General Considerations

• Finding seen on contrast studies using primarily barium
• Originally described in the terminal ileum in Crohn’s disease and that is its most common usage
• Initially, it is caused by severe spasm secondary to irritability of the loop producing the appearance of a frayed cotton string
• At first, edema and spasm narrow the loop but the narrowing is at least partially distensible
• Eventually the wall of the ileum may become fibrotic and the lumen fixed in diameter

Clinical Findings

• Right lower quadrant crampy abdominal pain

Imaging Findings

• Persistently narrowed but potentially distensible terminal ileum
• First sign of Crohn’s ileitis is usually shallow aphthous ulcers
• Short, linear ulcers along the mesenteric border may also be seen with Crohn’s ileitis
• Induration of the surrounding fat may cause the loop to be separated from the other small bowel loops (proud loop)
• Bowel proximal to the narrowed segment may or may not be dilated
  • This is because of the intermittent nature of the spasm associated with the sign
• When the wall becomes fibrotic and the luminal narrowing fixed, it is more likely for the proximal bowel to be dilated
• High grade small bowel obstruction does not usually occur whether the ileum is narrowed from spasm or fibrosis

Differential Diagnosis

• The term “string sign” may also be applied to other narrowed loops of small bowel, particularly in Crohn’s disease
• Carcinoid tumors may produce similar findings in the ileum
• Another “string sign” may be seen in an elongated and narrowed pylorus caused by hypertrophic pyloric stenosis
  • There are also unrelated “string signs” used in angiography and in describing parosteal sarcomas

 

 

String Sign-Crohn's Disease. On left, white arrow points to markedly narrowed terminal ileum. The black arrow indicates that the proximal loops of small bowel are nor dilated. On the right, in another patient with the same disease and finding, the white arrow points to another string sign of the terminal ileum from Crohn's. Notice how the terminal ileum sits separately from the rest of the small bowel loops due to increase fat in the mesentery (proud loop).
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