DOI: 10.1148/radiol.2291020690
(Radiology 2003;229:239-240.)
© RSNA, 2003
The Soft-Tissue Rim Sign1
Nizar A. Al-Nakshabandi, MB, FRCPC
1 From the Department of Radiology, Abdominal Division, Vancouver Hospital and Health Science Centre, British Columbia, Canada. Received June 9, 2002; revision requested July 16; final revision received October 2; accepted October 22. Address correspondence to the author, Department of Radiology, College of Medicine, King Saud University, Riyadh 11461, Saudi Arabia (e-mail: nizar97@hotmail.com).
Index terms: Signs in Imaging • Ureter, calculi, 82.811 • Ureter, CT, 82.12111
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APPEARANCE
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The soft-tissue rim sign has been described as being seen on unenhanced computed tomographic (CT) scans obtained in a patient suspected to have a ureteral calculus (1). It is recognized as an area of soft-tissue attenuation surrounding a suspended ureteral calculus that appears calcified (1) (Figure).
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EXPLANATION
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It has been suggested that the rim represents the edematous ureteral wall surrounding a ureteral stone (2).
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DISCUSSION
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The soft-tissue rim sign has evolved as a useful sign in the diagnosis of urolithiasis in patients with renal colic. The sign usually develops within 4–24 hours after obstruction (3). The soft-tissue rim sign has been found to have a sensitivity of 77% and a specificity reaching 92% (2).
Visualization of the soft-tissue rim sign is dependent on stone size; smaller ureteral calculi are more likely to exhibit this finding than are larger calculi. It has been postulated that larger calculi tend to thin the ureteral wall to a greater degree than do smaller stones, which makes detection of the ureteral wall more difficult. Heneghan et al (2) determined that the rim sign tends to be present with smaller stones (mean size, 4.3 mm) rather than with larger stones (mean size, 6.3 mm). This difference is statistically significant (P < .001), as 90% of the stones that measured 4 mm or less exhibited a rim sign, whereas stones that measured 5 mm or greater did not exhibit a rim sign. To my knowledge, no statistically significant difference in location of the stone or degree of obstruction has been shown for the rim sign (4).
The vast majority of ureteral calculi are of sufficiently high attenuation to be readily apparent on unenhanced abdominal CT scans. Occasionally, it may be difficult to differentiate a ureteral calculus from a phlebolith. This problem typically occurs in patients who are elderly, who have minimal retroperitoneal fat, or who have nonobstructing calculi (5). If the soft-tissue rim sign is present, it is useful in differentiating ureteral calculi from pelvic phleboliths in patients suspected of having ureteral colic. The soft-tissue rim sign is visible for 76% of ureteric calculi but only 2% of phleboliths (5). Smith et al (6) calculated the odds ratio of 31:1 comparing the frequency of the soft-tissue rim sign with calculi versus the frequency of the same sign with phleboliths. Results of another study, by Kawashima et al (1), showed that 50% of stones manifested a rim sign, 34% of stones were indeterminate for a rim sign, and 16% of the stones did not manifest a rim sign.
Therefore, a positive soft-tissue rim sign is helpful in making the diagnosis of ureterolithiasis. However, a negative soft-tissue rim sign does not preclude such a diagnosis (1) because it is absent in 16% of patients with ureterolithiasis.
This sign is generally seen in conjunction with other findings that suggest ureteral obstruction, such as hydronephrosis (sensitivity, 83%; specificity, 94%), ureteral dilatation with perinephric stranding of fat (sensitivity, 82%; specificity, 93%), or renal enlargement (sensitivity, 71%; specificity, 89%) (5). The recommended technique for CT examination is 5-mm collimations with reconstructions at 5-mm intervals (3).
In conclusion, identification of the soft-tissue rim sign at CT is valuable in diagnosing obstructing ureterolithiasis.
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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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REFERENCES
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- Kawashima A, Sandler C, Boridy IC, Takahashi N, Benson GS, Goldman SM. Unenhanced helical CT of ureterolthiasis: value of the tissue rim sign. AJR Am J Roentgenol 1997; 168:997-1000.[Abstract/Free Full Text]
- Heneghan JP, Dalrymple NC, Verga M, Rosenfield AT, Smith RC. Soft-tissue rim sign in the diagnosis of ureteral calculi with use of unenhanced helical CT. Radiology 1997; 202:709-711.[Abstract/Free Full Text]
- Smith RC, Levine J, Rosenfeld AT. Helical CT of urinary tract stones. Radiol Clin North Am 1999; 37:911-949.[CrossRef][Medline]
- Spencer BA, Wood BJ, Dretler SP. Helical CT and ureteral colic. Radiol Clin North Am 2000; 27:1-12.
- Bell TV, Fenlon HM, Davison BD, Ahari HK, Hussain S. Unenhanced helical CT criteria to differentiate distal ureteral calculi from pelvic phleboliths. Radiology 1998; 207:363-367.[Abstract/Free Full Text]
- Smith RC, Verga M, Dalrymple N, McCarthy S, Rosenfield A. Acute ureteral obstruction: value of secondary signs on helical CT. AJR Am J Roentgenol 1996; 167:1109-1113.[Abstract/Free Full Text]
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