Hydronephrosis
Hydronephrosis is dilation of the collecting system — and the central lesson is that dilation does not always mean obstruction; you must prove obstruction and protect function.
The big picture
A dilated pelvicalyceal system has many causes: true obstruction (stone, stricture, tumour, UPJ), but also non-obstructive states (reflux, high flow, a baggy post-obstructive system, pregnancy). Ultrasound shows the dilation; it does not prove obstruction.
Dilation ≠ obstruction — prove it (renogram), grade urgency (infection/AKI/single kidney), and decompress when the kidney or patient is threatened.
Red flags
Infected obstructed kidney — urgent decompression.
Total function at stake — act early.
Relieve obstruction urgently.
Symptom sorter
Flow is genuinely blocked.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Treatment ladder
Treat proven obstruction and protect renal function; decompress urgently when infected, in a single kidney, or with deteriorating function.
Complications
- Renal impairment from sustained obstruction
- Pyonephrosis/sepsis if infected
- Stone/infection in stagnant systems
- Stent/nephrostomy complications
- Post-obstructive diuresis
- Prove obstruction before intervening
- Decompress infected obstruction promptly
- Decompress emergencies
- Replace post-obstructive losses
- Treat the underlying cause
Summary tables
Obstructive vs non-obstructive dilation
| Feature | Obstructive | Non-obstructive |
|---|---|---|
| Renogram drainage | Impaired | Normal |
| Causes | Stone, stricture, tumour, UPJ | Reflux, high flow, pregnancy |
| Function risk | Yes (especially acute) | Usually low |
| Action | Relieve / decompress if threatened | Observe / treat cause |
Memory hooks
Dilation ≠ obstruction.
US shows it; renogram proves it.
Acute high-pressure obstruction is an emergency.
Fever + obstruction → drain.
Expect post-obstructive diuresis after relief.
Board traps
Bilateral hydronephrosis in pregnancy assumed pathological — often physiological.
Dilated system drained without proving obstruction.
Septic obstructed kidney delayed for elective work-up.
Clinical cases
An asymptomatic patient has unilateral hydronephrosis on ultrasound with normal renal function and no stone on CT.
What test determines whether this needs intervention?