A 64-year-old man comes to the emergency department due to flank discomfort and red urine. He has a history of hypertension and type 2 diabetes mellitus. Three months ago, the patient had an ischemic stroke and now has mild, residual, right-sided weakness. Serum creatinine is 0.9 mg/dL, and serum lactate dehydrogenase is elevated. Urine microscopy shows many red blood cells. The findings of a CT scan of the abdomen with contrast are shown in the image below: Which of the following is the most likely cause of this patient's symptoms?

Question

A 64-year-old man comes to the emergency department due to flank discomfort and red urine.  He has a history of hypertension and type 2 diabetes mellitus.  Three months ago, the patient had an ischemic stroke and now has mild, residual, right-sided weakness.  Serum creatinine is 0.9 mg/dL, and serum lactate dehydrogenase is elevated.  Urine microscopy shows many red blood cells.  The findings of a CT scan of the abdomen with contrast are shown in the image below:  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_38e7_f66c_9249_ed1c931cefde_MD0001_00 This patient with flank pain, hematuria, and a wedge-shaped kidney lesion on CT scan likely has a renal infarction, which results from interruption of the normal blood supply to the kidney. The lack of collaterals between segmental renal arteries ("end-organ" blood supply) means that any interruption of blood flow can lead to coagulative infarcts. Common laboratory findings include elevated lactate dehydrogenase (reflecting cell necrosis), mild leukocytosis, and hematuria. Serum creatinine is usually normal due to compensation by the unaffected kidney. Macroscopically, renal infarcts appear as pale wedges, with the base (widest part) at the renal cortex and the apex pointing to the medulla. The most common cause of renal infarction is systemic thromboembolism from the left atrium or ventricle. Thromboembolism is a common complication of atrial fibrillation because the irregular contractions lead to sluggish, uneven flow in the left atrium and facilitate clot formation. Emboli from atrial fibrillation, which can be paroxysmal (thereby going undiagnosed), may have also caused this patient's recent stroke. The brain and kidneys are more likely than other organs to suffer embolic infarctions because they are perfused at a higher rate. (Choice B) Lower extremity venous thromboembolism can lead to pulmonary embolism because returning blood passes through the right heart and subsequently to the lungs. Although communication from the right to the left side of the heart (eg, atrial or ventricular septal defect) can allow for systemic (paradoxical) embolus to the brain or kidneys, this is relatively rare. (Choice C) Focal segmental glomerulosclerosis manifests as nephrotic syndrome. Urinary loss of certain natural anticoagulants (eg, antithrombin III) leads to a hypercoagulable state. However, this rarely causes systemic embolization and patients usually have elevated creatinine. (Choice D) Acute interstitial nephritis, a hypersensitivity reaction that can occur 1-2 weeks after starting a new medication, presents with fever, rash, elevated creatinine, eosinophilia, and eosinophiluria. (Choice E) Pulmonary hypertension can cause right-sided heart failure (cor pulmonale) and is sometimes associated with secondary polycythemia, causing increased blood viscosity. Although thrombotic complications may occur, embolic complications are less common. Educational objective: Renal infarction presents with flank pain, hematuria, elevated lactate dehydrogenase, and a wedge-shaped kidney lesion on CT scan. The most common cause of renal infarction is systemic thromboembolism, often due to thrombus formation during atrial fibrillation. The brain and kidneys are more likely than other organs to suffer embolic infarctions because they are perfused at a higher rate.

A 64-Year-Old Man Comes to the Emergency Department Due to Flank