DOI: 10.1148/radiol.2422041244
(Radiology 2007;242:632-633.)
© RSNA, 2007
The Gastrointestinal String Sign1
Gabriele Masselli, MD
1 From the Department of Radiology, University A. Gemelli, Largo A. Gemelli 8, 00168 Rome, Italy. Received February 20, 2004; revision requested September 28, 2004; revision received November 2; final version accepted December 14.
Address correspondence to the author (e-mail: gabrielemasselli{at}libero.it).
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APPEARANCE
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The gastrointestinal string sign is seen on small-bowel barium-enhanced images. It consists of a thin stripe of barium that resembles a frayed cotton string (Fig 1a) (1).
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Figure 1a: (a) Anteroposterior radiograph of early stage of single-contrast enteroclysis. A thin line of barium is seen in the terminal ileum (long arrows), which resembles a frayed cotton string (the gastrointestinal string sign). Small mesenteric border ulceration is seen (small arrow). (b) Further luminal distention overcomes the spasm, and the lumen is shown to be mildly distensible (lower arrow). Extensive ulcerations and fistulas (upper arrows) are evident.
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Figure 1b: (a) Anteroposterior radiograph of early stage of single-contrast enteroclysis. A thin line of barium is seen in the terminal ileum (long arrows), which resembles a frayed cotton string (the gastrointestinal string sign). Small mesenteric border ulceration is seen (small arrow). (b) Further luminal distention overcomes the spasm, and the lumen is shown to be mildly distensible (lower arrow). Extensive ulcerations and fistulas (upper arrows) are evident.
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EXPLANATION
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The gastrointestinal string sign results from a severe narrowing of a bowel loop, which makes the lumen resemble a string.
String sign is a term often applied to the appearance of any marked narrowing of the lumen, but it originated as a descriptor of reversible narrowing in Crohn disease (2–4). This narrowing is caused by incomplete filling as the result of irritability and spasms associated with severe ulceration, and it may be seen in both stenotic and nonstenotic phases of the disease (Fig 1b).
The degree of narrowing is not constant when narrowing is caused mainly by edema and accentuated by spasms. The diameter of the lumen does remain constant when marked fibrous thickening of the intestinal wall is present. The mucosa is replaced by a fibronecrotic membrane in which occasional islands of mucosa may still be found (5).
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DISCUSSION
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The gastrointestinal string sign has been identified as a manifestation of Crohn disease, and it is observed most frequently in the terminal ileum (6).
The iliac abnormalities associated with early Crohn disease include a coarse villous pattern, fold thickening, and aphthous ulcers. These findings alone are not pathognomonic of Crohn disease and can be seen in other diseases, but their presence can provide firm evidence of an early stage of the disease. Linear ulcers along the mesenteric border constitute one of the most important diagnostic features of small-bowel Crohn disease (7).
The ulcers run parallel to the shortened, concave, or straightened (and somewhat rigid) mesenteric border. The adjacent mesentery is thickened and retracted, especially at its junction with the affected bowel segment.
The rigidity of the mesenteric border is due to transmural inflammation that extends from the linear ulcer into the mesentery. As ulceration proceeds, spasms and irritability increase, the folds become more coarse and thickened, and the gastrointestinal string sign may be seen. The bowel proximal to the sign may or may not be dilated, depending on the stage of the disease. In the nonstenotic phase, the proximal intestinal lumen is generally not dilated (6), despite the narrowing associated with the string sign, which indicates the importance of edema, spasm and inflammation in producing this characteristic appearance.
This spasm is usually inconstant. Repeated spot radiographs demonstrate that some distensibility is present in this segment. However, when the spasm is persistent, temporary proximal dilatation may occur with symptoms of obstruction.
In the stenotic phase, there is a constant proximal dilatation that may be accentuated by spasms secondary to ulceration. Despite the narrowing, complete intestinal obstruction is rare (8).
The gastrointestinal string sign can be seen in other intestinal segments. Diseases other than Crohn disease can radiographically resemble a string, and alternate diagnoses should be considered. The sign is also seen in cases of pyloric stenosis as a single stripe of barium within the narrowed elongated pyloric channel (Fig 2) (9).
A carcinoid tumor can also result in the radiographic appearance of a gastrointestinal string sign (10). The radiologic signs shown at enteroclysis mirror the stage that the pathologic process has reached at the time of examination. If luminal narrowing and partial obstruction are present with carcinoid tumor, a string sign may result.
In conclusion, the gastrointestinal string sign is suggestive of Crohn disease, but it is also seen in other conditions. The sign indicates narrowing of the lumen of the small bowel, due either to spasm or stenosis.
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FOOTNOTES
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| A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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Author stated no financial relationship to disclose.
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References
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- Marshak RH. Granulomatous disease of the intestinal tract (Crohn's disease). Radiology 1975;114(1):3–22.[Abstract]
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- Kim SK, Carsky EW, Markarian B. Correlation conferences in radiology and pathology: diarrhea with string sign. N Y State J Med 1974;74(12):2190–2192.[Medline]
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