Related Subjects:
|Pyelonephritis and Urosepsis (UTI)
|Pyonephrosis
|Perinephric abscess
|Acute Kidney Injury (AKI) / Acute Renal Failure
|Renal/Kidney Physiology
|Chronic Kidney Disease (CKD)
⚠️ Suspect a perinephric abscess if a patient remains febrile after 4–5 days of adequate antibiotic therapy for pyelonephritis.
Definition
- 💉 Collection of pus in the perinephric space (between renal capsule and Gerota's fascia) as a complication of UTI or haematogenous seeding.
Pathophysiology
- Abscess forms within the perinephric space bounded by Gerota's fascia.
- May extend inferiorly into the psoas muscle and pelvis.
- Can arise from: (1) ascending infection from lower urinary tract, (2) direct extension from renal parenchymal infection, or (3) haematogenous spread from distant focus.
Causative Organisms
- Gram-negative bacteria (most common): E. coli, Klebsiella pneumoniae, Proteus species.
- Staphylococcus aureus: Particularly with haematogenous spread (e.g., from endocarditis, skin infections, IV drug use).
- Less common: Candida species (immunocompromised patients).
Risk Factors
- 🍬 Metabolic: Diabetes mellitus (impaired immunity).
- Urological: Recurrent UTIs, urolithiasis (especially staghorn calculi), urinary obstruction, neurogenic bladder, vesicoureteric reflux.
- Structural: Congenital abnormalities, polycystic kidney disease, obstructing tumours, papillary necrosis.
- Other: Pregnancy, IV drug abuse, immunosuppression, chronic dialysis.
🩺 Clinical Features
- Classical triad: Flank pain + fever + flank mass (present in <50% of cases).
- Severe unilateral flank or abdominal pain radiating to groin.
- Persistent high-grade fever despite appropriate antibiotics for pyelonephritis.
- Systemic symptoms: Rigors, malaise, fatigue, weight loss (subacute presentation).
- Urinary symptoms: Dysuria, frequency, haematuria (may be absent if haematogenous origin).
- Examination: Flank tenderness, palpable mass (if large), psoas sign if psoas involvement.
🔎 Investigations
- 🧪 Blood tests: FBC (leucocytosis), elevated CRP/ESR, U&E (assess renal function), blood cultures (positive in 40–60% of cases).
- Urine: Urinalysis and culture → positive in only ~30% of cases (especially if haematogenous source). Pyuria common.
- CT abdomen/pelvis with IV contrast (gold standard): Hypodense fluid collection in perirenal space with rim enhancement. Gas bubbles if gas-forming organisms. Extension into psoas or pelvis. Associated renal stones or obstruction.
- Ultrasound: May demonstrate hypoechoic collection but less sensitive than CT. Useful for drainage guidance.
⚠️ Complications
- Life-threatening: Sepsis, septic shock, multiorgan failure.
- Local spread: Rupture into peritoneal cavity (peritonitis), extension through diaphragm (empyema, subphrenic abscess), psoas abscess.
- Respiratory: Pneumonia, pleural effusion.
- Chronic: Chronic renal impairment, recurrent infections.
💊 Management
- 🚑 Resuscitation: ABC assessment, IV fluid resuscitation, oxygen if required, treat sepsis aggressively.
- Empirical IV antibiotics: Broad-spectrum coverage (e.g., Co-amoxiclav + Gentamicin OR Piperacillin-tazobactam ± Gentamicin). Add anti-staphylococcal cover if IVDU or suspected haematogenous source. Adjust based on culture results. Prolonged course typically 4–6 weeks (including oral step-down).
- 🔪 Source control - drainage indications: Abscess >3–5 cm diameter OR failure to improve after 48–72 hours of appropriate antibiotics OR gas-forming organisms OR multi-loculated collections. Immunocompromised patients may require earlier intervention.
- 🩻 Drainage methods: Percutaneous drainage (ultrasound or CT-guided) is first-line. Open surgical drainage if percutaneous access not feasible, multi-loculated, or failed percutaneous drainage.
- Urology referral: Urgent consultation for drainage planning and to address underlying urological pathology (stones, obstruction).
- Monitor: Serial inflammatory markers, imaging to confirm resolution, repeat drainage if inadequate response.
Prognosis
- Mortality: 10–20% if untreated or delayed diagnosis. <5% with prompt drainage and antibiotics.
- Delay in diagnosis increases morbidity and mortality significantly.
References
