(Radiographics. 1999;19:1555-1568.)
© RSNA, 1999
MR Angiography after Renal Revascularization: Spectrum of Expected Anatomic Results and Postintervention Complications1
Ruth C. Carlos, MD,
Qian Dong, MD,
James C. Stanley, MD and
Martin R. Prince, MD, PhD
1 From the Departments of Radiology (R.C.C., Q.D., M.R.P.) and Surgery (J.C.S.), University of Michigan, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0030. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received March 12, 1999; revision requested April 13 and received June 15; accepted June 21. Supported in part by the Robert Wood Johnson Clinical Scholars Program and the Whitaker Foundation. Address reprint requests to R.C.C.
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Abstract
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The use of magnetic resonance (MR) angiography in screening for renal artery stenosis has been extensively evaluated. However, the MR angiographic findings after renal artery revascularization are not as well characterized. The renal artery and parenchyma can be evaluated after revascularization with a comprehensive MR imaging protocol that includes T1- and T2-weighted spin-echo sequences, three-dimensional (3D) gadolinium-enhanced MR angiography, and 3D phase-contrast MR angiography. Because surgical techniques for revascularization vary, knowledge of the surgical procedure is necessary to ensure inclusion of the pertinent anatomy at 3D gadolinium-enhanced MR angiography and to define appropriate 3D phase-contrast MR angiography volumes. The 3D gadolinium-enhanced MR angiography volume can be manipulated to view relevant vascular anatomy at the optimal obliquity and section thickness. This protocol allows robust, noninvasive evaluation of the expected arterial anatomy after revascularization, including renal artery endarterectomy, aortorenal bypass grafts, and extraanatomic reconstructions. In cases of suspected postrevascularization complications, gadolinium-enhanced MR angiography is useful because of its lack of nephrotoxicity and radiation exposure. Immediate complications of renal revascularization include renal artery thrombosis, renal infarction, and perinephric hemorrhage. Long-term complications include aneurysms of bypass grafts and recurrent stenosis of the renal artery.
Index Terms: Arteries, surgery, 961.45 • Gadolinium • Magnetic resonance (MR), vascular studies, 961.129415, 961.12942 • Renal arteries, MR, 961.129415, 961.12942 • Renal arteries, stenosis or obstruction, 961.72
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INTRODUCTION
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Magnetic resonance (MR) angiography is rapidly becoming the standard noninvasive diagnostic imaging examination for evaluation of renal artery stenosis. In particular, dynamic gadolinium-enhanced MR angiography (1–9) and three-dimensional (3D) phase-contrast (PC) MR angiography (9–12) reliably demonstrate the degree of arterial stenosis and its hemodynamic significance. However, the MR angiographic findings after renal artery revascularization are not as well characterized. Use of gadolinium-enhanced MR angiography after renal artery revascularization to detect markers of technical and clinical success has been evaluated in a small series of patients (13).
In this article, we describe our clinical experience with a specific subpopulation of patients undergoing MR angiography after renal artery revascularization and the MR angiography techniques used to study these individuals. In addition, the expected anatomic results and complications of renal artery revascularization are presented.
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CLINICAL EXPERIENCE
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Patient Population
Fifteen patients (10 men, five women; mean age, 63 years; age range, 43–74 years) underwent gadolinium-enhanced MR angiography after renal artery revascularization. Indications for study included increased or persistent hypertension alone (n = 2), hypertension and persistent elevation of creatinine level (n = 4), evaluation of renal arterial flow (n = 2), and routine postintervention follow-up (n = 7).
MR Angiography Technique
All studies were performed with a 1.5-T unit (Signa; GE Medical Systems, Milwaukee, Wis) with a body coil used for signal transmission and reception. Four pulse sequences made up the standard renal artery examination (Table): sagittal T1-weighted localization, axial T2-weighted fast spin-echo with fat saturation, breath-hold coronal 3D dynamic gadolinium-enhanced MR angiography, and axial 3D PC MR angiography. For the 3D gadolinium-enhanced MR angiography, the section thickness, number of coronal sections, and number of phase-encoding steps varied according to the patient's breath-holding ability and the volume coverage required. Because surgical techniques for revascularization vary, knowledge of the surgical procedure is necessary to ensure inclusion of the pertinent anatomy within the 3D gadolinium-enhanced MR angiography volume and to define the appropriate 3D PC MR angiography volume. The specific parameters used at our institution are summarized in the Table. The image acquisition time for gadolinium-enhanced MR angiography was typically 25 seconds (range, 15–58 seconds).
The dose of gadolinium contrast material (gadodiamide [Omniscan; Nycomed, Princeton, NJ] or gadopentetate dimeglumine [Magnevist; Berlex Laboratories, Wayne, NJ]) was standardized to 42 mL (21 mmol) in patients weighing less than 95 kg. For patients weighing more than 95 kg, 63 mL (32 mmol) was used. Contrast material was administered by means of manual injection at a rate of 2–3 mL/sec through a 20- or 22-gauge peripheral intravenous catheter with a 2-m-long connector tubing set (SmartSet; TopSpins, Ann Arbor, Mich), which was equipped with one-way valves to prevent admixing of contrast material and flushing saline solution. The timing of the bolus injection was optimized with an automated triggering pulse sequence (SmartPrep; GE Medical Systems).
