Assessment of the clinical utility of the rim and comet-tail signs in differentiating ureteral stones from phleboliths

OBJECTIVE. This study was designed to assess interobserver variability in identifying the rim and comet-tail signs and to determine the clinical utility of these signs in determining whether or not the calcifications with which they are associated represent ureteral calculi. MATERIALS AND METHODS. Two radiologists and a radiology resident, unaware of the final diagnosis, reviewed preselected helical CT images from renal stone examinations in patients with 65 indeterminate pelvic calcifications. Assessment of calcifications for rim or comet-tail signs was performed independently of an assessment for the following five secondary signs of urinary tract obstruction: caliectasis, pelviectasis, ureterectasis, perinephric stranding, and renal enlargement. Agreement in identifying rim and comet-tail signs was assessed by obtaining kappa statistics. The utility the of rim or comet-tail signs in determining whether ureterolithiasis was present in patients in whom perinephric stranding and ureterectasis were present or absent was determined. The frequency with which one or more of each of the five assessed secondary signs was identified ipsilateral to a calcification having rim or comet-tail signs was also tabulated. RESULTS. Kappa values for interobserver agreement ranged from 0.49 to 0.73. In only one patient was a rim sign detected in the absence of ureterectasis and perinephric stranding. Reviewers identified at least three of the five assessed secondary signs ipsilateral to calcifications showing a rim sign in all but one patient (by each radiologist) and four patients (by the resident). When three or more secondary signs of obstruction were seen ipsilateral to a calcification having a comet-tail sign, in all but one instance, this was because the calcification was a ureteral calculus or because there was a separate ipsilateral ureteral calculus. CONCLUSION. In many instances, observers did not agree about whether the rim and comet-tail signs were present. The rim sign was observed in the absence of any secondary signs of urinary tract obstruction in only one (1.5%) of the 65 patients in our series (95% confidence interval, 0-5.3%). The comet-tail sign, when accompanied by secondary signs of obstruction, should indicate that an ipsilateral ureteral stone is present and not the reverse.