Hydronephrosis is a common abnormality of the kidney found on various imaging studies. This occurs when urine builds up in the kidney and causes it to swell. Hydronephrosis can result from a blockage of the urine outflow from the kidney or from reflux of urine into the kidney.
What is hydronephrosis?
The term hydronephrosis refers to a dilated kidney collecting system. The collecting system of the kidney is where the urine is collected in the kidney before it drains into the ureter and then the bladder.
Hydronephrosis has many causes, some of which block the outflow or urine anywhere along the urinary tract and others which are not associated with blockage.
Hydronephrosis of the kidneys occurs when urine backs up into the kidneys and causes it to swell. 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 like reflux of urine from the bladder into the kidney. Hydronephrosis can sometimes persist after the blockage or reflux is corrected.
Symptoms of hydronephrosis
Flank or back pain is common. Nausea, vomiting, urinary symptoms such as urgency or increased frequency.
How is hydronephrosis diagnosed?
Hydronephrosis is commonly diagnosed on ultrasound and CT exams. Hydronephrosis can occur on one or both sides. Hydronephrosis can be mild to severe.
What does hydronephrosis look like on imaging?
Hydronephrosis on Ultrasound
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.
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.
Hydronephrosis on CT scan
Hydronephrosis is often diagnosed on CT. We see a dilated collecting system of the kidney. This is located inside the kidney and becomes dilated or swollen.
An advantage of CT is that we can often diagnose the cause of the blockage. We can often see stones, tumors and other causes of urinary outflow blockage.
Hydronephrosis on MRI
Hydronephrosis can be seen on abdominal MRIs. We can not tell the cause of the hydronephrosis because MRI does not show stones well. MRI also usually images the abdomen only so we may not see the cause of the hydronephrosis and blockage if it’s in the pelvis.
Hydronephrosis on Nuclear Medicine
Nuclear medicine renal scans are often ordered to evaluate hydronephrosis. The nuclear scans can tell us if the hydronephrosis is from a significant blockage of the kidney which is causing the urine to back up.
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 can often be seen on CT.
Hydronephrosis is most common from a stone which passes from the kidney. The stone will block the ureter causing a backup of urine into the kidney. 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 strictures 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. This causes a backup of urine and hydronephrosis.
Infections of the urinary tract can cause the appearance of hydronephrosis. We can not see a clear cause of the hydronephrosis on imaging. Laboratory testing of the urine and is often needed to diagnose a urinary tract infection.
Hydronephrosis can also be seen on both kidneys when someone can’t urinate. This is seen most common when there is a large prostate in older men. This can cause difficulties with urination and is called bladder outlet obstruction. Other causes can be from an obstruction of the urethra (where urine passes from the bladder).
Additional common cause of hydronephrosis is when there is a mass or cancer blocking the ureter or bladder. For example, a cancer of the bladder where the ureter enters may cause an obstruction and hydronephrosis of the kidney. A mass of the ovary can press on the ureter and cause obstruction. Any mass that presses on the ureter can cause obstruction and hydronephrosis.
Other causes can include a narrowing or mass where the kidney meets the urethra called a UPJ obstruction. A portion of the kidney collecting system can protrude outside the kidney (extrarenal pelvis) and look like hydronephrosis.
Is hydronephrosis dangerous? (or cancerous)
It can be when the hydronephrosis is from a severe blockage. This can cause the kidney function to deteriorate.
Hydronephrosis can also occur when a cancer blocks the kidney outflow. This can be anywhere along the urinary tract.
Is an ultrasound test enough for hydronephrosis?
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.
What is one of the more common causes of hydronephrosis?
One of the most common causes of hydronephrosis is when someone is passing a kidney stone. This occurs when a kidney stone passes into the ureter and causes blockage of urine flow. Usually this will be associated with pain and blood in the urine. Often a CT scan will show a dilated collecting system of the kidney on one side which indicates blockage related to the passing stone.
What else can look like hydronephrosis?
There are mimickers of hydronephrosis as well. For example, a patient can have cysts along the collecting system in the kidney called parapelvic cysts which can look like hydronephrosis.
When the bladder is full, this can cause a urine backup and appearance of hydronephrosis.
Sometimes there is hydronephrosis after a blockage has been relieved which never goes away.
How do we know if hydronephrosis is from a blockage or something else?
The big concern with a blocked kidney that if untreated is loss of kidney function. Sometimes your doctor will order a nuclear medicine kidney scan to distinguish between a blockage of the kidney and one that simply looks like one. A CT scan will often show a cause of the blockage.
How is hydronephrosis treated?
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.
What type of doctor treats hydronephrosis?
Many primary care doctors and specialists may be involved in the diagnosis of hydronephrosis. Often a urology doctor will be involved in the management of hydronephrosis. A urologist specializes in diagnosing and treating diseases of the urinary tract.
Hydronephrosis is a swelling or dilation of the kidney collecting system. This occurs from backup or reflux of urine from the bladder. Treatment will be directed towards the cause of the hydronephrosis. Blockage of the urinary tract is a common cause of hydronephrosis. Treatment will be aimed at relieving the blockage. A urology specialist will often be involved in the treatment of hydronephrosis.