Triggered 3D gadolinium-enhanced MR angiography was prescribed from a parasagittal image that showed the abdominal aorta at the level of the celiac trunk and superior mesenteric artery. The trigger was placed over the posterior aspect of the abdominal aorta (trigger volume length = 10 cm, trigger volume width = 40 mm, max monitor = 30, image acquisition delay = 5 seconds, Special = 0, 512 ZIP = 0, Slice Zip = 2). Alternatively, an empiric imaging delay of 10 seconds after the start of contrast material injection may be used. For patients anticipated to have slow flow, the imaging delay may be increased to 15 seconds. A series of three breath-held 3D gadolinium-enhanced MR angiography volumes was acquired, with each volumetric acquisition separated by a rest period of approximately 10–15 seconds.
All images were reviewed on a computer workstation (Advantage Windows; GE Medical Systems). Coronal source images from 3D gadolinium-enhanced MR angiography and axial source images from 3D PC MR angiography were reconstructed by using multiple operator-defined maximum-intensity projection (MIP) images. In particular, the 3D gadolinium-enhanced MR angiography volume was manipulated to view relevant vascular anatomy at the optimal obliquity and section thickness.
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EXPECTED ANATOMIC RESULTS OF RENAL ARTERY REVASCULARIZATION
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At our institution, renal artery reconstruction is accomplished with a variety of techniques, including percutaneous transluminal angioplasty (Fig 1) and Palmaz stent placement. If a stent is placed in the renal artery, postrevascularization MR angiography may be limited by field inhomogeneity artifact from the metal stent (Fig 2).
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Figure 1a. Bilateral renal artery stenosis in a 65-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows bilateral renal artery stenosis (arrows). (b) Axial 3D PC image shows signal dropout (arrows), which indicates hemodynamic significance (1). (c) Axial PC image obtained after bilateral percutaneous angioplasty shows diminished spin dephasing, which is consistent with improved flow to the kidneys. (d-f) Coronal (d) and axial (e, f) subvolume MIP images obtained after renal artery revascularization show increased caliber of both renal arteries. Minimal residual narrowing of the left renal artery origin is seen (d, f); however, the PC image (f) shows no residual spin dephasing to suggest hemodynamic significance. The postrevascularization gadolinium-enhanced MR angiography volume (d) was acquired with a longer delay after contrast material infusion, which accounts for the better visualization of the left renal vein (L) and portal vein (P).
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Figure 1b. Bilateral renal artery stenosis in a 65-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows bilateral renal artery stenosis (arrows). (b) Axial 3D PC image shows signal dropout (arrows), which indicates hemodynamic significance (1). (c) Axial PC image obtained after bilateral percutaneous angioplasty shows diminished spin dephasing, which is consistent with improved flow to the kidneys. (d-f) Coronal (d) and axial (e, f) subvolume MIP images obtained after renal artery revascularization show increased caliber of both renal arteries. Minimal residual narrowing of the left renal artery origin is seen (d, f); however, the PC image (f) shows no residual spin dephasing to suggest hemodynamic significance. The postrevascularization gadolinium-enhanced MR angiography volume (d) was acquired with a longer delay after contrast material infusion, which accounts for the better visualization of the left renal vein (L) and portal vein (P).
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Figure 1c. Bilateral renal artery stenosis in a 65-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows bilateral renal artery stenosis (arrows). (b) Axial 3D PC image shows signal dropout (arrows), which indicates hemodynamic significance (1). (c) Axial PC image obtained after bilateral percutaneous angioplasty shows diminished spin dephasing, which is consistent with improved flow to the kidneys. (d-f) Coronal (d) and axial (e, f) subvolume MIP images obtained after renal artery revascularization show increased caliber of both renal arteries. Minimal residual narrowing of the left renal artery origin is seen (d, f); however, the PC image (f) shows no residual spin dephasing to suggest hemodynamic significance. The postrevascularization gadolinium-enhanced MR angiography volume (d) was acquired with a longer delay after contrast material infusion, which accounts for the better visualization of the left renal vein (L) and portal vein (P).
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Figure 1d. Bilateral renal artery stenosis in a 65-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows bilateral renal artery stenosis (arrows). (b) Axial 3D PC image shows signal dropout (arrows), which indicates hemodynamic significance (1). (c) Axial PC image obtained after bilateral percutaneous angioplasty shows diminished spin dephasing, which is consistent with improved flow to the kidneys. (d-f) Coronal (d) and axial (e, f) subvolume MIP images obtained after renal artery revascularization show increased caliber of both renal arteries. Minimal residual narrowing of the left renal artery origin is seen (d, f); however, the PC image (f) shows no residual spin dephasing to suggest hemodynamic significance. The postrevascularization gadolinium-enhanced MR angiography volume (d) was acquired with a longer delay after contrast material infusion, which accounts for the better visualization of the left renal vein (L) and portal vein (P).
