Hydronephrosis: What Causes Urine To Accumulate In the Kidneys?

What Is Hydronephrosis?

urinary tract blockage

Hydronephrosis refers to an accumulation of urine in the kidneys, which causes one or both kidneys to swell. The condition is caused by a partial or complete blockage in the urinary tract, preventing urine from exiting the body normally. This accumulation of urine in the kidneys can become serious if not treated promptly. Hydronephrosis is very common, with over 200,000 new cases diagnosed in the US every year.


  • Kidney stones
  • Congenital defect
  • Blood clots
  • Scar tissue from a previous surgery or injury
  • Tumors in the bladder, cervix or colon or prostate
  • Enlarged prostate
  • Pregnancy
  • Urinary tract infection
  • Inflammation in the urethra or urinary tract


Hydronephrosis is categorized into grades by the degree of renal pelvic dilation. Grades range from Grade 0 (no measurable dilation) to Grade 4 (severe dilation).


  • Pain in the abdomen
  • Pain in the back
  • Pain in the flank
  • Nausea
  • Vomiting
  • Sweating
  • Painful urination
  • Inability to urinate
  • Feeling of incomplete urination
  • Fever



If hydronephrosis has been gradually developing, you may notice the symptoms early on. In this case, your primary care physician may be able to diagnose the condition and refer you to a urologist for treatment. If the hydronephrosis is acute and develops rapidly, symptoms will typically come very quickly and result in diagnosis at an emergency facility.


Treating hydronephrosis depends on the cause. Mild cases caused by urinary tract infections can be treated with a course of antibiotics. Hydronephrosis caused by a blockage in the urinary tract, such as a tumor or kidney stone often need surgical intervention to remove the blockage and restore normal urinary flow.

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