Does Side Make a Difference? Anatomical Differences between the Left and Right Ureter

Objectives Seventy to eighty percent of iatrogenic ureteral injuries involve the left ureter. We sought to evaluate potential anatomical differences between the left and right ureters that may contribute to this discrepancy. Methods A retrospective image review was undertaken of women who underwent computed tomography urograms between 2012 and 2013. The distance to the ureters from the midline was measured at the level of the sacral promontory (S₁) and the cervix. Cervical deviation from the midline was measured, and distance between the cervix and ureters was calculated. The anterior-posterior distance between ureters was also measured. Results Ninety-five computed tomography urograms were analyzed. The mean age was 56 years (range, 23-92 years). Mean cervical deviation was 2.9 mm left of the midline (P = 0.028). The left ureter was 4.2 mm more lateral than the right at S₁ and 2.7 mm more lateral at the cervix (P = 0.000 and 0.001). There was no significant difference when accounting for cervical deviation (P = 0.220). The left ureter was 1.9 mm more anterior than the right at the cervix (P = 0.012). Age, body mass index, and ethnicity did not affect the ureteral position. Conclusions Based on midline measurements, the left ureter courses 2 to 4 mm more lateral and anterior than does the right ureter. The cervix is also positioned 2 to 4 mm to the left side, and as a result, the ureters are actually symmetric to the cervix. Although seemingly small, 2 to 4 mm is the width range of a Heaney clamp. These anatomic differences may be a contributing factor to the increase in ureteral injuries on the left side compared with the right.