Renal Infarction

Renal infarction is ischaemic necrosis of renal parenchyma caused by occlusion of the renal artery or its branches.

• Embolic (most): atrial fibrillation, left ventricular thrombus after myocardial infarction, infective endocarditis, valvular disease, atrial myxoma, paradoxical emboli, aortic atheroma.
• Thrombotic: renal artery dissection (spontaneous or traumatic), fibromuscular dysplasia, atherosclerosis, vasculitis (polyarteritis nodosa, Takayasu), hypercoagulable states, antiphospholipid syndrome, sickle cell disease, renal artery aneurysm, and iatrogenic injury after angiography or stent.
• It is frequently underdiagnosed (mimics renal colic and pyelonephritis).

Acute flank or abdominal pain, nausea, vomiting, fever, haematuria, new or worsening hypertension.

• Possible oliguria or anuria with bilateral or solitary kidney infarction.
• Raised lactate dehydrogenase (peaks at 24 to 48 hours), leucocytosis, raised creatinine in bilateral disease.
• Differential diagnosis: renal colic, pyelonephritis, appendicitis, diverticulitis, cholecystitis, pancreatitis, mesenteric ischaemia, aortic dissection, myocardial infarction, pulmonary embolism, musculoskeletal pain.
• Complications: acute kidney injury, chronic kidney disease, renovascular hypertension, abscess formation, further emboli (mesenteric, splenic, cerebral), end stage kidney disease and death.

Creatinine, urea, electrolytes, urinalysis (haematuria, mild proteinuria), lactate dehydrogenase (above 2 times normal common), full blood count, C-reactive protein.

• Contrast-enhanced CT or CT angiography is the best test: wedge-shaped perfusion defects, absent cortical enhancement, cortical rim sign; main renal artery occlusion or dissection.
• Doppler ultrasound (reduced perfusion) if contrast is contraindicated; magnetic resonance angiography; digital subtraction angiography for intervention.
• Source search: ECG and rhythm monitoring for atrial fibrillation, echocardiography (transthoracic then transoesophageal), blood cultures if fever, thrombophilia and antiphospholipid antibody screen, vasculitis serology, CT or MR angiography of the aorta.

Supportive: analgesia (paracetamol 1 g, morphine 2.5 to 5 mg IV), antiemetics, fluids, blood pressure control, avoid nephrotoxins.

Pharmacological

• Anticoagulation unless contraindicated: unfractionated heparin 80 units/kg IV bolus then 18 units/kg/h to an aPTT of 1.5 to 2.5 times control, or enoxaparin 1 mg/kg twice daily (adjust for renal function), then oral anticoagulation for at least 3 to 6 months; indefinite for atrial fibrillation (rivaroxaban 20 mg daily with food, or apixaban 5 mg twice daily, or warfarin to an INR of 2 to 3) and for hypercoagulable states.
• Infective endocarditis: appropriate antibiotics (for example flucloxacillin 2 g IV every 4 to 6 hours plus gentamicin 3 mg/kg daily in staphylococcal disease) and no anticoagulation unless required; heparin carries bleeding risk.
• Hypertension: ACE inhibitor or angiotensin receptor blocker if function is preserved (caution in bilateral disease); amlodipine 5 to 10 mg daily.
• Thrombolysis: catheter-directed alteplase (up to 0.5 to 1 mg/h infusion) within 3 hours of onset in selected cases with salvageable kidney (bilateral, solitary kidney), balancing bleeding risk.

Procedures: endovascular thrombectomy, aspiration or stenting for main artery occlusion, dissection or stenosis; surgical revascularisation or nephrectomy rarely (abscess, malignant hypertension).

Special groups: solitary kidney or bilateral infarction (urgent revascularisation), young patients (look for dissection, antiphospholipid syndrome, vasculitis), pregnancy (low molecular weight heparin).

Red flags: anuria, rising creatinine, bilateral disease, refractory hypertension, signs of other emboli.

Follow-up: renal function and blood pressure at 1, 3 and 6 months; imaging at 3 months (renal size); lifelong anticoagulation for atrial fibrillation; assess for hypertension and chronic kidney disease.