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Comet tail sign : Urology

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

The comet-tail sign (in urological imaging) is helpful in distinguishing a ureteric calculus from a phlebolith, and strongly favours the later.

The sign refers to a tail of soft tissue extending from a calcification, representing the collapsed / scarred / thrombosed parent vein. When well seen it is said to have a positive predictive value of 100% ¹.