The causes of hydronephrosis are many and depend a lot on a person’s age, health history, and body structure. Hydronephrosis happens when urine cannot flow normally from the kidney to the bladder. This blockage causes urine to build up and the kidney to swell. Knowing the causes of hydronephrosis is key to choosing the right treatment because the condition usually happens because of another problem in the urinary system or nearby areas.
Causes can be from physical blockages, nerve or muscle problems, or pressure from outside the urinary tract. Some causes are present from birth, while others develop later due to infections, injuries, or illness. Finding the cause quickly helps stop lasting kidney damage.
Congenital Causes
Some people are born with changes in their urinary system that cause hydronephrosis. These are often found before birth or soon after.
- Ureteropelvic Junction (UPJ) Obstruction: This common problem happens when the connection between the kidney and the ureter is too narrow or blocked. It stops urine from flowing properly.
- Posterior Urethral Valves (PUV): This affects baby boys and involves extra flaps of tissue in the urethra that block urine flow, causing pressure on the kidneys.
- Vesicoureteral Reflux (VUR): Urine flows backward from the bladder into the ureters and kidneys, raising pressure and infection risk.
Some of these birth defects may get better on their own, need monitoring, or require surgery depending on how bad they are.
Kidney Stones
Kidney stones are a common cause of hydronephrosis in adults. These hard lumps made of minerals can get stuck in the ureters and block urine flow.
- The blockage might be partial or full, causing different levels of swelling.
- Stones often cause severe pain in the side (flank), blood in urine, and urgent or frequent urination.
- Treatment depends on the stone size and place, and may include medicines, shock wave therapy, or surgery.
Treating stones fast is important to avoid long-term kidney pressure and damage.
Ureteral Strictures and Scarring
A ureteral stricture means the tube carrying urine from the kidney to the bladder has narrowed. This can happen because of:
- Infections like tuberculosis or schistosomiasis that cause scarring.
- Past surgeries or radiation treatments that injure the ureters.
- Scar tissue tightening the ureter and blocking urine flow.
Doctors often treat strictures with techniques like stretching the ureter, placing a stent, or surgery to fix the damage.
Tumours and External Compression
Tumours or growths can block urine flow by growing inside the urinary tract or pressing on it from outside.
- Cancers of the bladder, prostate, or cervix often cause blockage.
- Retroperitoneal fibrosis is a rare condition where fibrous tissue forms behind the abdomen and presses the ureters.
- Swollen lymph nodes from cancers like lymphoma can also push on the ureters.
Hydronephrosis from tumours is often a sign of a more serious illness. Scans and biopsies help confirm diagnosis and guide care.
Pregnancy
Pregnancy commonly causes temporary hydronephrosis because of:
- Hormone changes, especially progesterone, which relax the ureter muscles and slow urine flow.
- The growing uterus pressing on the ureters, often on the right side.
This type usually goes away after birth. Doctors watch closely to avoid infections or other problems, treating only if symptoms appear.
Neurological and Functional Disorders
Some hydronephrosis cases happen without a physical blockage, due to bladder problems affecting urine flow.
- Conditions like spinal cord injury, multiple sclerosis, or diabetes can damage nerves that control urination (neurogenic bladder).
- Enlarged prostate or urethral narrowing in older men can block urine leaving the bladder.
- When the bladder does not empty well, pressure backs up to the kidneys.
Fixing the nerve or bladder problem is important to treat this kind of hydronephrosis.
Infections and Inflammation
Repeated or bad urinary infections can cause or worsen hydronephrosis, especially if anatomy is abnormal.
- Long-lasting kidney infections (chronic pyelonephritis) cause swelling and scarring that narrow the ureters.
- Other conditions like interstitial cystitis or endometriosis in women can block urine flow.
- Rare infections, such as fungal or parasitic diseases, may also cause obstruction.
Treating infections quickly helps prevent more damage and hydronephrosis.
Post-Surgical or Traumatic Injury
Hydronephrosis can develop after surgery or injury to the abdomen or pelvis.
- Ureters may get injured accidentally during surgeries like hysterectomy or bowel removal, causing blockages or leaks.
- Blunt injuries can bruise or swell urinary structures.
- Swelling or blood clots after surgery may block urine flow temporarily and might need stents or catheters.
Post-surgery hydronephrosis often gets better but needs early detection to avoid lasting harm.
Summary
The causes of hydronephrosis cover a wide range of physical, functional, infection-related, and systemic problems. From birth defects in babies to kidney stones and tumours in adults, causes vary by age and gender. Finding the exact reason for urine blockage or poor flow is key to choosing the right treatment. Often, imaging and lab tests help find the cause, while some cases need care from different specialists.
Knowing the cause improves the chance of recovery and helps stop the problem from returning or harming the kidneys. The next step is to understand the symptoms of hydronephrosis, which can differ depending on how fast and severe the condition is.
