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string sign

String sign

The string sign may refer to:

  • angiographic string sign
  • gastrointestinal string sign
  • string sign of parosteal osteosarcoma

String sign bowel

The gastrointestinal string sign also known as the string sign of Kantor, refers to the string-like appearance of a contrast-filled bowel loop caused by its severe narrowing 1. String sign was originally used to describe a narrowed segment in regional ileitis due to the reversible narrowing caused by spasms in Crohn disease and not ulcerative colitis making this sign of significance. However, string sign is now used for any severe narrowing of the bowel lumen, including that seen in hypertrophic pyloric stenosis, gastrointestinal tuberculosis, carcinoid tumor and colon cancer 2.

String sign is a medical term often used in diagnosing hypertrophic pyloric stenosis. Specifically, it is a radiographic finding on an upper GI series in which the infant is given a radio-opaque material, such as barium, to drink. X-rays are then taken of the infant’s stomach and intestines.

If the infant has pyloric stenosis, the pylorus is narrowed and the barium will take on the appearance of a thin string as it passes through this narrowed channel. Often, there are several of these strings seen called the “railroad track sign”. The use of the upper GI series for the diagnosis of hypertrophic pyloric stenosis, which was the primary diagnostic tool for this condition in the 1980’s and 1990’s, has been largely replaced by the use of ultrasound, which is less invasive and can visualize the thickened pylorus, giving actual measurements of this thickening.

Figure 1. String sign

string sign barium

Footnote: Young adult male with known Crohn’s disease with worsening symptoms. Long segment of narrowed terminal ileum in a ‘string like’ configuration in keeping with a long stricture segment. Termed the string sign of Kantour (gastrointestinal string sign).

String sign artery

The angiographic string sign, also known as the carotid string sign, refers to the thin string of intravenous contrast material distal to a stenotic focus in the internal carotid artery. A thin stripe of flow is caused by decreased pressure and flow distal to the stenosis, which causes a collapse of the distal internal carotid artery.

An angiographic string sign may be caused by 3:

  • Pre-occlusive atherosclerosis at the carotid bifurcation
  • Internal carotid artery dissection
  • Internal carotid artery thrombosis
    • Subacute partial
    • Chronic subtotal
  • Partial recanalization of an occluded internal carotid artery
  • Stenosis secondary to radiation

Figure 2. Carotid string sign

angiographic string sign

String sign bones

The string sign of parosteal osteosarcoma refers to the plain radiographic/CT appearance of a radiolucent cleavage plane between portions of the tumor and cortex of the affected bone 4. The tumor stalk becomes more broad-based with time, obliterating the string sign in later stages.

The string sign can also be seen in myositis ossificans.

Figure 3. String sign of parosteal osteosarcoma

string sign of parosteal osteosarcoma
References
  1. Kantor JL. Regional (Terminal) Ileitis: its roentgen diagnosis. JAMA. 1934;103(26):2016–2021. doi:10.1001/jama.1934.02750520018005
  2. The Gastrointestinal String Sign. Radiology. 2007;242 (2): 632-3. https://doi.org/10.1148/radiol.2422041244
  3. The angiographic string sign. Radiology. 2002 Jan;222(1):237-8. https://doi.org/10.1148/radiol.2221000366
  4. Parosteal osteosarcoma: radiologic-pathologic correlation with emphasis on CT. AJR Am J Roentgenol. 1987 Feb;148(2):323-8. https://www.ajronline.org/doi/pdf/10.2214/ajr.148.2.323
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