Causes

Different types of ureteral obstruction have different causes, some of them present at birth (congenital). They include:

Ureteral obstruction may be caused by:

• Duplication of the ureter, the tube that carries urine from the kidney to the bladder. This common condition, which is present at birth (congential), causes two ureters to form on the same kidney. The second ureter can be normal or only partially developed. If either ureter doesn't function properly, urine can back up into the kidney and cause damage.
• An abnormality where the ureter connects to the bladder or the kidney, which blocks urine flow. An abnormal connection between the ureter and kidney (ureteropelvic junction) may cause the kidney to swell and eventually stop working. This abnormality can be congenital or it can develop with normal childhood growth, result from an injury or scarring, or in rare cases, develop from a tumor. An abnormal connection between the ureter and bladder (ureterovesical junction) may cause urine to back up into the kidneys.
• Ureterocele. If the ureter is too narrow and doesn't allow urine to flow normally, a tiny bulge in the ureter (ureterocele) may develop, usually in the section of the ureter closest to the bladder. This can block urine flow and cause urine to back up into the kidney, possibly leading to kidney damage.
• Retroperitoneal fibrosis. This rare disorder occurs when fibrous tissue grows in the area behind the abdomen. The fibers may grow due to cancers or may result from taking certain medicines used to treat migraines. The fibers encircle and block the ureters, causing urine to back up into the kidneys.

Other possible causes

Various causes inside (intrinsic) or outside (extrinsic) the ureter can lead to ureteral obstruction, including:

• Ureteral stones
• Severe constipation, which happens primarily in children but also occurs in adults
• Cancerous and noncancerous tumors
• Internal tissue growth, such as endometriosis in females
• Long-term swelling of the ureter wall, usually due to diseases such as tuberculosis or a parasite infection called schistosomiasis