Renal artery stenosis
Updates to Article Attributes
Renal artery stenosis (RAS) refers to a narrowing of a renal artery. When the process occurs slowly, it leads to secondary hypertension. Acute renal artery stenosis does not lead to hypersecretion of renin.
Pathophysiology
When the stenosis occurs slowly, collateral vessels form and supply the kidney. The kidney wrongly senses the reduced flow as low blood pressure (via juxtaglomerular apparatus) and releases large amount of renin, that converts angiotensinogen to angiotensin I. Angiotensin I is then converted to angiotensin II with the help of angiotensin converting enzyme (ACE) in lungs. Angiotensin II is responsible for vaso-constriction and release of aldosterone which causes sodium and water retention, thus resulting in secondary hypertension.
It may be mimicked by several pathological processes :
- atherosclerosis ~ 75% involves proximal renal artery
- fibromuscular dysplasia ~ 20% involves distal renal artery
- vasculitides (especially polyarteritis nodosa, Takayasu arteritis, radiation)
- neurofibromatosis type 1
- abdominal aortic coarctation
- aortic dissection
- segmental arterial mediolysis
Occurrence is not uncommon following a renal transplant.
Radiographic features
Ultrasound
Ultrasound although most freely available, cheap and often used first line, is relatively operator dependent and time consuming.
- increased renal arterial resistive index (RI)
-: some consider a value of 60% to be regarded as significant ref - increased peak systolic velocity (PSV)
-: some advocate 180cm/s 4 - increased renal-interlobar ratio (RIR)
-: some advocate values greater than 5 3 - increased renal aortic ratio (RAR)
-: usually taken as >3.5 although some advocate greater than 3 4 - turbulent flow in post stenotic area
- pulsus parvus tardus
wave formwaveform due to stenosis
CT angiography
The three-dimensional reconstruction of the renal vascular tree provides a reliable method of visualizing the whole vascular tree. Sensitivity and specificity varying formbetween 90 to 99% have been reported 7 .
MR angiography
Two different imaging methods can be used:
- time of flight
, wherein: wherein the high velocity of the blood jet at the level of stenosis appears as a loss of signal (black) - phase contrast technique
, wherein: wherein gadolinium is used as a contrast agent
Three-dimensional reconstruction technique offers a sensibility andsensitivity and specificity values around 90 to 100% 7 .
Nuclear imaging
ACE inhibitor scintigraphy
- affected kidney with renovascular hypertension shows impaired function due to ACE inhibition; based on this principle scintigraphy has been very much useful for diagnosis of renal artery stenosis
- it is performed by IV administration of enalapril maleate after 15 minutes
. - sequential images and scintigraphic curves are drawn for renal cortex and pelvis; renal uptake is measured for every 1-2 min interval after giving IV injection
. - typical isotopes used are Tc99 m MAG3 or I 131OIH
. - scintigram
interpretation is donewill be intereprted as- 1) Low probability 2)either low, intermediateprobability 3)or high probability.
-<li>increased <a href="/articles/renal-arterial-resistive-index">renal arterial resistive index </a>(RI) - some consider a value of 60% to be regarded as significant <sup>ref</sup>- +<li>increased <a href="/articles/renal-arterial-resistive-index">renal arterial resistive index </a>(RI): some consider a value of 60% to be regarded as significant <sup>ref</sup>
-<li>increased <a href="/articles/peak-systolic-velocity-">peak systolic velocity </a>(PSV) - some advocate 180cm/s <sup>4</sup>- +<li>increased <a href="/articles/peak-systolic-velocity-">peak systolic velocity </a>(PSV): some advocate 180cm/s <sup>4</sup>
-<li>increased <a href="/articles/renal-interlobar-ratio">renal-interlobar ratio </a>(RIR) - some advocate values greater than 5 <sup>3</sup>- +<li>increased <a href="/articles/renal-interlobar-ratio">renal-interlobar ratio </a>(RIR): some advocate values greater than 5 <sup>3</sup>
-<li>increased renal aortic ratio (RAR) - usually taken as >3.5 although some advocate greater than 3 <sup>4</sup>- +<li>increased renal aortic ratio (RAR): usually taken as >3.5 although some advocate greater than 3 <sup>4</sup>
-<li>pulsus parvus tardus wave form due to stenosis</li>-</ul><h5>CT angiography</h5><p>The three-dimensional reconstruction of the renal vascular tree provides a reliable method of visualizing the whole vascular tree. Sensitivity and specificity varying form 90 to 99% have been reported <sup>7</sup> .</p><h5>MR angiography</h5><p>Two different imaging methods can be used:</p><ul>-<li>time of flight, wherein the high velocity of the blood jet at the level of stenosis appears as a loss of signal (black)</li>-<li>phase contrast technique, wherein gadolinium is used as a contrast agent</li>-</ul><p>Three-dimensional reconstruction technique offers a sensibility and specificity values around 90 to 100% <sup>7</sup> .</p><h4><sup>Nuclear imaging</sup></h4><h5><sup>ACE inhibitor scintigraphy</sup></h5><ul>- +<li>pulsus parvus tardus waveform due to stenosis</li>
- +</ul><h5>CT angiography</h5><p>The three-dimensional reconstruction of the renal vascular tree provides a reliable method of visualizing the whole vascular tree. Sensitivity and specificity varying between 90 to 99% have been reported <sup>7</sup> .</p><h5>MR angiography</h5><p>Two different imaging methods can be used:</p><ul>
- +<li>time of flight: wherein the high velocity of the blood jet at the level of stenosis appears as a loss of signal (black)</li>
- +<li>phase contrast technique: wherein gadolinium is used as a contrast agent</li>
- +</ul><p>Three-dimensional reconstruction technique offers a sensitivity and specificity values around 90 to 100% <sup>7</sup> .</p><h4><sup>Nuclear imaging</sup></h4><h5><sup>ACE inhibitor scintigraphy</sup></h5><ul>
-<li>it is performed by IV administration of enalapril maleate after 15 minutes .</li>-<li>sequential images and scintigraphic curves are drawn for renal cortex and pelvis; renal uptake is measured for every 1-2 min interval after giving IV injection.</li>-<li>typical isotopes used are Tc99 m MAG3 or I 131OIH .</li>-<li>scintigram interpretation is done as - 1) Low probability 2) intermediate probability 3) high probability .</li>- +<li>it is performed by IV administration of enalapril maleate after 15 minutes</li>
- +<li>sequential images and scintigraphic curves are drawn for renal cortex and pelvis; renal uptake is measured for every 1-2 min interval after giving IV injection</li>
- +<li>typical isotopes used are Tc99 m MAG3 or I 131OIH</li>
- +<li>scintigram will be intereprted as either low, intermediate or high probability</li>
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