Renal and Perinephric Abscess
A renal (or perinephric) abscess is a walled collection of pus in or around the kidney — suspected when pyelonephritis fails to improve, confirmed on CT, and treated with antibiotics plus drainage of larger collections, escalating to surgery if drainage fails.
The big picture
A renal abscess is a localised collection of pus within the renal parenchyma; a perinephric abscess lies in the perinephric space (often from rupture of a renal abscess or extension of pyelonephritis). They arise from ascending infection (often with obstruction/stones) or, less commonly, haematogenous seeding. Risk factors include diabetes, obstruction/stones, and immunosuppression.
Pyelonephritis not improving = image for an abscess; antibiotics for all, drain larger/non-resolving collections, relieve obstruction, and escalate to surgery if drainage fails.
Symptom sorter
The common presentation.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Treatment ladder
Antibiotics for all, with percutaneous drainage of larger or non-resolving collections and relief of obstruction; escalate to surgery if these fail.
Procedure chooser
- Open drainage if percutaneous fails; nephrectomy for a destroyed kidney or extensive disease
Complications
- Sepsis, perinephric extension, fistula, renal loss
- Drain-related complications; surgery risks
- Image non-resolving pyelonephritis; drain larger collections; relieve obstruction
- Drainage/surgery; treat obstruction/stones
Follow-up
- Clinical/biochemical response (fever, CRP)
- Collection resolution on imaging
- Renal function; underlying obstruction/stones
- Reassess response over days; repeat imaging if not improving
- Sepsis resolves and the collection shrinks/resolves
- Persistent sepsis/collection — drain or escalate
- Failure to improve; to confirm resolution
- Recurrence if obstruction/stones untreated; renal scarring
If treatment fails
If the patient isn't improving, ask: is the collection adequately drained, is there untreated obstruction, and are the antibiotics appropriate?
Red flags
Image for a renal/perinephric abscess (contrast CT).
Add drainage to antibiotics — don't rely on antibiotics alone.
Relieve the obstruction as well as draining the abscess.
Summary tables
Renal/perinephric abscess essentials
| Item | Detail |
|---|---|
| Clue | Pyelonephritis not improving / flank mass |
| Confirm | Contrast CT |
| All patients | Antibiotics (after cultures) |
| Larger/non-resolving | Percutaneous drainage; relieve obstruction |
| If drainage fails | Open drainage / nephrectomy |
Memory hooks
Pyelonephritis not improving → think abscess → CT.
Antibiotics for all; drain the larger ones.
Relieve any obstruction.
Drainage fails → surgery/nephrectomy.
Board traps
Non-resolving pyelonephritis → abscess (image with CT).
Larger collections need drainage.
Treat associated obstruction.
Clinical cases
A diabetic man treated for pyelonephritis remains febrile after several days of appropriate antibiotics. Contrast CT shows a 5 cm intrarenal abscess.
What is the management?