Objective: The purpose of this study was to asses the accuracy of criteria in distinguishing distal urinary stones from phleboliths defined in the literature with thin-slice unenhanced helical computed tomography (CT).

Materials and Methods: Between October 2004 and April 2005, we performed 3 cm length thin-slice (2 mm section thickness, pitch:1) helical CT on 31 patients with urinary stones and on 43 patients with 80 phleboliths. The size, shape, central lucency, soft tissue rim sign, comet-tail sign, density values and profile analysis of each calcification were recorded.

Results: Fifty two (65%) of 80 phleboliths were round and 28 (35%) were oval shape. On the contrary, ten (32%) of 31 stone were round, 8 (26%) of them were of oval shape. Geometric configuration was seen in thirteen (42%) stones but not in any phleboliths. Mean densities of phleboliths and stones were 386,5 HU (131 HU/935 HU) and 1088 HU (526 - 1594), respectively. This difference was statistically significant (p<0,05). Eighteen (23%) of 80 phleboliths had central lucency and bifid peak on profile analysis. All 31 stones had a single peak at profile analysis. Although comet-tail sign was seen at 12 (15%) of 80 phleboliths, we did not observe this sign at stones. We observed soft tissue rim sign on 21 (67%) of 31 stones. However this sign was never seen on phleboliths.

Conclusion: The results of this study indicate that unenhanced helical CT has reliable findings in the differentiation of stones from phleboliths. It is easier to differentiate urinary stones from phleboliths with thin-slice CT. Applying of all criteria mentioned in this study may be useful in differentiation of distal urinary stones from phleboliths on unenhanced helical CT.