Renal artery stenosis diagnostic criteria
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Shivam Singla, M.D.[2]
Overview
There are numerous tests and procedures involved in the detection of renal artery stenosis. Renal artery stenosis is best diagnosed with MRA(Magnetic resonance Imaging), Doppler ultrasound, Computed tomography, renal scintigraphy, peripheral renin levels, and renal vein sampling. Though these all modalities are used for making the diagnosis but still renal vein sampling, renal scintigraphy are not the first choice for making the diagnosis of renal artery stenosis because of their low sensitivity and specificity which is around 38-40.
Diagnosis
There are numerous tests and procedures involved in the detection of renal artery stenosis. Renal artery stenosis is best diagnosed with MRA(Magnetic resonance Imaging), Doppler ultrasound, Computed tomography, renal scintigraphy, peripheral renin levels, and renal vein sampling. Though these all modalities are used for making the diagnosis but still renal vein sampling, renal scintigraphy are not the first choice for making the diagnosis of renal artery stenosis because of their low sensitivity and specificity which is around 38-40.
The imaging modalities may be considered diagnostic if the following objectives are met:
(1) Anatomic and or Hemodynamic abnormality
(2) Anatomic consequences and complications associated with renal artery stenosis (Post stenotic dilatation of renal artery can be seen with the use of CTA and MRA, shrinkage of renal parenchyma, with kidneys being < 8 cm.
(3) Functional and cellular consequences of renal artery stenosis
(4) Renal impairment criteria related to renovascular disease should be me.
Ultrasonography
Ultrasonography is readily available, secure, and inexpensive, and consequently is usually the first imaging study used to detect Renal artery stenosis. Usually, the results and accuracy are operator dependent and range in between 60-90%. This modality helps in the assessment of
- Renal functional reserve
- Renal resistive index.
A renal artery EDV >90cm/s and RRI< 75-80 represents no microvascular disease. The hemodynamic significant abnormality is concluded with the presence of spectral broadening and increased velocity on USG.
Reno aortic velocity ratio > 3.5 corresponds with 60% stenosis and RAPSV (Renal artery peak systolic velocity) greater than 150cm/s corresponds to 50% stenosis whereas velocity greater than 180cm/s corresponds to 60% stenosis. According to recent studies, the sensitivity and specificity of ultrasound-guided detection of renal artery stenosis are usually 85% and 92% respectively. Severe stenosis is diagnosed on USG with slowed systolic accelerations along with the decreased resistive index.
Quantitative criteria for diagnosing distal stenosis includes early peak systolic acceleration <3m/s2, an acceleration index > 4m/s2, and or greater than 5% difference in RRI between both the kidneys. Because these waveforms are difficult to interpret these criteria are difficult to interpret.
Computed Tomographic Angiography.
CT angiography provides a three-dimensional assessment of the tissue as one of the important tools in the diagnosis of Renal artery stenosis.
- Contraindicated in patients with contrast allergy as this procedure modality involves the ionizing radiations and iodinated contrast medium.
- In patients having underlying renal impairment the use of iodinated contrast can lead to the development of contrast-induced nephropathy, but it can be prevented with the use of hydration before doing the procedure.
- The sensitivity of this procedure is extremely high with 94% and specificity varies between 60% to 90 %.
- CTA can give the detailed resolution of even small accessory renal arteries.
- It is also the diagnostic modality of choice in patients having limited capacity to hold breath and also in patients having claustrophobia.
- At the same time, CTA is having limited diagnostic modality as compared to MRA in detecting clinically significant Renal artery stenosis and also in patients having renal dysfunction
Magnetic Resonance Angiography
MRA is having sensitivity and specificity of 90-100%
- This procedure does not involve the use of iodinated contrast or radiations, unlike CTA.
- In patients with intermediate to end-stage renal failure due to the risk of nephrogenic systemic fibrosis, gadolinium-based contrast media should be avoided.
- Additionally, In patients with the kind of implanted devices (i.e., pacemakers, defibrillators, cochlear implants, and spinal cord stimulators), or in claustrophobic patients, MRA should not be used.
- Contrast reaction associated with MRA is lower as compared to CTA
Angiography
Invasive renal arteriography is an important helpful modality used these days in evaluating Renal artery stenosis.
- Angiography can detect intrarenal vascular abnormalities and anatomical abnormalities of the kidneys, renal arteries, and aorta, in addition to evaluating the severity of RAS.
- Digital angiography by subtraction increases contrast resolution and can minimize the amount of contrast required to as little as 15mL.
- There are risks involved with arterial puncture and catheter/wire stimulation because renal angiography is invasive, which may lead to arterial damage, spasm, or thromboembolic phenomena.
- Carbon dioxide should be used as a non nephrotoxic contrast agent in patients with renal failure or contrast allergy.
- To assess hemodynamic importance before conducting therapeutic procedures such as percutaneous transluminal renal angioplasty (PTRA) or stenting, translesional pressure gradients may be measured across regions of stenosis.