Renal & Urology

Hydronephrosis

Hydronephrosis is dilatation of the renal collecting system, usually caused by impaired urine drainage; localise the cause, protect renal function, and treat an infected obstructed kidney as a urological emergency.

In a nutshell

Hydronephrosis is dilatation of the collecting system, usually from impaired urine drainage. Find the cause and level; use urgent ultrasound when obstruction or pyonephrosis is possible. Fever/sepsis with obstruction, an obstructed solitary kidney, bilateral obstruction or obstructive AKI needs immediate urology and drainage. Treat the cause after decompression, and monitor renal recovery and post-obstructive diuresis. Antenatal disease usually follows a paediatric surveillance pathway.

Classic presentation

A patient with flank pain and hydronephrosis from a ureteric stone, or an older man with retention, bilateral hydronephrosis and acute kidney injury. Fever and rigors in either presentation mean infected obstruction until proven otherwise.

Key points

Hydronephrosis is a radiological sign; establish whether obstruction is present and where it is.
In AKI, suspected pyonephrosis needs ultrasound within 6 hours; obstruction risk or an unexplained AKI needs urgent ultrasound within 24 hours.
Pyonephrosis, an obstructed solitary kidney, bilateral upper-tract obstruction or obstructive AKI requires immediate urology referral.
Decompress an upper-tract obstruction with a specialist-selected stent or nephrostomy; catheterise significant bladder-outlet obstruction.
After drainage, monitor for post-obstructive diuresis, electrolyte loss and incomplete renal recovery.
Antenatal hydronephrosis is often transient; use postnatal ultrasound and specialist-led imaging/follow-up rather than automatic surgery.

First-line investigation

Clinical assessment, urinalysis/U&E and renal-tract ultrasound; CT or specialist functional imaging is selected according to the suspected cause and age/pregnancy.

Management

Recognise infected or high-risk obstruction

Sepsis with hydronephrosis, an obstructed solitary kidney, bilateral upper-tract obstruction or obstructive AKI requires immediate urology referral and source-control planning.^2,6

Image and decompress

Use renal-tract ultrasound urgently when obstruction or pyonephrosis is possible; drain the upper tract with a specialist-selected stent/nephrostomy or drain lower-tract retention with catheterisation.^2,1,4

Treat the cause

Use the current stone pathway for suspected renal colic, and specialist treatment for PUJ/ureteric, outlet, reflux or malignant obstruction.^5,9,8

Protect renal function

Monitor urine output, fluid balance, renal function and electrolytes after relief; arrange paediatric or adult urology follow-up to confirm drainage and renal recovery.^11,10,2

Exam traps

Antibiotics do not replace drainage in an infected obstructed system.
Normal unilateral renal function does not exclude important obstruction or future renal damage.
Bilateral dilatation often points to lower-tract obstruction, but localisation still requires imaging and clinical assessment.
Do not use adult CT or catheter rules automatically in children or pregnancy.
Expect post-obstructive diuresis after relief of significant obstruction and monitor electrolytes.

Illustrations

Hydronephrosis on renal ultrasoundA renal ultrasound image showing a dilated, anechoic pelvicalyceal system (ballooned renal pelvis and blunted calyces) within the kidney.Cerevisae, Wikimedia Commons · CC-BY-SA-4.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.