String sign | Radiology Signs

The string sign in the gastrointestinal tract is caused by severe luminal narrowing of a bowel segment, which results in a thin stripe of contrast material resembling a string on radiographic imaging. This narrowing often arises from chronic inflammation, spasm, fibrosis, or hypertrophy, leading to incomplete filling of the intestinal lumen. It is classically associated with Crohn’s disease (especially involving the terminal ileum), hypertrophic pyloric stenosis in infants, and can also be seen in conditions such as carcinoid tumors and colon cancer. In Crohn’s disease, ongoing ulceration and inflammation cause bowel wall thickening and spasm, whereas in hypertrophic pyloric stenosis, thickened pyloric musculature narrows the gastric outlet.

Why is it called so?

It is termed the “string sign” because on contrast studies—such as an upper GI series or small bowel follow-through—the severely narrowed bowel segment fills with a thin, linear column of contrast that appears like a slender string, visually representing only a thin remnant of the lumen amidst otherwise obstructed or stenotic bowel.

Pathophysiology:

The pathophysiology involves pathological narrowing of the bowel lumen due to transmural inflammation, ulceration, and fibrosis in Crohn’s disease; hypertrophic muscular thickening in pyloric stenosis; or mass effect from tumors causing stenosis. This luminal constriction permits passage of only a very narrow stream of contrast, producing the radiographic appearance of a thin, string-like channel of contrast material amidst the collapsed or thickened bowel wall.

Alternative names: String sign of Kantor

Other associated named signs: Railroad track sign (seen as parallel strings in hypertrophic pyloric stenosis)