Hydronephrosis refers to the dilatation of the renal pelvis and calyces of the kidney.

Hydronephrosis =

  1. Obstruction of the urinary tract or
  2. Reflux of urine from the bladder up to the kidney.


Upper tract Lower Tract
UPJ obstruction BPH
Stones Prostate cancer
Tumours Posterior urethral valves
UVJ obstruction Reflux


  • UPJ and UVJ obstruction are congenital stenotic lesions
  • Stones and tumours can occur anywhere along the ureter
  • A ureterocoele is a cystic ballooning of the distal ureter as is it enters the bladder
  • Extrinsic obstructions of the ureter include conditions like pregnancy, tumours and retroperitoneal fibrosis

Patients with stones usually present with typical renal colic.

UVJ obstruction usually present in childhood while UPJ can be asymptomatic until later in life. They may present with pyelonephritis or flank pain, or the hydronephrosis may be an incidental radiographic finding.

UVJ obstructions can be distinguished from UPJ obstructions in that the ureter is also dilated - hydroureteronephrosis.

UPJ obstruction are usually corrected with pyeloplasty while UVJ obstructions may require re-implantation of the ureter into the bladder.

Lower urinary tract obstructions can cause hydronephrosis from increased back pressure. The commonest causes in older patients include BPH and prostate cancer. In baby boys posterior urethral valves are most common. These can be endoscopically ablated and have good results if picked up early enough.

Hydronephrosis can also be secondary to vesicoureteral reflux without any obstruction. As the bladder fills and/or as the patient voids urine refluxes back up the ureters to variable heights. The ureterovesical junction in these children has not developed its protective antireflux mechanism. Urine becomes stagnant in the bladder as a fixed amount continues to reflux with each void. This urine can become infected and can lead to pyelonephritis. Most patients present with UTIs although some may be asymptomatic with hydronephrosis. Pyelonephritis in children can cause irreversible scarring and damage to the developing kidney. If not treated early, permanent renal damage can occur.

The diagnosis is made with a voiding cystourethrogram - VCUG. For low grade reflux treatment consists of long term prophylactic antibiotics (usually TMP-SMX). Follow up ultrasound are needed every 6 to 12 months to ensure that the kidneys are growing well and that no parenchymal scarring is occurring. Fortunately, the anti-reflux mechanism will develop in most of these children as they grow. If patients have high grade reflux, if they continue to have infections despite antibiotics or if the degree of reflux gets worse then surgery is needed. This involves re-implantation of the affected ureter into the bladder in such a way as to recreate the physiological valve.

Contents by Dr Íomhar O' Sullivan 10/05/2005. ÍOS 26/05/2006. Last review Dr ÍOS 13/12/21.