Most sensitive and specific investigation for screening of Renovascular hypeension
C i.e. Spiral CT Scan (CTA) - The presence of aerial collaterals indicates that renal aery stenosis is hemodynamically significantQ. The diameter of stenotic segment may also give an indication of hemodynamic significance, but is only reliable if the stenosis is either very severe or minimal. Conventional contrast renal aeriography (or digital substraction angiography or intraaerial catheter angiography) is the gold standard for diagnosis of renal aery stenosisQ against which all other modalities are compared. On angiography, the presence of collateral vessels to the ischemic kidneyQ suggest a functionally significant lesion (i.e. a lesion that occludes >70% of lumen of affected renal aery). A lateralizing renal vein renin ratio (>1.5 of affected side/contralateral side) has a 90% predictive value for a lesion that would respond to vascular repair and result in BP control. After percutaneous aeriography, the next most sensitive and specific screening test for diagnosis of RAS is CT angiographyQ (using spiral and more recently multidetector CT) almost equvalent to DSA. However, it requires use of large amount of iodinated contrast medium (like IVP) precluding its use in renal insufficiency and also exposes to ionizing radiation. - Captopril enahanced radionuclide renal scintigraphy, is most widely performed screening test for diagnosis of renovascular hypeension, (neither most sensitive nor most specific). 99mTcMAG 3 is slightly preferred over 99mTc-DTPA; 131IOIH is not used now. It can be used as screening test to establish hemodynamic significance of RAS, to predict the outcome of revascularizaation and in the follow up after successful revascularization. Disadvantages include low sensitivity in patients with azotemia or underlying renal dysfunction & with bilateral RAS. Branch aery stenosis cannot be diagnosed and provides functional not anatomical data. Summary: The decreasing order of sensitivity & specificity for diagnosis of renal aery stenosis (related renovascular hypeension) is conventional contrast / intraaerial-catheter angiography >CT angiography (using spiral/MDCT) > CE-MRA (dynamic) > SSFP non contrast. enhanced MRA > captopril enhanced radionuclide renal scintigraphy (99mTcMAG3 and 99mTcLLEC preferred over 99mTcDTPA). All have their pros & cons.
MRI
Captopril enhanced radionuclide scan
Spiral CT angiography (CTA)
Duplex - Doppler flow study