If unilateral, it may be due to obstruction at the level of the ureteral orifice and above, as from a calculus or neoplasm, or less commonly a stricture from inflammation.

• 如为单侧肾脏病变阻塞部位位于输尿管及以上，如结石、肿瘤或较少见的炎症所致的狭窄。