Renal artery stenosis

In hospitalized patients acute kidney injury is largely attributed to pre-renal disease, with additional renal and post renal causes being much less likely. Although a trial of fluids is usually tried in the majority of patients its important to recognize when this therapy is failing and other causes of renal should be considered. Renal artery stenosis (RAS) is an uncommon cause of chronic hypertension (less than 1%), but is more likely to be causative in acute refractory cases. In general, RAS can be broken into two classes:

1. Atherosclerotic stenosis (90%)
2. Fibromuscular dysplasia (10%)

Atherosclerotic disease is much more common than FMD given the presence of CAD, DMII, HTN, dyslipidemia and smoking prevalence. It is a progressive disease which usually results in small kidneys and CKD. Fibromuscular dysplasia is an abnormality of the intimal, medial and adventitial layers of the blood vessels of unclear cause. It results in narrowing of the renal arteries, typically at the distal third. Risk factors include being female and HTN prior to age 50. These patients can develop other complications, including artery dissection or thrombosis (most common with intimal involvement).

The pathophysiology is related to poor renal perfusion leading to activation of the renin-angiotensin system, impacting sodium homeostasis, vasodilatory factors and results in renal hypertension. Clinical clues to suspect renal vascular disease in patients with CKD and HTN include:

1. Worsening kidney function of 30% in started and ACEi
2. Systolic/Diastolic renal bruit
3. Onset HTN after 55
4. Flash pulmonary edema
5. Asymmetry in renal size >1.5 cm

Testing for these disease used to involve a captopril renal scan where differences in renal perfusion were examined following administration of an ACEi. However, this is no longer done and has largely been replaced by imaging. Ultrasound with arterial dopplers are helpful, and certain flow velocities through the artery can predict the degree of stenosis. This does however require an experienced radiologists and can be difficult to get appropriate view. CT angiography and MRI are useful tests, but are less likely to image distal vessels appropriately.

All patients are recommended to undergo medical therapy, which involves modification of CAD risk factors, including smoking cessation. ACEi will preferentially vasodilate the efferent renal artery, counteracting the natural response to improving GFR in patients with afferent renovascular disease. The addition of an ACEi can decrease GFR and worsen AKI. That being said, they can still be used in this disease and one must consider the clinical context. This is more problematic inpatients with atherosclerotic disease as opposed to FMD.

Renal artery angioplasty has not been shown to be superior to medical therapy in a meta-analysis published in the American Heart Journal in 2011. However, patients with refractory hypertension and flash pulmonary edema, may be considered for angioplasty. See this NEJM review on RAS for additional details.

Renal artery stenosis review