What causes the soft tissue rim sign in the ureter on computed tomography (CT)?
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The soft tissue rim sign on CT is caused by the presence of an obstructing intraureteral calculus surrounded by a rim of edematous ureteric wall. This sign indicates ureteral obstruction leading to inflammation and localized wall edema. It is commonly seen in patients with ureteric calculi causing ureteral obstruction and flank pain. Clinically, it helps differentiate ureteric stones from phleboliths, which usually lack this rim due to the absence of surrounding ureteric wall edema.
Why is it called so?
It is named the “soft tissue rim sign” because it appears as a circumferential rim of soft tissue attenuation encircling a calcific density within the ureter. This rim corresponds anatomically to the edematous and inflamed ureteric wall immediately adjoining the obstructing stone.
Pathophysiology
The sign develops because an obstructing ureteric calculus induces localized ureteral wall inflammation and edema. The resultant swelling of the ureteric mucosa and muscularis forms a visible soft tissue rim on CT around the dense stone. This rim typically measures 1–2 mm in thickness and has attenuation values of about 20–40 Hounsfield units, reflecting inflamed soft tissue adjacent to the high-density calculus.
Alternative names:
None
Other associated named signs:
Comet-tail sign (seen with phleboliths, helping differentiate from ureteric stones)
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