe colitis produces intense submucosal oedema and inflammatory infiltration, which thickens the haustral folds several-fold and deepens the interhaustral clefts. Positive oral contrast entering the lumen is squeezed into these narrow clefts and is held there, while the swollen low-attenuation folds separate one contrast-filled cleft from the next. In pseudomembranous colitis, adherent fibrinopurulent pseudomembranes add to the fold thickening and further trap contrast. Because the mechanism is mechanical trapping of contrast between grossly thickened folds, any cause of comparably severe colonic oedema can reproduce it.

Alternative names: Accordion pattern

Other associated named signs: Target sign and mural stratification, the pericolonic stranding of severe colitis, and the thumbprinting sign on the abdominal radiograph

References

1. Kirkpatrick ID, Greenberg HM. Evaluating the CT diagnosis of Clostridium difficile colitis: should CT guide therapy?. AJR Am J Roentgenol. 2001;176(3):635-9. PMID: 11222194.