Hydronephrosis

What hydronephrosis is

Each kidney collects urine in a central funnel (the renal pelvis), which drains through a tube (ureter) to the bladder. If urine cannot flow, pressure builds and the collecting system stretches. When the ureter is also dilated, it is called hydroureteronephrosis.

Causes

In adults

In babies and children

• Prenatal hydronephrosis: found on 1 to 2% of pregnancy ultrasounds. Most cases are mild and resolve on their own.
• Ureteropelvic junction (UPJ) obstruction: narrowing where the kidney joins the ureter.
• Vesicoureteral reflux: urine flows backward from the bladder to the kidneys.
• Posterior urethral valves: in boys, a blockage in the urethra causing hydronephrosis in both kidneys.
• Ureterocele and other structural differences.

Symptoms

Symptoms depend on how quickly the blockage develops:

• Sudden blockage: severe, colicky pain in the side or back (flank) that may spread to the groin, nausea and vomiting, blood in the urine.
• Gradual blockage: often no symptoms, or a dull ache in the side.
• Urinary symptoms: urgency, frequency, weak stream, incomplete emptying, reduced urine.
• Infection: fever, chills and burning when urinating. A kidney infection behind a blockage can quickly cause sepsis.
• Babies: usually no symptoms; sometimes urinary infections, poor growth.

Grades of hydronephrosis

Hydronephrosis is graded by how dilated the kidney appears on ultrasound:

The grade does not always reflect how blocked the kidney is; functional tests help decide.

Diagnosis

• Ultrasound: the first test; shows swelling and sometimes stones.
• Urine and blood tests: infection, blood, kidney function (creatinine, eGFR).
• CT scan: finds stones, tumors and the level of blockage.
• MAG3 renal scan (diuretic renography): measures how well each kidney works and whether drainage is truly obstructed.
• Voiding cystourethrogram (VCUG): in children, to check for reflux and urethral valves.
• Bladder scan for retained urine; cystoscopy to look inside the bladder.

Treatment

Treatment aims to relieve pressure, protect kidney function and fix the cause.

Relieving the blockage

• Urinary catheter: for bladder outlet blockage.
• Ureteral stent: a thin tube placed through the bladder to hold the ureter open.
• Nephrostomy: a tube through the back into the kidney, often used for infected obstruction.

Treating the cause

• Stones: many small stones pass with pain relief and medicines that relax the ureter. Larger ones need shock wave lithotripsy, ureteroscopy or surgery.
• Prostate enlargement: medicines or surgery.
• Strictures and UPJ obstruction: pyeloplasty (surgical reconstruction), often robotic.
• Tumors: cancer treatment, often with a stent or nephrostomy to protect the kidney.
• Pregnancy: usually no treatment; pain relief and occasionally a stent.
• Babies: most mild cases are monitored with ultrasound; some receive preventive antibiotics; surgery for significant obstruction.

Complications

• urinary infections and sepsis
• loss of kidney function, which can be permanent if blockage persists for weeks
• chronic kidney disease if both kidneys are affected
• high blood pressure

Frequently asked questions

What is hydronephrosis?

Hydronephrosis is swelling of the kidney caused by urine that cannot drain properly. It happens when something blocks urine flow, such as a stone, enlarged prostate or narrowing, or when urine flows backward from the bladder. It is a sign of an underlying problem.

Is mild hydronephrosis serious?

Mild hydronephrosis is often not serious, especially in pregnancy or in babies, where it frequently resolves on its own. It still needs follow-up to make sure it does not worsen and to find the cause. Pain, fever or reduced kidney function make it more urgent.

What are the symptoms of hydronephrosis?

Sudden hydronephrosis causes severe pain in the side or back, often spreading to the groin, nausea and vomiting, and sometimes blood in the urine. Slowly developing hydronephrosis may cause no symptoms or a dull ache. Fever suggests infection.

Can hydronephrosis go away on its own?

Yes, when the cause resolves, such as when a small stone passes, after pregnancy, or as a baby grows. Persistent blockages need treatment to protect the kidney. Your doctor will monitor with ultrasound and kidney function tests.

Is hydronephrosis common in pregnancy?

Yes. Mild hydronephrosis, usually of the right kidney, is very common in pregnancy because hormones relax the ureters and the uterus presses on them. It usually needs no treatment and resolves after delivery, unless it causes severe pain or infection.