Obstruction of the urinary tract causes urinary stasis and back pressure in the tract – this may lead to infection, calculus formation and renal failure. It is caused by an anatomical lesion or a neuromuscular defect. Obstruction may occur at any level:

Lesions above the bladder present with renal colic if the onset is sudden, aching loin pain if gradual, or (commonly) with no symptoms. Prior symptoms of bladder dysfunction (neurological, obstruction to outflow) may give an important clue.

Infection is common and causes malaise, fever, dysuria and sometimes haematuria. Partial obstruction may result in paradoxical polyuria.

Complete obstruction causes complete anuria.


Renal function will only be severely altered if obstruction affects both kidneys (or a single functioning kidney). Rectal/vaginal examination may reveal enlarged prostate or pelvic tumour. Ultrasound detects dilatation of bladder and collecting system of the kidneys. Bladder, urethral and lower ureter lesions may be shown by cytoscopy, but CT scanning or MRI, and antegrade or retrograde pyelography, are often required if obstruction affects ureters. Urine cultures should always be performed.


The aim is to remove the obstruction, but temporary relief by catheter drainage (e.g. nephrostomy) is often necessary first.  Infection should be treated.  Infection above an obstruction requires urgent drainage.  Post-obstructive diuresis may require IV fluid replacement.

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