Kinking of the upper ureter in CT urography: anatomic and clinical significance

Purpose: Although the course of the ureter is described as a straight descent in the retroperitoneum, kinking of the upper ureter is often seen at imaging. The aim of this study was to investigate kinking of the ureter and its underlying anatomico-clinical significance. Methods: We evaluated 176 computed tomography (CT) images and classified kinking into three grades: no/mild kinking as Grade 1, moderate as Grade 2, and severe as Grade 3. We defined the “crossing point” (CP) as where the ureter crosses over the gonadal vein and assessed its relation to the kinking. Fourteen halves from seven cadavers were used for examination. Approaching anteriorly, we macroscopically observed the ureter and surrounding structures. Results: On CT, the rate of the radiologically “significant” kinking classified into either Grade 2 or 3 was 18.4 % on the right and 21.8 % on the left. All kinking was either at or above the level of the CP. In cadavers, the ureter was relatively mobile in the perirenal fat and then beginning at approximately the level of the CP became firmly fixed to the anteromedial aspect of the psoas major muscle. Conclusions: Kinking of the upper ureter is not a clinically significant finding and arises from the ureter having a relatively mobile portion in the perirenal space compared to its caudal portion. The fixation boundary can be identified by observing the CP.