Hydronephrosis of the kidneys occurs when urine backs up into the kidneys. This can be from a blockage that can occur anywhere along the urinary tract. Most commonly the blockage occurs in the ureters. The ureters are the tubes which carry urine from the kidneys to the bladder. Hydronephrosis can also occur from conditions which are not related to a blockage.
Hydronephrosis is a dilated collecting system
The kidneys are commonly evaluated on ultrasound. Hydronephrosis can be on one or both sides. Hydronephrosis can be mild to severe. On ultrasound, the kidney collecting system will become dilated. The collecting system of the kidney is where the urine goes before it drains into the ureter.
Can ultrasound tell us why there is hydronephrosis?
While ultrasound is excellent at diagnosing hydronephrosis, it is not a good test to tell us why the urine is backing up. Ultrasound is not good at showing us the ureters or tubes that drain urine. We also do not look at the bladder unless the ordering physician requests this. These are points of potential obstruction.
What causes hydronephrosis?
Often the blockage is in the ureters. This is most commonly from a stone, but can also be from a tumor, blood clot and stricture or narrowing. The blockage can also be in the bladder or urethra. The blockage is best shown by CT.
Hydronephrosis is most common from a stone which passes from the kidney. The stone will block the ureter causing a blockage. This is usually associated with rapid onset pain. The blockage or hydronephrosis is well seen on ultrasound. Often we need a CT to identity the stone and where it is causing the blockage.
Other causes of hydronephrosis like tumors or structures will have more chronic symptoms. Tumors of the ureters or bladder will often be associated with hematuria or blood in the urine. We often identity these tumors on CT scans called urograms. Ultrasound can not show the ureters well.
Hydronephrosis or dilated collecting systems can also be caused by conditions that do not block urinary flow. A mild to moderate degree of hydronephrosis can be caused by aggressive fluid administration or a full bladder. A patient who has previously had a blockage which is relieved may still have a dilated collecting system.
Reflux is when urine goes from the bladder into the ureters and kidneys. Infections of the urinary tract can cause the appearance of hydronephrosis. Often we can not identify these conditions on ultrasound and further testing is needed. A nuclear medicine renal scan is a test which can help us tell if the kidney is obstructed or not.
Hydronephrosis is frequently identified on kidney ultrasound. We can not tell the cause in many cases on ultrasound. We also don’t know if the kidney is obstructed with back up of urine flow, or if the appearance is from another condition which does not cause a blockage. There are other tests which can help us sort out the possibilities. The clinical information can also be helpful in reaching a diagnosis.
Hydronephrosis needs to be treated to prevent kidney function from deteriorating. The underlying cause will often be treated to relieve the obstruction. Sometimes procedures are done to bypass the obstruction and allow the urine backup to be relieved. This is done with catheters placed into the ureters or kidneys.