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Figure 1e. Bilateral renal artery stenosis in a 65-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows bilateral renal artery stenosis (arrows). (b) Axial 3D PC image shows signal dropout (arrows), which indicates hemodynamic significance (1). (c) Axial PC image obtained after bilateral percutaneous angioplasty shows diminished spin dephasing, which is consistent with improved flow to the kidneys. (d-f) Coronal (d) and axial (e, f) subvolume MIP images obtained after renal artery revascularization show increased caliber of both renal arteries. Minimal residual narrowing of the left renal artery origin is seen (d, f); however, the PC image (f) shows no residual spin dephasing to suggest hemodynamic significance. The postrevascularization gadolinium-enhanced MR angiography volume (d) was acquired with a longer delay after contrast material infusion, which accounts for the better visualization of the left renal vein (L) and portal vein (P).
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Figure 1f. Bilateral renal artery stenosis in a 65-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows bilateral renal artery stenosis (arrows). (b) Axial 3D PC image shows signal dropout (arrows), which indicates hemodynamic significance (1). (c) Axial PC image obtained after bilateral percutaneous angioplasty shows diminished spin dephasing, which is consistent with improved flow to the kidneys. (d-f) Coronal (d) and axial (e, f) subvolume MIP images obtained after renal artery revascularization show increased caliber of both renal arteries. Minimal residual narrowing of the left renal artery origin is seen (d, f); however, the PC image (f) shows no residual spin dephasing to suggest hemodynamic significance. The postrevascularization gadolinium-enhanced MR angiography volume (d) was acquired with a longer delay after contrast material infusion, which accounts for the better visualization of the left renal vein (L) and portal vein (P).
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Figure 2a. Unilateral renal artery stenosis in a 67-year-old man after percutaneous transluminal angioplasty and Palmaz stent placement. (a) Axial T2-weighted MR image at the level of the right renal artery origin shows an oval region of signal dropout with an irregular halo of intense brightness (arrow), which indicates the presence of a metallic stent. (b) Coronal subvolume MIP image from gadolinium-enhanced MR angiography shows the signal dropout (arrow), which limits full evaluation of the revascularized renal artery.
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Figure 2b. Unilateral renal artery stenosis in a 67-year-old man after percutaneous transluminal angioplasty and Palmaz stent placement. (a) Axial T2-weighted MR image at the level of the right renal artery origin shows an oval region of signal dropout with an irregular halo of intense brightness (arrow), which indicates the presence of a metallic stent. (b) Coronal subvolume MIP image from gadolinium-enhanced MR angiography shows the signal dropout (arrow), which limits full evaluation of the revascularized renal artery.
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The appearance of the renal arteries before and after aortorenal endarterectomy is revealing with regard to imaging technique and image manipulation (Figs 3, 4). The added usefulness of postprocessing the coronal source images from gadolinium-enhanced MR angiography is shown in Figure 3. In a 3D sum of all coronal images in the volume, the more anteriorly located superior mesenteric artery projects over the left renal artery, obscuring the proximal renal artery (Fig 3a). Reconstruction of a thinner subvolume MIP image excludes the superior mesenteric artery and displays the renal arteries completely without additional image acquisition or further contrast material administration (Fig 3b).
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Figure 3a. Bilateral renal artery stenosis in a 43-year-old man. (a) Coronal arterial-phase 3D MIP image shows an irregular aorta with mural plaque. Focal segmental stenoses affect the right and left common iliac arteries and the left external iliac artery. The right renal artery is nearly occluded at its origin (arrow). The proximal superior mesenteric artery (black arrowhead) obscures the left renal artery (white arrowhead). (b) Coronal subvolume MIP image centered at the renal arteries shows severe bilateral renal artery stenosis. (c) Coronal MR image obtained after aortorenal endarterectomy shows increased renal artery caliber and an improved aortic contour.
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Figure 3b. Bilateral renal artery stenosis in a 43-year-old man. (a) Coronal arterial-phase 3D MIP image shows an irregular aorta with mural plaque. Focal segmental stenoses affect the right and left common iliac arteries and the left external iliac artery. The right renal artery is nearly occluded at its origin (arrow). The proximal superior mesenteric artery (black arrowhead) obscures the left renal artery (white arrowhead). (b) Coronal subvolume MIP image centered at the renal arteries shows severe bilateral renal artery stenosis. (c) Coronal MR image obtained after aortorenal endarterectomy shows increased renal artery caliber and an improved aortic contour.
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Figure 3c. Bilateral renal artery stenosis in a 43-year-old man. (a) Coronal arterial-phase 3D MIP image shows an irregular aorta with mural plaque. Focal segmental stenoses affect the right and left common iliac arteries and the left external iliac artery. The right renal artery is nearly occluded at its origin (arrow). The proximal superior mesenteric artery (black arrowhead) obscures the left renal artery (white arrowhead). (b) Coronal subvolume MIP image centered at the renal arteries shows severe bilateral renal artery stenosis. (c) Coronal MR image obtained after aortorenal endarterectomy shows increased renal artery caliber and an improved aortic contour.
