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Overview
Renal artery stenosis (RAS) is the
narrowing of the lining 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 hypertension.
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% 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) and Fibromuscular Dysplasia (FMD)
AS-RAS is due to the build-up of cholesterol on
the inner lining of the renal artery. It is
exceedingly more common then the unusual case of
FMD-RAS.
FMD-RAS
FMD-RAS occurs almost exclusively in women aged 30
to 40 and 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 stenting. After plasty long-term
patency of the lesion is typically seen.
Incidence and Prevalence
Renal vascular disease accounts for less than 1%
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 % of all hypertension. FMD RAS occurs
almost exclusively in women aged 30 to 40 and
rarely affects African Americans or Asians.
Risk Factors
Risk factors associated with the
development of atherosclerotic RAS include the
following:
-
Carotid artery disease
-
Coronary artery disease
-
Diabetes mellitus
-
Hypertension (high blood
pressure)
-
Obesity
-
Old age
-
Peripheral vascular disease
(vascular disease in the extremities, e.g., the
legs)
-
Smoking
There is often a familial history
of FMD RAS.
Causes
Most RAS is caused by
atherosclerosis or "hardening of the arteries."
Atherosclerosis is the build up of cholesterol
deposits, or plaque, in the lining of the
arteries.
Signs and Symptoms
Conditions that may indicate
atherosclerotic RAS include the following:
-
Asymmetrical (differently sized
and shaped) kidneys seen on ultrasound
-
History of calf pain when walking
— indicates impaired circulation to the legs
-
Intolerance of specific
antihypertensive medications — angiotensin-I
(ACE-I) inhibitors or angiotensin receptor
blockers (ARBs) — with a sudden worsening of
renal function
-
More than three antihypertensive
medications needed for blood pressure control
-
New onset of hypertension in a
patient over 55
-
Presence of a bruit (sound or
murmur heard with a stethoscope) in the abdomen
(e.g., groin), neck, or other area
-
Sudden worsening of hypertension
in a patient whose hypertension had been well
controlled, especially if the patient is over 60
Diagnosis
The diagnostic method used for
renal artery stenosis (RAS) is similar to that
used for ischemic nephropathy. The physician may
also measure and compare the level of renin,
(blood pressure–regulating hormone released by the
kidneys), within the right to the left renal
veins. If the amount of renin that is released by
one-side is markedly higher than the other, this
identifies a high renin-releasing kidney
consistent with RAS.
Treatment
Medication is used to control
hypertension (high blood pressure). The class of
blood pressure medications that directly affect
the renin angiotensin pathway can be exceedingly
effective in blood pressure control. The ACE
inhibitors and the new class of angiotensin
receptor blockers can have incredible
effectiveness. Sometimes patients with RAS are
resistant to medication for control of blood
pressure.
Angioplasty
and stenting may be used to improve blood
flow. The goal is to improve the circulation of
blood flow to the kidney and prevent the release
of excess renin, which can help to decrease blood
pressure. This helps to prevent atrophy of the
kidney. In general, patients with AS-RAS should
have stenting done because plasty by itself has a
very high incidence of re-stenosis.
Surgery
to bypass the narrowing may be performed. If the
kidney with RAS has atrophied, a nephrectomy,
surgical removal of the kidney, may be advised.
Prognosis
Patients with fibromuscular dysplasia (FMD) RAS
often have good, long-term results with
angioplasty, but those with atherosclerotic RAS
frequently experience a recurrence. Even after
partial or complete repair of the narrowed blood
vessel, most patients still have hypertension, but
require less medication to control it.
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