Obstruction of the urinary tract can occur at any point from the calyces to the external urethral meatus. Obstruction within the urinary tract is best divided into upper tract and lower tract obstruction. Obstruction can be acute or chronic. Acute upper tract obstruction is most commonly due to a calculus and acute lower tract obstruction in men is often due to benign prostatic enlargement. Chronic upper tract obstruction in the Western world is most commonly due to calculi or pelvi-ureteric junction obstruction. Chronic lower tract obstruction in men will again be due to benign prostatic enlargement in a majority of cases.
In upper tract obstruction imaging is the cornerstone of investigation. The most commonly used radiological investigation being a stone protocol non-contrast computed tomography scan of kidneys, ureters and bladder (NCCT–KUB). Acute and chronic lower tract obstruction is often treated in the initial stages by the passage of a urethral catheter. Chronic lower tract obstruction can be high or low pressure. High-pressure chronic retention is potentially fatal due to renal failure and therefore monitoring of fluid status and serum electrolytes is essential. The initial treatment for obstruction is dependent on the presence or absence of renal impairment and sepsis. If either of these is present then some form of upper tract decompression may be warranted, either in the form of percutaneous nephrostomy tubes or JJ stents.
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