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Figure 4a. Bilateral renal artery stenosis in a 59-year-old man. (a, b) Sagittal (a) and coronal (b) MR images show a complex perirenal abdominal aortic aneurysm, which terminates 2 cm above the iliac bifurcation. Both proximal renal arteries are severely stenosed (arrows); the celiac artery (C) and superior mesenteric artery (S) are patent. (c) Coronal MR image obtained after aneurysmectomy and bilateral aortorenal endarterectomy shows increased caliber of the proximal renal arteries. The diseased infrarenal aorta was replaced by a graft (G), with residual dilatation of the perirenal aorta (arrowhead).
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Figure 4b. Bilateral renal artery stenosis in a 59-year-old man. (a, b) Sagittal (a) and coronal (b) MR images show a complex perirenal abdominal aortic aneurysm, which terminates 2 cm above the iliac bifurcation. Both proximal renal arteries are severely stenosed (arrows); the celiac artery (C) and superior mesenteric artery (S) are patent. (c) Coronal MR image obtained after aneurysmectomy and bilateral aortorenal endarterectomy shows increased caliber of the proximal renal arteries. The diseased infrarenal aorta was replaced by a graft (G), with residual dilatation of the perirenal aorta (arrowhead).
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Figure 4c. Bilateral renal artery stenosis in a 59-year-old man. (a, b) Sagittal (a) and coronal (b) MR images show a complex perirenal abdominal aortic aneurysm, which terminates 2 cm above the iliac bifurcation. Both proximal renal arteries are severely stenosed (arrows); the celiac artery (C) and superior mesenteric artery (S) are patent. (c) Coronal MR image obtained after aneurysmectomy and bilateral aortorenal endarterectomy shows increased caliber of the proximal renal arteries. The diseased infrarenal aorta was replaced by a graft (G), with residual dilatation of the perirenal aorta (arrowhead).
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The adequacy of aortorenal bypass grafts is evident on MR angiograms routinely obtained as part of the postoperative follow-up (Figs 5 –7). Complex vascular anatomy after extraanatomic bypass, including splenorenal bypass (Fig 8) and gastroduodenal-renal bypass (Fig 9), may also be accurately demonstrated with gadolinium-enhanced MR angiography. The multiplanar reformatting capability of gadolinium-enhanced MR angiography allows clear visualization of such reconstructions.
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Figure 5a. Normal findings in a 51-year-old man after bilateral aortorenal bypass for renal artery stenosis. (a) Coronal subvolume MIP image from gadolinium-enhanced MR angiography shows patency of both bypass grafts with minor irregularity of the distal anastomosis on the right (arrow). (b) Coronal 3D PC image shows patent bypass grafts with no flow disturbance at the site of anastomotic irregularity (arrowhead). I = inferior vena cava.
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Figure 5b. Normal findings in a 51-year-old man after bilateral aortorenal bypass for renal artery stenosis. (a) Coronal subvolume MIP image from gadolinium-enhanced MR angiography shows patency of both bypass grafts with minor irregularity of the distal anastomosis on the right (arrow). (b) Coronal 3D PC image shows patent bypass grafts with no flow disturbance at the site of anastomotic irregularity (arrowhead). I = inferior vena cava.
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Figure 6a. Renal artery stenosis in a 74-year-old man who had undergone left nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows severe right renal artery stenosis (arrow). (b) Coronal subvolume MIP image shows the anatomy after placement of an aortorenal bypass graft (arrow). IMA = inferior mesenteric artery.
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Figure 6b. Renal artery stenosis in a 74-year-old man who had undergone left nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows severe right renal artery stenosis (arrow). (b) Coronal subvolume MIP image shows the anatomy after placement of an aortorenal bypass graft (arrow). IMA = inferior mesenteric artery.
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Figure 7a. Bilateral fibromuscular dysplasia of the renal arteries in a 51-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows beading of both distal renal arteries (arrowheads). Note the focal narrowing of the proximal left renal artery (arrow). (b) Axial 3D PC image shows spin dephasing (arrow), which is suggestive of hemodynamic significance. There is also signal dropout in the segmentally stenosed distal renal arteries due to turbulent flow. (c) Coronal gadolinium-enhanced MR angiogram obtained after bilateral aortorenal bypass shows the grafts. Arrowhead = stump of native right renal artery. (d-f) Sequential axial 3D PC images (presented from superior [d] to inferior [f]) show no flow disturbance. Note that the right renal graft (arrow) originates anterior to the inferior vena cava (I) and inferior to the left renal vein (L).
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Figure 7b. Bilateral fibromuscular dysplasia of the renal arteries in a 51-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows beading of both distal renal arteries (arrowheads). Note the focal narrowing of the proximal left renal artery (arrow). (b) Axial 3D PC image shows spin dephasing (arrow), which is suggestive of hemodynamic significance. There is also signal dropout in the segmentally stenosed distal renal arteries due to turbulent flow. (c) Coronal gadolinium-enhanced MR angiogram obtained after bilateral aortorenal bypass shows the grafts. Arrowhead = stump of native right renal artery. (d-f) Sequential axial 3D PC images (presented from superior [d] to inferior [f]) show no flow disturbance. Note that the right renal graft (arrow) originates anterior to the inferior vena cava (I) and inferior to the left renal vein (L).
