Review Question - QID 213495

This patient with endocarditis and sudden-onset back pain, costovertebral angle tenderness, hematuria, and a wedge-shaped contrast defect on CT has an infarction of renal parenchyma.

Renal infarction occurs when interruption of renal blood flow (typically arterial occlusion) causes hypoxia and cell death. Such arterial occlusion can be caused by a local thrombus (e.g. in a patient with atherosclerosis or a hypercoagulable state) or distant thromboembolus. Such thromboemboli are most often cardiac (e.g. valvular vegetations in endocarditis or atrial emboli in atrial fibrillation) and/or iatrogenic (following percutaneous angioplasty or angiography). Renal infarction classically manifests with back/flank pain, costovertebral angle tenderness and hematuria in a patient with known risk factor(s) (e.g. atherosclerosis, atrial fibrillation, endocarditis, hypercoagulable state, and recent angiography). Nausea and vomiting and/or hypertension may also occur. A wedge-shaped infarct in the kidney, visible on CT scan and gross pathology, is pathognomonic.

Figure/Illustration A is an abdominal CT scan with IV and oral contrast, demonstrating a wedge-shaped contrast defect (red arrows) through the cortex and medulla of the right kidney due to a renal infarction.

Incorrect Answers:
Answer 1: Bacterial seeding of lumbar vertebrae (causing osteomyelitis) can cause severe back pain in a patient with bacterial endocarditis but would cause spinal (rather than CVA) tenderness and not cause hematuria. CT scan may show vertebral abnormalities (though MRI is more sensitive).

Answer 2: Immune complex deposition in renal glomeruli occurs in some forms of nephritic and nephrotic syndromes, causing acute kidney injury, but not acute pain or gross abnormalities on imaging.

Answer 3: Infection of the kidney (pyelonephritis) presents with back/flank pain and tenderness, fever, and urinary symptoms (e.g. dysuria). Pyuria (leukocytes) would be seen on urinalysis, and imaging may show hydronephrosis.

Answer 5: Stone formation (nephrolithiasis) also presents with back/flank pain, tenderness, and hematuria. However, imaging would show a stone and/or signs of obstruction (e.g. dilated renal pelvis and/or ureter), rather than a wedge-shaped infarct.

Bullet Summary:
Renal infarction classically presents with sudden back/flank pain and costovertebral angle tenderness in a patient with risk factors (e.g. endocarditis, atrial fibrillation) and a wedge-shaped infarct, seen on imaging and gross pathology.