CT-Based Determination of Ureteral Stone Volume: A Predictor of Spontaneous Passage

Which ureteral stone can pass spontaneously? It is hard to answer this question exactly. The size and location of the stone are the most important predictors. However, there is still a considerable gray zone that needs to be clarified. We try to identify the role of stone volume (SV) in the prediction of spontaneous passage (SP).

Seventy-eight patients with a solitary ureteral stone were retrospectively evaluated. Ureter SV measurements were taken in three planes and were calculated using the following formula: V = (X) × (Y) × (Z) × 0.52. SVs, and the longest diameters (LDs) were compared between patients who passed stones spontaneously and those who needed intervention.

The SVs and LDs were significantly lower in patients who passed stones spontaneously than in patients who required intervention (41.2 ± 35.5 vs 128.1 ± 91.1 mm(3), p = 0.001; 5.7 ± 1.8 vs 7.4 ± 1.7 mm, p = 0.001). The optimum cutoff values were 7.0 mm and 52.6 mm(3) for the LD and SV, respectively. For those stones of ≤7 mm, the volumes of the stones that could and could not pass did not differ significantly. However, the volume of the stones >7.0 mm that could pass was significantly higher than of those that could not. SP was 30.6% for stones >7 mm; however, when we removed the stones >52.6 mm(3), SP increased to 75% for stones higher than 7 mm (p = 0.001).

To classify ureteral stones using only one parameter such as stone diameter may lead to heterogeneity within the group. SV may be used in addition to size to determine a more definite homogeneous group to predict SP more precisely.