Renal Artery Stenosis

Renal Stenosis is characterized by narrowing of the renal artery. Be aware that mild stenosis is normal and causes only minor hemodynamic effect. Significant renal artery stenosis is the most common cause of secondary hypertension. Stenosis reduces renal blood flow, which triggers the juxtaglomerular apparatus (JGA) in the kidney and activates the renin-angiotensin-aldosterone system as follows:

• JGA activation triggers the release of renin, which converts angiotensinogen to angiotensin I
• Angiotensin I is converted to Angiotensin II by Angiotensin-Converting-Enzyme (ACE)
• Angiotensin II increases the retention of sodium and water in the renal tubules (which increases water volume) and activates sympathetic and hormonal vasoconstriction of the peripheral arterial system.

Inappropriate systemic vasoconstriction induces hypertension, ischemic nephropathy, and in severe cases, heart failure and acute coronary syndromes. Renal arterial stenosis can be unilateral or bilateral. The top causes of stenosis are: Atherosclerosis and fibromuscular dysplasia. Atherosclerosis is common in older people, especially those with a history of cigarette smoking. Fibromuscular dysplasia, which is a systemic, noninflammatory, nonatherosclerotic disease of the vascular walls; abnormal cellular proliferation in the arterial walls produces stenosis, which can be unifocal or multifocal with a "string of beads" appearance.

• Fibromuscular dysplasia is more often diagnosed in women, who are 30-50 years old, and, in addition to arterial stenosis, can also cause aneurysms, dissection, and tortuosity.

We suspect renal artery stenosis in patients who have sudden onset of hypertension without a family history.

• In these patients, hypertension is severe and resistant to antihypertensive agents.

We may hear abdominal bruits. Patients with bilateral renal artery stenosis (or unilateral stenosis in single-kidney patients) may present with Pickering syndrome, which is characterized by "flash" pulmonary edema. Renal arteriogram (contraindicated in patients with renal failure, as the contrast dye is nephrotoxic); MRA (magnetic resonance angiography), and Duplex Doppler ultrasonography. If these non-invasive tests are not conclusive, we can use catheter angiograph. We can use antihypertensives drugs, diuretics, statins, and antiplatelet therapies. Be aware that we need to monitor patients for acute kidney injury. ACE inhibitors are contraindicated in patients with bilateral renal artery stenosis or unilateral stenosis in single-kidney patients. Percutaneous renal artery stenting may be necessary in severe cases of atherosclerotic renal artery stenosis, and it is often curative in fibromuscular dysplasia.