Renal Infarction

Even More Pain
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Diagnosis and reasoning

This elderly gentleman has presented with an acute abdomen, one of the most concerning presentations in this age group. Statistics show that almost 50% of such individuals eventually require hospital admission, and between 20% to 33%, immediate surgery. When faced with an acute abdomen, the first and most important diagnostic clue is the location of the pain; in this patient, the localization to the left upper quadrant suggests at either a cardiac, gastric, pancreatic, renal, or vascular etiology. The abrupt onset of the pain is another potent clue; an acute coronary syndrome could present in this manner, as could vascular catastrophes such as mesenteric ischemia, abdominal aortic dissection, or renal infarction. Other key possibilities include perforation of a peptic ulcer, and ureteric colic. Examination reveals tenderness in the left upper quadrant; this is too nonspecific a sign to be of much help. However, he also has an irregularly irregular pulse, suggesting at atrial fibrillation; this is confirmed by an ECG. While the above may be completely unrelated to the current presentation, it should be kept in mind that atrial fibrillation can give rise to thromboembolic phenomena; thus, both acute mesenteric ischemia and renal infarction should be doubly considered. His basic investigations are all within normal parameters, as is an ultrasound scan of the abdomen; further imaging via a contrast CT scan is a rational next step, as this will help detect most of the above listed etiologies. The CT scan in turn reveals a hypoenhancing wedge-shaped shadow in the upper pole of the left kidney, with a zone of peripheral diminished density without enhancement. This finding is characteristic of a renal infarction, clinching the diagnosis. Anticoagulation is a key element of his management, and should be started as soon as possible; this will help prevent further propogation of the thrombus. That said, this alone will not relieve the renal ischemia; thus, thrombectomy should be considered for definitive management. Note that angioplasty is not indicated here, given that the renal vasculature has no intrinsic abnormalities (e.g. atherosclerosis or fibromuscular dysplasia); neither are intravenous antibiotics of value in his immediate management.


Discussion

Acute renal infarction is rare, with a documented incidence of between 0.004% to 0.007% of hospital admissions; however, the true incidence is almost certainly higher, as the condition is easy to miss and misdiagnose. Most cases are encountered between the sixth or seventh decades of life, with men and women equally affected. In 2% to 20% of instances, bilateral infarcts are found. The primary pathology of renal infarction is occlusion of the renal artery and/or its branches, resulting in infarction and ischemic death of the affected parenchyma. This may occur via several mechanisms: thromboembolism, in-situ thrombosis, renal artery stenosis, and drugs. Atrial fibrillation is the most common cause of thromboembolism; other important etiolgoies include valvular heart disease, and infective endocarditis. In-situ thrombosis may occur in the case of an atherosclerotic renal artery, or in the presence of a hypercoagulable state. Renal arterial stenosis may result from fibromuscular dysplasia, renal dissection, or vasospasm. Drugs implicated in the development of renal infarction include cocaine, tacrolimus, and ergot derivatives (triptans). Flank pain is the most common presenting symptom, being encountered in 86% to 100% of cases; patients may also experience nausea (63%), vomiting (33%), and fever (41%). Common physical findings include abdominal tenderness (74%), and lumbar or flank tenderness (63%). Gross hematuria has also been noted. As previously mentioned, the diagnosis of renal infarction is easy to miss, especially given the non-specific signs and symptoms. Most cases are misdiagnosed as renal stones. In particular, where unilateral flank pain occurs in a patient at increased risk for thromboembolism, and this is associated with hematuria, leukocytosis, and elevation of LDH levels, the condition should be strongly considered. A Doppler scan of the renal arterial and venous systems helps detect global or segmental renal infarction, which will be seen as a filling defect. Note that the former is more likely to be missed. CT imaging with intravenous contrast media has started to become the diagnostic technique of choice. The classic finding is a wedge-shaped zone of peripheral diminished density without enhancement; a hypoattenuated area with an associated mass effect is present in ~32% of cases. The "rim sign" is represented by a rim of viable tissue surrounding non-functional renal parenchyma, and is seen in about 19% of cases. Since an unenhanced helical CT is the investigation of choice for diagnosis of renal colic, it has been suggested that an enhanced CT should be ordered if no calculi are found on the unenhanced scan, so as to increase the likelihood of diagnosing renal infarctions. While renal angiography is the most sensitive and specific imaging test for this condition, it is far more invasive that the previously outlined investigations. Laboratory findings in an acute renal infarction do not contribute to a definitive diagnosis, but may provide supportive evidence. Urinalysis may reveal microscopic hematuria and proteinuria, while blood chemistries may show elevated lactate dehydrogenase (LDH), C-reactive protein (CRP), serum creatinine, and creatinine kinase. Leukocytosis may also be present. Aside from diagnosing acute renal infarction, investigating the causative etiology is important to guide the management. In particular, an electrocardiogram (ECG) and echocardiography will help diagnose atrial fibrillation or infective endocarditis, conditions that give rise to intracardiac thrombi. A thrombophilia panel may also be requested to determine the patient's coagulation state. Considering the management of these patients, anticoagulation was previously the mainstay of treatment, but it is now known to be insufficient in relieving the acute ischemia. Systemic thrombolysis has been employed with success; unfortunately, it carries a significant risk of a major bleeding event and so requires careful monitoring. Advances in endovascular techniques have allowed for the local administration of these agents, thereby minimizing the risk of bleeding. Thrombectomy is an invasive procedure which aims to mechanically fragment and/or aspirate thromboembolic material from occluded arteries; this is now increasingly employed in lieu of thrombolysis. That said, the time frame within which this technique needs to be employed is controversial; further research is necessary but is difficult to accomplish due to the low incidence of renal infarction. The prognosis of an isolated acute renal infarction is good, mainly because the kidney is a bilateral organ. However, significant morbidity and mortality may result if the underlying pathology is not treated and a second thrombotic event is precipitated. Renal functions, if impaired, usually return to baseline in a month; rarely, mild elevations in serum creatinine may persist, but are usually not high enough for the clinical diagnosis of kidney disease. End-stage kidney disease is rare, and if it does occur will often be a complication of a pre-existing comorbidity. Some individuals may develop persistent renin-mediated hypertension.


Take home messages

  1. Acute renal infarction is a rare condition with a non-specific clinical presentation; thus, the diagnosis is often missed or delayed.
  2. The presentation is extremely similar to renal colic, and a high index of suspicion is crucial to correctly arrive at a diagnosis, especially if renal stones have already been ruled out.
  3. Atrial fibrillation is the most common cause of renal thromboembolism, followed by renal atherosclerosis and systemic hypercoagulability.
  4. Contrast enhanced CT is becoming the preferred imaging technique for the diagnosis of renal infarction.
  5. While anticoagulation was the mainstay of treatment earlier, it often does not relieve the acute ischemia; thus thrombolysis and thrombectomy are being increasingly employed.

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