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Figure 7c. Bilateral fibromuscular dysplasia of the renal arteries in a 51-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows beading of both distal renal arteries (arrowheads). Note the focal narrowing of the proximal left renal artery (arrow). (b) Axial 3D PC image shows spin dephasing (arrow), which is suggestive of hemodynamic significance. There is also signal dropout in the segmentally stenosed distal renal arteries due to turbulent flow. (c) Coronal gadolinium-enhanced MR angiogram obtained after bilateral aortorenal bypass shows the grafts. Arrowhead = stump of native right renal artery. (d-f) Sequential axial 3D PC images (presented from superior [d] to inferior [f]) show no flow disturbance. Note that the right renal graft (arrow) originates anterior to the inferior vena cava (I) and inferior to the left renal vein (L).
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Figure 7d. Bilateral fibromuscular dysplasia of the renal arteries in a 51-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows beading of both distal renal arteries (arrowheads). Note the focal narrowing of the proximal left renal artery (arrow). (b) Axial 3D PC image shows spin dephasing (arrow), which is suggestive of hemodynamic significance. There is also signal dropout in the segmentally stenosed distal renal arteries due to turbulent flow. (c) Coronal gadolinium-enhanced MR angiogram obtained after bilateral aortorenal bypass shows the grafts. Arrowhead = stump of native right renal artery. (d-f) Sequential axial 3D PC images (presented from superior [d] to inferior [f]) show no flow disturbance. Note that the right renal graft (arrow) originates anterior to the inferior vena cava (I) and inferior to the left renal vein (L).
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Figure 7e. Bilateral fibromuscular dysplasia of the renal arteries in a 51-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows beading of both distal renal arteries (arrowheads). Note the focal narrowing of the proximal left renal artery (arrow). (b) Axial 3D PC image shows spin dephasing (arrow), which is suggestive of hemodynamic significance. There is also signal dropout in the segmentally stenosed distal renal arteries due to turbulent flow. (c) Coronal gadolinium-enhanced MR angiogram obtained after bilateral aortorenal bypass shows the grafts. Arrowhead = stump of native right renal artery. (d-f) Sequential axial 3D PC images (presented from superior [d] to inferior [f]) show no flow disturbance. Note that the right renal graft (arrow) originates anterior to the inferior vena cava (I) and inferior to the left renal vein (L).
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Figure 7f. Bilateral fibromuscular dysplasia of the renal arteries in a 51-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows beading of both distal renal arteries (arrowheads). Note the focal narrowing of the proximal left renal artery (arrow). (b) Axial 3D PC image shows spin dephasing (arrow), which is suggestive of hemodynamic significance. There is also signal dropout in the segmentally stenosed distal renal arteries due to turbulent flow. (c) Coronal gadolinium-enhanced MR angiogram obtained after bilateral aortorenal bypass shows the grafts. Arrowhead = stump of native right renal artery. (d-f) Sequential axial 3D PC images (presented from superior [d] to inferior [f]) show no flow disturbance. Note that the right renal graft (arrow) originates anterior to the inferior vena cava (I) and inferior to the left renal vein (L).
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Figure 8a. Unilateral renal artery stenosis in a 64-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows severe left renal artery stenosis (solid arrow). The irregularity of the distal aorta (open arrow) represents incomplete enhancement of a severely atherosclerotic infrarenal aneurysm. (b) Coronal gadolinium-enhanced MR angiogram obtained after splenorenal bypass shows the graft (arrow). (c) Oblique reconstruction image obtained parallel to the course of the graft shows the anastomosis most accurately (arrow). GD = gastroduodenal artery, H = common hepatic artery, R = right renal artery, S = superior mesenteric artery, Spl = splenic artery.
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Figure 8b. Unilateral renal artery stenosis in a 64-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows severe left renal artery stenosis (solid arrow). The irregularity of the distal aorta (open arrow) represents incomplete enhancement of a severely atherosclerotic infrarenal aneurysm. (b) Coronal gadolinium-enhanced MR angiogram obtained after splenorenal bypass shows the graft (arrow). (c) Oblique reconstruction image obtained parallel to the course of the graft shows the anastomosis most accurately (arrow). GD = gastroduodenal artery, H = common hepatic artery, R = right renal artery, S = superior mesenteric artery, Spl = splenic artery.
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Figure 8c. Unilateral renal artery stenosis in a 64-year-old woman. (a) Coronal gadolinium-enhanced MR angiogram shows severe left renal artery stenosis (solid arrow). The irregularity of the distal aorta (open arrow) represents incomplete enhancement of a severely atherosclerotic infrarenal aneurysm. (b) Coronal gadolinium-enhanced MR angiogram obtained after splenorenal bypass shows the graft (arrow). (c) Oblique reconstruction image obtained parallel to the course of the graft shows the anastomosis most accurately (arrow). GD = gastroduodenal artery, H = common hepatic artery, R = right renal artery, S = superior mesenteric artery, Spl = splenic artery.
