Overview of RAS & RVH
Renal artery stenosis (RAS) is the narrowing of the main artery that supplies the kidney. Depending on the degree of narrowing, patients can develop hypertension called renal vascular hypertension (RVH). This form of hypertension is the most common cause of secondary high blood pressure.
RVH occurs when RAS produces a critical narrowing of the artery that supplies one of the kidneys. Critical RAS is defined as at least 70 percent narrowing of the renal artery, based on angiographic (blood vessel x-ray) evaluation.
Reduced blood flow through the renal artery causes the kidney to release increased amounts of the hormone renin. Renin, a powerful blood pressure regulator, initiates a series of chemical events that result in hypertension. Renal vascular hypertension can be very severe and difficult to control.
The kidney with RAS suffers from the decreased blood flow and often shrinks in size (atrophies). This process is called ischemic nephropathy.
The other kidney is at risk for developing damage from the hypertension, often developing hypertensive nephrosclerosis. The persistent elevated blood pressures in this non-stenotic kidney can cause progressive scarring (sclerosis) leading to progressive loss of filtering function in this kidney as well. Both unilateral RAS and bilateral RAS can ultimately lead to chronic renal failure.
Atherosclerotic Renal Artery Stenosis (AS-RAS) & Fibromuscular Dysplasia (FMD)
AS-RAS is due to the build-up of cholesterol on the inner lining of the renal artery. AS-RAS is more common than the unusual case of FMD-RAS. FMD-RAS occurs almost exclusively in women aged 30 to 40 and the condition rarely affects African Americans or Asians. FMD-RAS is due to an abnormality in the muscular lining of the renal artery.
FMD-RAS is often not as well detected on MRA as it is on other non-invasive studies such as, renal scan with ACE-inhibitor challenge, or ultrasound with Doppler interrogation. FMD responds well to angioplasty and following the procedure, long-term patency of the lesion is typically seen.
Incidence and Prevalence of RAS & RVH
Renal vascular disease accounts for less than 1 percent of all hypertension in people who have moderately increased blood pressure. But in certain high-risk groups, renal vascular disease may be the cause of 10 to 40 percent of all high blood pressure. FMD RAS occurs almost exclusively in women aged 30 to 40 and rarely affects African Americans or Asians.