NephrologyTier 2Disease (DEADMAN)

Obstructive uropathy

Description

Structural or functional blockage of urine flow anywhere from the renal pelvis to the urethra, causing back-pressure (hydronephrosis) and, if prolonged, renal parenchymal injury
Can be unilateral (often asymptomatic if the other kidney is normal) or bilateral/single-kidney (causes AKI - "post-renal" failure)

Causes vary by age/sex: children - congenital (PUJ obstruction, posterior urethral valves); young/middle-aged adults - stones; older men - benign prostatic hyperplasia; any age - malignancy (pelvic/retroperitoneal tumours, lymphadenopathy)

Obstruction -> raised intraluminal/intratubular pressure transmitted back to the nephron -> reduced GFR, tubular injury, and (if prolonged) interstitial fibrosis
Intrinsic causes: stones, strictures, tumours (renal pelvis/ureteric/bladder), blood clot
Extrinsic causes: BPH/prostate cancer (the most common cause of obstruction overall), pelvic malignancy, retroperitoneal fibrosis, pregnancy (physiological, usually right-sided)

Renal tract ultrasound - first-line, detects hydronephrosis/hydroureter; may be falsely negative very early or with a retroperitoneal-encased ureter (fibrosis)
CT KUB (non-contrast) - defines the level and cause, especially for stones
Bloods: renal function (may be normal with unilateral obstruction and a healthy contralateral kidney)

Relieve the obstruction - level-dependent: urethral/bladder catheter (lower tract), ureteric stent or percutaneous nephrostomy (upper tract)
Post-obstructive diuresis - a large, sodium/water-rich diuresis can follow relief of chronic bilateral obstruction - monitor fluid balance and electrolytes closely, especially after prolonged obstruction
Treat the underlying cause once decompressed (stone removal, prostate management, tumour treatment)
Infected obstruction is a urological emergency - decompress urgently, do not delay for definitive stone/cause treatment

Benign prostatic hyperplasia, pelvic/retroperitoneal malignancy, nephrolithiasis, pregnancy, retroperitoneal fibrosis

Reversibility depends on duration - renal function recovers well if obstruction is relieved within days-weeks; prolonged obstruction (many weeks) causes irreversible fibrosis and permanent function loss
Unilateral obstruction can silently destroy a kidney with normal overall renal function (compensated by the contralateral kidney) - a trap for missed diagnosis

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