Definition
Hydronephrosis is dilatation of the renal pelvis and calyces, usually caused by obstruction to urine flow (occasionally by reflux). Sustained obstruction threatens renal function, so prompt relief matters.
Causes
Unilateral (PACT): Pelvi-ureteric junction obstruction, Aberrant renal vessels, Calculi, Tumours of the renal pelvis or ureter.
Bilateral (SUPER): Stenosis of the urethra, Urethral valves, Prostatic enlargement, Extensive bladder tumour, Retroperitoneal fibrosis.
Clinical presentation
- May be asymptomatic, or cause loin pain and features of the underlying cause
- Acute kidney injury if bilateral (or affecting a single functioning kidney)
- Symptoms of the cause — colic (stones), poor stream (prostate)
Investigations
- Renal ultrasound — first-line to confirm dilatation and assess the bladder
- CT (CT KUB for stones) to define the level and cause
- Bloods for renal function; consider functional imaging where relevant
Management
- Relieve the obstruction: nephrostomy or ureteric stent for upper-tract obstruction; catheterisation for bladder outflow obstruction
- Treat the cause (stone removal, prostate management, tumour treatment)
- Monitor for post-obstructive diuresis after decompression (fluid and electrolyte losses)
MRCP-specific traps
- Bilateral hydronephrosis implies an obstruction at or below the bladder — think prostate or a pelvic process.
- Relieve obstruction promptly to preserve renal function; anticipate a post-obstructive diuresis.
Summary
Hydronephrosis is dilatation of the collecting system, usually obstructive (unilateral: PACT; bilateral: SUPER). Confirm on ultrasound, define the cause on CT, relieve obstruction with a nephrostomy, stent or catheter, and watch for a post-obstructive diuresis.
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