Ureterolithiasis: Value of the Tail Sign in Differentiating Phleboliths from Ureteral Calculi at Nonenhanced Helical CT

Illya C. Boridy, MD ; Paul Nikolaidis, MD ; Akira Kawashima, MD ; Stanford M. Goldman, MD ; Carl M. Sandler, MD

1 From the Department of Radiology, University of Texas Health Science Center at Houston, Tex. From the 1997 RSNA scientific assembly. Received January 28, 1998; revision requested April 7; revision received October 12; accepted November 9. Address reprint requests to I.C.B., Mallinckrodt Institute of Radiology, Washington University Medical Center, 9th Fl, Box 8131, 510 S Kingshighway Blvd, St Louis, MO 63110.

PURPOSE: To determine the value of the tail sign in differentiating phleboliths from ureteral calculi at nonenhanced helical computed tomography (CT).

MATERIALS AND METHODS: The nonenhanced helical CT scans in 82 patients with a confirmed diagnosis of pelvic ureterolithiasis were retrospectively reviewed. Each calcification along the ureter was classified as a phlebolith or a ureteral calculus on the basis of clinical and imaging findings and was analyzed for the presence of a tail sign.

RESULTS: Eighty-two patients each had a single ureteral calculus. None of these calculi were associated with a positive tail sign. Sixty-nine phleboliths were present in 35 patients. Forty-five phleboliths (65%) were associated with a positive tail sign. Of the remaining 24 phleboliths, 17 (25%) were associated with a negative tail sign and seven (10%) were indeterminate. The tail sign has a sensitivity of 65% (45 of 69; 95% CI: 53%, 75%) and a specificity of 100% (82 of 82; 95% CI: 96%, 100%) in differentiating phleboliths from ureteral calculi.

CONCLUSION: The tail sign is an important indicator that a suspicious calcification represents a phlebolith. Absence of the tail sign indicates that the calcification remains indeterminate.