Hydronephrosis is when one or both kidneys swell with backed up urine. This swelling can lead to kidney damage.

Hydronephrosis is not a condition but a symptoms of another condition.

Urinary Tract System
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Hydronephrosis is caused by urinary tract problems that makes it difficult for urine to leave the kidneys. Urine may be slowed or blocked by:

  • A birth defect that causes a narrowing of the tube that leads from the kidney to the bladder
  • Kidney stones
  • Blood clots
  • Tumors
  • Scar tissue or injury to the urinary tract

Kidney, Ureter, Bladder, and Kidney Stone
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Other conditions that may cause problems with urine flow include:

  • Reflux—urine to flows back into the kidneys from the bladder
  • Abnormal bladder function due to problems with the nerves

In most cases, the child is born with one of these conditions that affect the urinary tract. For some, the condition develops later on.