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.

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