Hydronephrosis can occur on a temporary basis as during pregnancy, due to compression made by the uterus on the ureters, but other possible causes of hydronephrosis are:
- Union of the ureter to the renal pelvis is too high; Torsion of the ureteropelvic junction due to a displacement of the kidney downward; Calculations located in the renal pelvis; Compression of the ureter by fibrous bands, by an abnormally located artery or vein or by a tumor; Obstruction located below the ureteropelvic junction or the retrograde flow of urine from the bladder, due to stones located in the ureter; tumors of the ureter or nearby; ureteral stenosis as a result of a congenital defect, injury, infection, radiation therapy or exploratory surgery; disorders of the muscles or nerves of the ureter or bladder; formation of fibrous tissue in the ureter or in around the same due to surgery, radiotherapy or medications such as methylergide; Ureterocele (sliding of the lower end of a ureter into the bladder); Bladder, cervix, uterus, prostate or other pelvic organs cancers; Severe urinary tract infection, which temporarily prevents the ureter from contracting.
In the case of hydronephrosis caused by pregnancy, hormonal changes during pregnancy can aggravate the problem, by reducing the muscular contractions of the ureters that normally move the urine to the bladder, but this type of hydronephrosis usually ends at the end of the pregnancy.
