Picture of the Month—Diagnosis FREE

The upper gastrointestinal series with barium contrast (Figure 1) shows marked narrowing and nodularity of the terminal ileum consistent with Crohn disease and is termed a string sign. This gastrointestinal string sign, which is seen on small bowel contrast images, is a result of severe inflammation in the affected bowel segment. Kantor¹ uses the term string sign to describe the thin linear shadow, which resembles a cotton string, progressing through a filling defect in the ileum that extends to the ileocecal valve, in patients with Crohn disease.

Linear ulcers that run parallel to the mesenteric border of the terminal ileum are an important feature associated with small-bowel Crohn disease. Although not pathognomic of Crohn disease, abnormalities of the terminal ileum, including ulceration and mucosal thickening, are diagnostic of disease activity.^2- 3 Because of extensive transmural inflammation extending from the linear ulcer into the mesentery, a rigid mesenteric border and a contracted bowel lumen develop.⁴

The narrowed segment seen as the gastrointestinal string sign is the result of severe inflammation, irritation, and spasm associated with the significant ulceration.⁵ Typically, the spasm is not constant and is not associated with dilatation of the proximal bowel segment. However, the proximal intestine can be found to have temporary or constant dilatation depending on the frequency of spasms. Clinically, this may occur with symptoms of obstruction, although complete intestinal obstruction is rare. Figure 2, taken 4 hours after oral administration of enteric contrast, illustrates a temporary dilatation of a proximal small-bowel segment that is not visualized in the prior image (Figure 1), which was taken 3 hours after oral administration of enteric contrast and during the upper gastrointestinal series.

Although easy to recognize when seen, the gastrointestinal string sign can be seen in other segments of the intestine.⁶ Therefore, care must be made not to confuse the string sign associated with Crohn disease with other disease processes that have similar radiographic findings.

A contrast-filled appendix can sometimes be seen, but it has a more constant luminal diameter, lack of mucosal irregularity, and lack of peristalsis distinguishing it from an abnormal segment of small bowel exhibiting the string sign. A string sign is also seen radiographically in pyloric stenosis, which results from a single band of contrast in the thinned and elongated pyloric channel.

Other pathological lesions can also present a similar picture to the string sign in the region of the terminal ileum. A carcinoid tumor can produce this finding if luminal narrowing and partial obstruction are associated. Circumscribed tuberculomas and stenosing sarcomas of the terminal ileum may result in a string sign as well. Finally, there have been reports that syphilis of the terminal ileum may have a similar radiographic appearance.

Because Crohn disease can occur at any location in the gastrointestinal tract, upper and lower endoscopies allow for the visual examination of the mouth, esophagus, duodenum, terminal ileum, and colon as well as for the performance of biopsies that may show typical granulomatous changes on histology. Capsule endoscopy allows direct visualization of the small intestine, although it should be avoided in patients with intestinal strictures. Use of barium contrast agents in the small intestine provides for an adequate study to evaluate for small-bowel disease. Computed tomographic and magnetic resonance enterographic images of the small intestine can show mucosal and mural edema and can also show complications such as abscess formation. Magnetic resonance enterography also has the benefit of no ionizing radiation, which can become significant in patients with Crohn disease who undergo multiple computed tomography and fluoroscopic imaging of the abdomen. Unfortunately, to our knowledge, no imaging study is currently specific enough to confirm a diagnosis of Crohn disease. Current laboratory methods for evaluating possible Crohn disease, such as elevated levels of fecal calprotectin, neutrophil-associated protein, and serum antibodies to Saccharomyces cerevisiae, are more useful to support the diagnosis, rather than serve as a diagnostic test, because of poor sensitivity and specificity.

Although this classic radiographic finding is seen in other organic diseases, the string sign represents luminal narrowing of the small intestine with associated spasm and/or stenosis. Although not pathognomonic, the gastrointestinal string sign is highly suggestive of Crohn disease.

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