Renal Artery Stenosis 2

Posted by e-Medical PPT Friday, January 13, 2012
Renal artery stenosis (RAS) is the major cause of renovascular hypertension and it accounts for about 1-10% of the 50 million people in the United States who have hypertension. The incidence is less than 1% of cases of mild to moderate HTN. However, it rises to 10 to 45 % in patients with acute (or superimposed upon a preexisting elevation in blood pressure), severe, or refractory hypertension.
Renovascular hypertension (RVHT) denotes nonessential hypertension in which a causal relationship exists between anatomically evident arterial occlusive disease and elevated blood pressure. RVHT is the clinical consequence of renin-angiotensin-aldosterone activation as a result of renal ischemia.
RAS is also being increasingly recognized as an important cause of chronic renal insufficiency and end-stage renal disease. Studies suggest that ischemic nephropathy from RAS may be responsible for 5-22% of advanced renal disease in all patients older than 50 years in US.

Major causes of the renal arterial lesions are:
Atherosclerosis —It is the cause of RAS in >2/3rd of the cases. This primarily affects men over the age of 45 and usually involves the aortic orifice or the proximal main renal artery. This disorder is particularly common in patients with diffuse atherosclerosis, but can occur as a relatively isolated renal lesion.
Fibromuscular dysplasia — In comparison to atherosclerosis, fibromuscular dysplasia most often affects younger women and typically involves the distal main renal artery or the intrarenal branches.
Other less common causes of RAS include:
               Vasculitis (Takayasu’s arteritis)
                Dissection of the renal artery. 
                Thromboembolic disease
                Renal artery aneurysm
                Renal artery coarctation
                Extrinsic compression
                Radiation injury

Atherosclerotic Renal Artery Stenosis
The initiator of endothelial injury is not clear; however, dyslipidemia, hypertension, cigarette smoking, diabetes mellitus, viral infection, immune injury, and increased homocysteine levels may contribute to endothelial injury.
In the atherosclerotic lesion site, endothelium permeability to plasma macromolecules (e.g. LDL) increases, turnover of endothelial cells and smooth muscle cells and intimal macrophages also increases. When atherogenic lipoproteins exceed certain critical levels, the mechanical forces may enhance lipoprotein insudation in these regions, leading to early atheromatous lesions. The sites where the initial atherosclerotic lesions developed are more prone to physiological adaptation to mechanical stress secondary to variations in flow and wall tension (e.g. renal artery site).

Fibromuscular dysplasia:
Fibromuscular dysplasias are uncommon angiopathies associated with heterogeneous histologic changes that may affect the carotid circulation as well as the visceral and peripheral arteries.
String of beads is the classic radiographic finding seen in FMD.
FMD, as a cause of RAS usually affects young to middle-aged adults, mostly women, but it can also affect children...

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