What to Know About Hydronephrosis

Medically Reviewed by Sanjay Ponkshe on July 13, 2023
3 min read

Hydronephrosis happens when your kidneys swell up because you cannot pass urine through your urinary tract. It may affect one or both kidneys, and it can occur in people of all ages. 

Your urinary tract is composed of your kidneys, your bladder, your ureters, and your urethra, and it’s a primary means to remove excess fluid and waste from your body. Your kidneys are instrumental in filtering your blood, and your ureters are tubes that connect your kidneys to your bladder, and they’re how urine passes from the kidneys to the bladder. Issues at any point along the urinary tract can lead to hydronephrosis.

In many cases, hydronephrosis has no clear cause. When there is a known cause, it’s either obstruction, where urine cannot leave the bladder because the urinary tract has been blocked, or reflux, when urine flows backwards into the kidney due to muscular issues. 

Obstruction may occur at any point along the urinary tract, like when a ureter swells and blocks the flow of urine into the bladder, or a kidney stone blocks the urethra.

In children, over half of hydronephrosis cases have unknown causes, and the condition clears up on its own. Very rarely, a child may be born with a ureter that has not connected to the bladder in the normal location, which is treatable with surgery.

Adults. In adults, a range of conditions can cause hydronephrosis. These can include: 

  • Kidney stones that block the urinary tract or kidneys.
  • Blood clots in the kidney or bladder.
  • Nerve or muscle problems that affect the kidneys or ureters.
  • Tumors growing on organs that are near or part of the urinary tract.
  • Vesicoureteral reflux, which, in the same way as children, can cause urine to build up in the kidneys.
  • Benign prostatic hypertrophy (BPH), an enlargement of the prostate that can put pressure on the urethra.
  • Narrowing of the urinary tract due to injury, surgery, birth defect, or a birth defect.
  • A bulge in the ureter, also known as a ureterocele
  • An inability to empty the bladder, called urinary retention.

Pregnancy. During pregnancy, your uterus expands and can press on one or both ureters, blocking the flow of urine from the kidneys. Hydronephrosis can also be caused by uterine prolapse, a non-life-threatening condition in which your uterus moves out of its normal position. Hydronephrosis can also be caused by the wall between your vagina and bladder weakening, allowing your bladder to sag into your vagina.

You may not feel any symptoms of hydronephrosis ⁠— many patients don’t. If you do, they may include:

Your health care provider will talk to you about your symptoms and perform a physical exam. They may order a set of blood or urine tests to determine your kidney function. You may also receive x-rays, MRIs, ultrasounds, or CT scans to get a better look inside your body.

If it doesn’t clear up on its own, hydronephrosis is treated by addressing the underlying cause. A doctor or surgeon may drain the built-up urine, with a catheter in your urethra or a stent in your ureter. to prevent kidney damage. the obstruction is caused by a kidney stone, you’ll need to pass the stone or have it removed. If it’s being caused by an infection, the infection will be treated with a round of antibiotics.

You may be asked to stay in the hospital for observation or further testing after any procedure.

The most common complication of hydronephrosis is a urinary tract infection. It’s also possible to contract a kidney infection, which is a serious ⁠— but treatable ⁠— condition. When a chronic obstruction is finally relieved, you might experience post-obstructive diuresis, a condition in which you urinate excessively.

If you notice any irregularities in the way you urinate, whether it’s painful to urinate or you’re urinating infrequently, you should talk to a doctor. If you cannot urinate, you need immediate medical help ⁠— go to the doctor right away.