Hydronephrosis

Hydronephrosis is swelling (dilation) of the urine-collecting structures of one or both kidneys due to obstruction of urine flow from the kidney. This can impair kidney function. Hydronephrosis isn't a specific disease, but a sign of an underlying problem. Causes include:

• Blockage of the urinary system present at birth (congenital)
• A kidney or ureteral stone (nephrolithiasis)
• A blood clot
• Scarring of the ureter, usually from injury, radiation therapy or previous surgery
• A tumor in or around the ureter
• Prostate gland enlargement (benign prostatic hyperplasia)
• Pregnancy

Hydronephrosis may develop suddenly — due to, for example, passing a kidney stone — and cause severe pain in the back, lower abdomen and groin on the side of the blockage. It may also develop so gradually over weeks or months — due to, for example, a slow-growing tumor — that it causes no symptoms. Urine output usually remains normal as long as one kidney functions properly.

A doctor can confirm a diagnosis of hydronephrosis by:

• X-rays of the kidneys, such as dye studies (excretory urogram)
• Computerized tomography (CT)
• Ultrasound
• Magnetic resonance imaging (MRI)
• Cystoscopy and catheterization of the ureter with dye injection

Treatment depends on the cause and the severity of the obstruction. Some blockages, such as from blood clots or a kidney stone, can resolve without treatment. Surgery may be necessary to relieve the blockage. Rarely, surgical removal of the kidney may be required.