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Causes of Hydronephrosis

If only one of your ureters or kidneys becomes blocked then you will experience unilateral hydronephrosis - affecting only one kidney. This commonly results from a blockage at the point where the wide urine-collecting system of each kidney (the renal pelvis) joins the narrow tube of the ureter.

Causes of this type of blockage include:

  • your kidney developing incorrectly so that the ureter joins the kidney at too high a point,
  • a kink forming at the point where the ureter meets the kidney because one of your kidneys has shifted downwards,
  • a kidney stone,
  • the ureter being squeezed by an artery or vein that is in an abnormal position, and
  • a tumour in your kidney.

Unilateral hydronephrosis can also result from a blockage in one of your ureters.

Causes of this type of blockage include:

  • a stone in the ureter,
  • a tumour in the ureter, or near the ureter and putting pressure onto it,
  • a narrowing of the ureter resulting from an injury, infection, surgery, or birth defect, and
  • a disorder of the nerves or muscles in the ureter.

If the urine flow is blocked at your bladder then the blocked urine will apply pressure to both kidneys equally. In this case you can suffer bilateral hydronephrosis – affecting both kidneys.

Causes of this type of hydronephrosis include:

  • a urinary stone,
  • a blood clot,
  • a tumour in the bladder
  • your bladder becoming inflamed or pressed upon by something else within your abdomen,
  • a disorder of the nerves or muscles in the bladder,
  • bulging of the lower end of the ureter into the bladder (ureterocele),
  • cancer of the bladder, prostate or other organs in the pelvis, and
  • enlargement of the prostate gland.

Hydronephrosis of both kidneys can occur during pregnancy if the uterus enlarges so that it squeezes the ureters. This form of hydronephrosis usually resolves when the pregnancy ends.