The Peak Site of Stone Distribution in the Upper Ureter is Unlikely the Ureteropelvic Junction: Computed Tomography Analysis of Stone Lodging Site With Respect to a Newly Identified Area of Constriction.

OBJECTIVE

To investigate the relationship between the upper urinary stone distribution and the "crossing point," an area of relative fixation within the upper ureter at approximately the level where the ureter crosses the gonadal vein.

MATERIALS AND

METHODS

We reviewed 298 consecutive patients presenting with acute renal colic, identified upper ureteral stones in computed tomography. For stones located at the "renal pelvis and upper ureter," we measured the vertebral level of each renal pelvis, crossing point, and stone. The distance between the crossing point and the stones (designated as positive if the stone was located above it) and the distance between the renal pelvis and the crossing point were measured.

RESULTS

The average stone size at the "renal pelvis and upper ureter" was 6.0 ± 3.2 mm, at "middle ureter" 5.2 ± 1.9 mm, and at "lower ureter" 3.7 ± 1.8 mm. Lower location was significantly correlated with smaller size (P <.001). The level of the crossing point and stone location were significantly lower on the right (P = .019, P = .033, respectively), whereas the vertebral level of the renal pelvis was not significantly different on both sides (P = .225). The mean distance between the crossing point and the stones was -5.6 ± 18.4 mm (median: 0 mm) on the right and -4.7 ± 19.3 mm (median: 0 mm) on the left. The mean distance between the renal pelvis and the stones was significantly longer on the right (57.2 ± 18.5 mm and 48.2 ± 19.1 mm) (P = .038).

CONCLUSION

The crossing point is the peak site of stone distribution in the upper ureter and likely different from the traditionally identified obstruction site at the ureteropelvic junction.