Renal Arteries









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    Contrast-enhanced renal MRA is an accurate, noninvasive technique for detecting renal artery stenosis.


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    Phase contrast MRA techniques can be used to assess the hemodynamic significance of a stenosis.


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    MRA plays an important role in the evaluation of vascular complications following renal transplant.


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    Non-contrast-enhanced MRA techniques can be used to noninvasively evaluate the renal vasculature in patients who cannot receive MR contrast agents.



KEY POINTS




Case 1


A 65-year-old woman was referred for renal magnetic resonance angiography (MRA) because of suspected renovascular hypertension ( Figures 22-1 A–C ). In another case, a 52-year-old with acute left flank pain and elevated serum creatinine was referred for contrast enhanced renal MRA ( Figures 22-1 D-E ). Further, we review the case of an 18-month-old boy presenting with fever and hypertension who was referred for contrast enhanced renal MRA. Work-up confirmed a diagnosis of Takayasu arteritis ( Figures 22-1F ). The last case in this section is that of a 76-year-old woman who was referred for CE-MRA with a history of recurrent hypertension following endovascular treatment of left renal artery stenosis with stent ( Figures 22-1 G-H ).






Figure 22-1


A, Multiplanar reformatted (MPR) image created from the contrast-enhanced (CE) MRA data set reveals a severe (greater than 70%) stenosis in the proximal right renal artery ( arrow ). B, MPR image created from the three-dimensional (3D) phase contrast (PC) MRA data set. The image demonstrates signal dropout at the stenosis ( long arrow ) because of aliasing from turbulent, high-velocity flow indicating a hemodynamically significant stenosis. Signal distal to the stenosis is also decreased ( short arrows ) because of decreased flow. C, Images from digital subtraction angiography in the same patient confirms a severe (greater than 70%) stenosis in the proximal right renal artery ( arrow ). Pressure measurements confirmed a hemodynamically significant stenosis, which was subsequently stented. D, Maximum intensity projection (MIP) image from CE-MRA reveals near occlusive stenosis in the proximal left renal artery ( arrow ). E, Image from a coronal postcontrast T1-weighted spoiled gradient echo sequence with fat saturation shows a central filling defect ( arrows ) in the left renal artery, extending into the first segmental arteries, consistent with a left renal artery embolus. F, MIP image from CE-MRA shows smoothly tapered severe stenosis in the proximal left renal artery and moderate stenosis in the proximal right renal artery ( arrows ). G, MIP image from CE-MRA shows an apparent severe stenosis in the proximal left renal artery ( arrows ). The left renal artery distal to this apparent stenosis is well opacified and normal in caliber. H, Coronal source image from CE-MRA shows left renal artery stent causing susceptibility artifact ( circle ). The high signal intensity at the margin of the stent is indicative of susceptibility artifact. Renal artery stents have a variable appearance on CMR, depending on their content. For example, nitinol stents have less susceptibility artifact than steel stents.


Renal Artery Stenosis


Comments


MRA is an accurate and safe technique for evaluating the main renal artery for renal artery stenosis. High sensitivities (85% to 100%) and specificities (86% to 100%) have been reported for the detection of hemodynamically significant renal artery stenosis compared with digital subtraction angiography (DSA). Because of the relatively small size of the renal arteries, grading of renal artery stenosis with MRA is typically done using qualitative (normal, mild, moderate, severe, occlusion) descriptors rather than quantitative measures. In addition, the accuracy of CE-MRA is greater for stenoses located in the proximal renal artery, where its diameter is largest, than stenoses located in the mid or distal renal artery branches. Because of the effects of respiratory motion, CE-MRA techniques are generally preferred over time-of-flight and PC techniques. Although CE-MRA accurately depicts the morphology of the renal vasculature, it does not provide physiologic or hemodynamic information. Hemodynamic information can be obtained with the use of PC-MRA techniques or by using dynamic, time-resolved CE-MRA techniques. In patients with renal artery stents, the images must be reviewed with caution because susceptibility artifact from the metal can mislead one into diagnosing a severe stenosis.




Case 2


A 32-year-old woman was referred for renal magnetic resonance angiography (MRA) because of suspected renovascular hypertension ( Figure 22-2 ).


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Feb 1, 2019 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Renal Arteries

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