24-12: Renal Artery Stenosis

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

Renal artery stenosis is a relatively common cause of secondary hypertension and can lead to CKD and ESKD. It typically occurs among persons over 45 years of age with atherosclerotic factors such as diabetes mellitus, hyperlipidemia, and tobacco use; disease in other vessels is common. Fibromuscular dysplasia, a less common cause of renal artery stenosis, usually occurs in young women.

CLINICAL FINDINGS

A. Symptoms and Signs

Patients with atherosclerotic renovascular disease may have refractory hypertension, new-onset hypertension (in an older patient), pulmonary edema with poorly controlled blood pressure, and/or AKI upon starting an ACE inhibitor or ARB. Physical examination may reveal an audible abdominal bruit on the affected side. Unexplained hypertension in a woman younger than 40 years should raise suspicion for fibromuscular dysplasia.

B. Laboratory Findings

Serum creatinine may be elevated if there is significant renal ischemia. Patients with bilateral renal artery stenosis may have hypokalemia, a finding that reflects activation of the renin-angiotensin-aldosterone system in response to reduced blood flow (a “prerenal” state). Plasma renin concentration or activity is elevated.

C. Imaging

Abdominal ultrasound can reveal either asymmetric kidney size (greater than 1.5 cm difference) if one renal artery is primarily affected, or small hyperechoic kidneys if both are affected.

Screening with Doppler ultrasonography, CT angiography, or magnetic resonance angiography (MRA) is recommended if a corrective procedure would be performed when a positive test result is found. Doppler ultrasonography can be both sensitive and specific but is extremely operator- and patient habitus–dependent and may be a poor choice for patients with obesity, unable to lie supine, or have interfering bowel.

CT angiography consists of intravenous contrast injection with digital subtraction arteriography and offers good sensitivity and specificity.

MRA is an excellent but expensive way to screen for renal artery stenosis, particularly in those with atherosclerotic disease. The newer-generation gadolinium contrast agents seem to carry little to no risk for nephrogenic systemic fibrosis in those with advanced CKD or ESRD.

Renal angiography is the gold standard for diagnosis, but it is more invasive than the three screening tests discussed above. Thus, it is usually performed after a positive screening test and when concurrent angioplasty and stenting of critically stenotic lesions is clinically appropriate. CO₂ subtraction angiography can be used to minimize risk of contrast nephropathy in high-risk patients. Atherosclerotic lesions are most commonly found in the proximal third or ostial region of the renal artery; there is risk of atheroembolic phenomena after angiography in these patients. ...