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Figure 9a. Renal artery stenosis in a 65-year-old woman who had undergone left nephrectomy. (a) Coronal subvolume MIP image shows severe right renal artery stenosis (arrow). (b) Coronal subvolume MIP image obtained after gastroduodenal-renal bypass does not clearly show the anastomosis (arrow) due to the coronal projection. (c) Oblique MIP image obtained in the plane of the graft shows the anastomosis (arrow). GD = gastroduodenal artery, H = proper hepatic artery, S = superior mesenteric artery.
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Figure 9b. Renal artery stenosis in a 65-year-old woman who had undergone left nephrectomy. (a) Coronal subvolume MIP image shows severe right renal artery stenosis (arrow). (b) Coronal subvolume MIP image obtained after gastroduodenal-renal bypass does not clearly show the anastomosis (arrow) due to the coronal projection. (c) Oblique MIP image obtained in the plane of the graft shows the anastomosis (arrow). GD = gastroduodenal artery, H = proper hepatic artery, S = superior mesenteric artery.
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Figure 9c. Renal artery stenosis in a 65-year-old woman who had undergone left nephrectomy. (a) Coronal subvolume MIP image shows severe right renal artery stenosis (arrow). (b) Coronal subvolume MIP image obtained after gastroduodenal-renal bypass does not clearly show the anastomosis (arrow) due to the coronal projection. (c) Oblique MIP image obtained in the plane of the graft shows the anastomosis (arrow). GD = gastroduodenal artery, H = proper hepatic artery, S = superior mesenteric artery.
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COMPLICATIONS OF RENAL ARTERY REVASCULARIZATION
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Vascular thromboses in the period immediately after revascularization are readily demonstrated with MR angiography (Fig 10). Acute renal artery thrombosis after endarterectomy occurs in 2% of patients (14) and typically manifests as persistent or recurrent hypertension. Hematuria may accompany the hypertension if the renal artery thrombosis is complicated by thromboembolism to the kidney parenchyma itself. Thrombosis rates of 2%–14% after renal artery graft placement have been reported (15).
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Figure 10a. Thrombosis in a 65-year-old man with anuria and increased creatinine level 2 days after aortobifemoral bypass and bilateral aortorenal endarterectomy. (a) Coronal gadolinium-enhanced MR angiogram shows acute thrombosis of the right renal artery (arrow). (b) Oblique MIP image shows extension of the thrombosis into the aorta (arrow). (c, d) Oblique MR images show peripheral perfusion defects in both kidneys (arrowhead), which indicate renal parenchymal infarcts. (Fig 10a reprinted, with permission, from reference 13.)
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Figure 10b. Thrombosis in a 65-year-old man with anuria and increased creatinine level 2 days after aortobifemoral bypass and bilateral aortorenal endarterectomy. (a) Coronal gadolinium-enhanced MR angiogram shows acute thrombosis of the right renal artery (arrow). (b) Oblique MIP image shows extension of the thrombosis into the aorta (arrow). (c, d) Oblique MR images show peripheral perfusion defects in both kidneys (arrowhead), which indicate renal parenchymal infarcts. (Fig 10a reprinted, with permission, from reference 13.)
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Figure 10c. Thrombosis in a 65-year-old man with anuria and increased creatinine level 2 days after aortobifemoral bypass and bilateral aortorenal endarterectomy. (a) Coronal gadolinium-enhanced MR angiogram shows acute thrombosis of the right renal artery (arrow). (b) Oblique MIP image shows extension of the thrombosis into the aorta (arrow). (c, d) Oblique MR images show peripheral perfusion defects in both kidneys (arrowhead), which indicate renal parenchymal infarcts. (Fig 10a reprinted, with permission, from reference 13.)
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Figure 10d. Thrombosis in a 65-year-old man with anuria and increased creatinine level 2 days after aortobifemoral bypass and bilateral aortorenal endarterectomy. (a) Coronal gadolinium-enhanced MR angiogram shows acute thrombosis of the right renal artery (arrow). (b) Oblique MIP image shows extension of the thrombosis into the aorta (arrow). (c, d) Oblique MR images show peripheral perfusion defects in both kidneys (arrowhead), which indicate renal parenchymal infarcts. (Fig 10a reprinted, with permission, from reference 13.)
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Postoperative bleeding may also be demonstrated with MR angiography (Fig 11). Gadolinium-enhanced MR angiography permits rapid serial acquisitions over the same imaging volume without any ionizing radiation and allows dynamic imaging of the kidneys in the arterial, venous, and delayed phases.
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Figure 11a. Hemorrhage in a 68-year-old woman with decreased hematocrit and decreased urine output 7 days after infrarenal aortobifemoral bypass, left aortorenal bypass, and right nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows patency of the aortorenal graft (arrow). (b, c) Sagittal T1-weighted (b) and contrast material-enhanced axial fat-saturated T1-weighted (c) MR images show a fluid collection with heterogeneous signal intensity (arrow). The fluid collection is indicative of subcapsular and perirenal hemorrhage. (d-f) Arterial-phase (d), venous-phase (e), and delayed-phase (f) coronal MR images show extrarenal accumulation of contrast material, which represents active bleeding.
