Renal Artery Stenosis

The term renal artery stenosis (RAS) applies to a cluster of disease conditions with varying etiologies. The most prominent among them are fibromuscular dysplasia and atherosclerotic RAS (ARAS). Renal artery stenosis is a variant of peripheral arterial disease and ARAS accounts for 90% of all cases.

ARAS usually occurs in older individuals, may present with hypertension or renal insufficiency and has an equal prevalence in men and women. In contrast, fibromuscular dysplasia is more often seen in the young, in women, and is usually associated with hypertension without renal insufficiency.

Other causes include:

• Vasculitic conditions
• Congenital fibrous bands
• Compression of the renal arteries by unavoidable masses
• Radiation-induced injury

ARAS accounts for more than 90% of RAS. Risk factors for ARAS include a history of heart disease or patients who are posted for cardiac catheterization.

Renovascular diseases are divided into two broad subtypes: hypertension and nephropathy.

Signs and symptoms

Renal artery stenosis is always a unilateral condition. The mechanism of RAS is commonly the result of underperfusion of the kidneys because of the proximal stenosis of the renal artery. This leads to activation of the renin-angiotensin-aldosterone axis. This leads to no symptoms in most cases, but in some cases, patients may suffer from hypertension, nephropathy and eventually congestive cardiac failure.

Signs of a failing kidney may include:

• Atrophy of one kidney
• Unexplained rapid-onset pulmonary edema
• Many leg or heart vessels with atherosclerosis

Complications

RAS may lead to any of the following:

• High blood pressure
• Congestive cardiac failure
• Prevention of nephropathy

Diagnosis and treatment

Diagnosis is based on the history backed up by imaging tests, preferably ultrasound scan, with renal angiograms as required. CT angiogram (CTA) is performed. Treatment is mainly supportive, with antihypertensives and a good control of cholesterol and blood sugar. Other desperate measures include anti-smoking and the decision to control cholesterol levels. Antiplatelet drugs may be prescribed. Renal revascularization is a final option.

Even the small accessory renal arteries can be detected by CTA because of its high spatial resolution. It is also preferred for patients who have implanted devices, for patients with limited breath-hold capacity (requiring shorter acquisition times), and for patients with claustrophobia. However, CTA has less specificity than MRA for detecting hemodynamically significant ARAS. It cannot be used safely in patients with borderline renal dysfunction because of the necessity of iodinated contrast agents. Images obtained with CTA are difficult to interpret in heavily calcified arteries and CTA requires use of ionizing radiation.

Magnetic resonance angiography has a reported sensitivity and specificity of 90% to 100% and does not require use of iodinated contrast or radiation. MRA should not be used in patients with certain implanted devices (ie, pacemakers, defibrillators, cochlear implants and spinal cord stimulators) or in claustrophobic patients.

In addition to assessing the severity of ARAS, angiography can detect intrarenal vascular abnormalities and anatomic abnormalities of the kidneys, renal arteries and aorta. Digital subtraction angiography improves contrast resolution and may decrease the volume of contrast needed to as little as 15 mL. arterial trauma, spasm or thromboembolic phenomenon.

Use of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers to inhibit the sympathetic and renin-angiotensin systems, respectively, is recommended for controlling hypertension and for reducing clinical events in those with known cardiovascular disease.

Patients with uncontrolled renovascular hypertension, despite optimal medical therapy, ischemic nephropathy and cardiac destabilization syndromes who have severe RAS, are likely to benefit from renal artery revascularization. When revascularization is deemed appropriate, atherosclerotic RAS is most often treated with stent placement. However, patients with fibromuscular dysplasia are usually treated with balloon angioplasty.

Prognosis

Patients with impaired renal function can develop contrast-induced nephropathy if iodinated contrast is used but generous fluid hydration before contrast administration can effectively prevent this complication. Almost 27% of the patients had progressive renal failure because of the inevitable loss of renal mass.

References

• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127560/
• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4801483/
• http://www.ncbi.nlm.nih.gov/pubmed/24113662