What are the causes of renal infarcts?

Causes of Renal Infarction

Renal infarction is primarily caused by cardioembolic events, renal artery injury, hypercoagulable states, and idiopathic factors, with cardiogenic sources accounting for approximately 55-60% of all cases.

Major Etiologies

1. Cardioembolic Sources (55-60% of cases)

• Atrial fibrillation: Most common cardiac cause 1
• Myocardial infarction: Can lead to mural thrombi formation 2
• Valvular heart disease: Particularly with vegetation formation
• Cardiomyopathy: Leading to stasis and thrombus formation

2. Renal Artery Injury (7-8% of cases)

• Atherosclerotic disease: Particularly at the aorto-ostial junction 3
• Arterial dissection: Can occur spontaneously or following trauma
• Fibromuscular dysplasia (FMD): More common in younger patients 3
• Trauma: High-velocity deceleration injuries causing vascular damage 4
• Iatrogenic causes: Following endovascular procedures or surgery

3. Hypercoagulable States (6-7% of cases)

• Inherited thrombophilias: Protein C/S deficiency, Factor V Leiden 5
• Antiphospholipid syndrome
• Malignancy-associated hypercoagulability
• Pregnancy and postpartum states

4. Vasoconstrictive Medications/Substances

• Vasoconstrictive drugs: Sumatriptan and other triptans 6
• Combination of vasoconstrictive agents: Particularly when used with calcineurin inhibitors 6

5. Systemic Vasculitis

• Polyarteritis nodosa
• ANCA-associated vasculitis
• Fabry disease: Progressive accumulation of globotriaosylceramide in vascular endothelium leading to ischemia and infarction 3

6. Idiopathic (25-30% of cases)

• No identifiable cause despite thorough investigation 1

Risk Factors

• Advanced age: Mean age of presentation is 60-70 years 5, 7
• History of atrial fibrillation: Present in majority of cardioembolic cases 5
• Previous thromboembolic events: Increases risk of recurrence 5
• Inadequate anticoagulation: Subtherapeutic INR in patients requiring anticoagulation 5
• Atherosclerotic vascular disease: Particularly affecting renal arteries 3
• Renal transplantation: Especially with concomitant use of calcineurin inhibitors 6

Clinical Presentation

• Flank pain: Present in >90% of cases 5
• Fever: Common in about 40-50% of cases 5
• Nausea/vomiting: Present in approximately 30-40% of cases 5
• Hematuria: Almost universally present on urinalysis 5
• Laboratory abnormalities: Elevated LDH and leukocytosis are consistent findings 5

Diagnostic Challenges

• Frequently misdiagnosed initially as renal colic, pyelonephritis, or acute abdomen 5
• Diagnosis often delayed by 24 hours to several days 5
• High clinical suspicion required in patients with risk factors presenting with flank pain

Outcomes and Prognosis

• Acute kidney injury: Occurs in approximately 20% of patients 1
• New-onset reduced eGFR: Develops in about 11% of patients 1
• End-stage renal disease: Progression occurs in 2-3% of cases 1
• Mortality: 5% during initial hospitalization 1
• Recurrence: Approximately 3% risk of recurrent infarction 1

Key Prognostic Factors

• Initial renal function: Strong predictor of outcomes 7
• Previous anticoagulation treatment: Associated with better outcomes 7
• Extent of infarction: Larger infarcts correlate with worse outcomes
• Bilateral involvement: Associated with higher risk of renal failure
• Underlying etiology: Cardioembolic causes may have better prognosis than vasculitis

Early recognition and appropriate management of renal infarction are crucial to minimize permanent renal damage and prevent recurrence. Contrast-enhanced CT is the diagnostic modality of choice, and treatment typically involves anticoagulation unless contraindicated.