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Figure 11b. Hemorrhage in a 68-year-old woman with decreased hematocrit and decreased urine output 7 days after infrarenal aortobifemoral bypass, left aortorenal bypass, and right nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows patency of the aortorenal graft (arrow). (b, c) Sagittal T1-weighted (b) and contrast material-enhanced axial fat-saturated T1-weighted (c) MR images show a fluid collection with heterogeneous signal intensity (arrow). The fluid collection is indicative of subcapsular and perirenal hemorrhage. (d-f) Arterial-phase (d), venous-phase (e), and delayed-phase (f) coronal MR images show extrarenal accumulation of contrast material, which represents active bleeding.
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Figure 11c. Hemorrhage in a 68-year-old woman with decreased hematocrit and decreased urine output 7 days after infrarenal aortobifemoral bypass, left aortorenal bypass, and right nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows patency of the aortorenal graft (arrow). (b, c) Sagittal T1-weighted (b) and contrast material-enhanced axial fat-saturated T1-weighted (c) MR images show a fluid collection with heterogeneous signal intensity (arrow). The fluid collection is indicative of subcapsular and perirenal hemorrhage. (d-f) Arterial-phase (d), venous-phase (e), and delayed-phase (f) coronal MR images show extrarenal accumulation of contrast material, which represents active bleeding.
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Figure 11d. Hemorrhage in a 68-year-old woman with decreased hematocrit and decreased urine output 7 days after infrarenal aortobifemoral bypass, left aortorenal bypass, and right nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows patency of the aortorenal graft (arrow). (b, c) Sagittal T1-weighted (b) and contrast material-enhanced axial fat-saturated T1-weighted (c) MR images show a fluid collection with heterogeneous signal intensity (arrow). The fluid collection is indicative of subcapsular and perirenal hemorrhage. (d-f) Arterial-phase (d), venous-phase (e), and delayed-phase (f) coronal MR images show extrarenal accumulation of contrast material, which represents active bleeding.
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Figure 11e. Hemorrhage in a 68-year-old woman with decreased hematocrit and decreased urine output 7 days after infrarenal aortobifemoral bypass, left aortorenal bypass, and right nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows patency of the aortorenal graft (arrow). (b, c) Sagittal T1-weighted (b) and contrast material-enhanced axial fat-saturated T1-weighted (c) MR images show a fluid collection with heterogeneous signal intensity (arrow). The fluid collection is indicative of subcapsular and perirenal hemorrhage. (d-f) Arterial-phase (d), venous-phase (e), and delayed-phase (f) coronal MR images show extrarenal accumulation of contrast material, which represents active bleeding.
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Figure 11f. Hemorrhage in a 68-year-old woman with decreased hematocrit and decreased urine output 7 days after infrarenal aortobifemoral bypass, left aortorenal bypass, and right nephrectomy. (a) Coronal gadolinium-enhanced MR angiogram shows patency of the aortorenal graft (arrow). (b, c) Sagittal T1-weighted (b) and contrast material-enhanced axial fat-saturated T1-weighted (c) MR images show a fluid collection with heterogeneous signal intensity (arrow). The fluid collection is indicative of subcapsular and perirenal hemorrhage. (d-f) Arterial-phase (d), venous-phase (e), and delayed-phase (f) coronal MR images show extrarenal accumulation of contrast material, which represents active bleeding.
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Identification of postprocedure dissection depends on demonstration of the dissection flap as a linear filling defect within the vessel lumen. In this situation, gadolinium-enhanced MR angiograms may be misleading (Fig 12) due to a potential pitfall of MIP, a technique in which the brightest voxel along a ray in a 3D volume is displayed in a two-dimensional projection. Consequently, subtle filling defects such as a dissection flap may be obscured. If a filling defect is suspected, diagnostic sensitivity may be improved by using sequential thin subvolume MIP reconstruction images or average- or minimum-intensity projection, which projects the average or minimum voxel signal along a ray.
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Figure 12a. Aortic dissection in a 59-year-old man after bilateral endarterectomy of the main renal arteries and accessory renal arteries. (a) Coronal 3D MIP image from gadolinium-enhanced MR angiography shows bilateral renal artery stenosis (arrows) and bilateral accessory renal arteries (arrowheads). (b) Postrevascularization coronal 3D MIP image from gadolinium-enhanced MR angiography shows a dissection of the infrarenal aorta as a subtle linear filling defect with associated mural contour deformity (arrow). Arrowheads = accessory renal arteries.
(c) Coronal 5-mm-thick MIP subvolume reconstruction image shows the extent of the dissection flap (arrow). The dissection was treated with a Wallstent.
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Figure 12b. Aortic dissection in a 59-year-old man after bilateral endarterectomy of the main renal arteries and accessory renal arteries. (a) Coronal 3D MIP image from gadolinium-enhanced MR angiography shows bilateral renal artery stenosis (arrows) and bilateral accessory renal arteries (arrowheads). (b) Postrevascularization coronal 3D MIP image from gadolinium-enhanced MR angiography shows a dissection of the infrarenal aorta as a subtle linear filling defect with associated mural contour deformity (arrow). Arrowheads = accessory renal arteries.
(c) Coronal 5-mm-thick MIP subvolume reconstruction image shows the extent of the dissection flap (arrow). The dissection was treated with a Wallstent.
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Figure 12c. Aortic dissection in a 59-year-old man after bilateral endarterectomy of the main renal arteries and accessory renal arteries. (a) Coronal 3D MIP image from gadolinium-enhanced MR angiography shows bilateral renal artery stenosis (arrows) and bilateral accessory renal arteries (arrowheads). (b) Postrevascularization coronal 3D MIP image from gadolinium-enhanced MR angiography shows a dissection of the infrarenal aorta as a subtle linear filling defect with associated mural contour deformity (arrow). Arrowheads = accessory renal arteries.
(c) Coronal 5-mm-thick MIP subvolume reconstruction image shows the extent of the dissection flap (arrow). The dissection was treated with a Wallstent.
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Aneurysms and pseudoaneurysms of aortorenal (Fig 13) or iliorenal (Fig 14) grafts occur in less than 6% of patients, although nonprogressive, uniform increases in the diameter of saphenous vein grafts have been reported in 20%–44% of cases (14). Hemodynamically significant recurrent stenoses of a revascularized renal artery occur in 8% of vein grafts but are unusual after endarterectomy and arterial autografting.
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Figure 13. Bypass graft pseudoaneurysm in a 66-year-old man after left aortorenal bypass. Arterial-phase coronal gadolinium-enhanced MR angiogram shows a pseudoaneurysm at the orifice of the graft (straight arrow). Note the near occlusion of the right renal artery (small arrowhead). The right common iliac artery is occluded beyond its origin (large arrowhead). The left external iliac artery is segmentally stenosed (curved arrow).
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Figure 14a. Bypass graft pseudoaneurysms in a 70-year-old man with recurrent hypertension 10 years after right iliorenal bypass. (a) Coronal 3D MIP image shows pseudoaneurysms of the proximal and distal aspects of the graft; however, the size of the dilated segments is underestimated. (b-d) Coronal subvolume MIP image (b) and axial subvolume MIP images reconstructed at the level of the superior graft anastomosis (c) and inferior graft anastomosis (d) show the true extent of the dilatation, including areas of thrombosis (arrows).
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Figure 14b. Bypass graft pseudoaneurysms in a 70-year-old man with recurrent hypertension 10 years after right iliorenal bypass. (a) Coronal 3D MIP image shows pseudoaneurysms of the proximal and distal aspects of the graft; however, the size of the dilated segments is underestimated. (b-d) Coronal subvolume MIP image (b) and axial subvolume MIP images reconstructed at the level of the superior graft anastomosis (c) and inferior graft anastomosis (d) show the true extent of the dilatation, including areas of thrombosis (arrows).
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Figure 14c. Bypass graft pseudoaneurysms in a 70-year-old man with recurrent hypertension 10 years after right iliorenal bypass. (a) Coronal 3D MIP image shows pseudoaneurysms of the proximal and distal aspects of the graft; however, the size of the dilated segments is underestimated. (b-d) Coronal subvolume MIP image (b) and axial subvolume MIP images reconstructed at the level of the superior graft anastomosis (c) and inferior graft anastomosis (d) show the true extent of the dilatation, including areas of thrombosis (arrows).
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Figure 14d. Bypass graft pseudoaneurysms in a 70-year-old man with recurrent hypertension 10 years after right iliorenal bypass. (a) Coronal 3D MIP image shows pseudoaneurysms of the proximal and distal aspects of the graft; however, the size of the dilated segments is underestimated. (b-d) Coronal subvolume MIP image (b) and axial subvolume MIP images reconstructed at the level of the superior graft anastomosis (c) and inferior graft anastomosis (d) show the true extent of the dilatation, including areas of thrombosis (arrows).
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Although not usually considered a direct complication, accelerated renal artery stenosis after percutaneous transluminal angioplasty (Fig 15) is the most common untoward sequela of this procedure.
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Figure 15a. Right renal artery occlusion and left renal artery stenosis in a 72-year-old man after percutaneous transluminal angioplasty of the left renal artery. (a) Conventional angiogram shows residual stenosis of the left renal artery (arrow). However, no pressure gradient could be demonstrated immediately after angioplasty. Eleven months later, the patient experienced gradually increasing hypertension refractory to medication and slowly worsening renal function. (b) Coronal subvolume MIP image from gadolinium-enhanced MR angiography shows progression of the left renal artery stenosis to near occlusion (arrow). The right renal artery remains occluded. (c) Axial PC image shows signal dropout at the site of the stenosis (arrowhead) with a jet of dephasing distal to the stenosis.
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Figure 15b. Right renal artery occlusion and left renal artery stenosis in a 72-year-old man after percutaneous transluminal angioplasty of the left renal artery. (a) Conventional angiogram shows residual stenosis of the left renal artery (arrow). However, no pressure gradient could be demonstrated immediately after angioplasty. Eleven months later, the patient experienced gradually increasing hypertension refractory to medication and slowly worsening renal function. (b) Coronal subvolume MIP image from gadolinium-enhanced MR angiography shows progression of the left renal artery stenosis to near occlusion (arrow). The right renal artery remains occluded. (c) Axial PC image shows signal dropout at the site of the stenosis (arrowhead) with a jet of dephasing distal to the stenosis.
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Abstract
INTRODUCTION
