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RENAL REVASCULARIZATION

RENAL REVASCULARIZATION

Renal artery stenosis (RAS) is defined as an anatomic narrowing of the main renal artery or its segmental branches, which can lead to secondary renovascular hypertension (RVH) and renal failure if sufficiently advanced. The pathophysiology and diagnosis of this lesion are demonstrated in Plates 4-36 and 4-37. Briefly, the major causes are atherosclerosis, which accounts for about 90% of cases, and fibromuscular dysplasia (FMD), which accounts for most of the remainder. Atherosclerosis, which tends to occur in older individuals with classic risk factors, involves the intimal layer of the artery and develops circumferentially to occlude a progressive fraction of the vessel lumen. FMD, in contrast, causes collagenous dysplasia of either the intimal or medial arterial layers.

 

ENDOVASCULAR THERAPIES FOR RENAL ARTERY STENOSIS
Plate 10-17
ENDOVASCULAR THERAPIES FOR RENAL ARTERY STENOSIS

INDICATIONS AND EVALUATIONS

The initial management of RVH secondary to RAS is with antihypertensive medications, especially ACE inhibitors. The need for surgical intervention depends on the patient’s response to antihypertensive medications and the degree (if any) of renal insufficiency. Renal revascularization may be considered if blood pressure is refractory to treatment with multiple agents, or if patients have bilateral stenosis or stenosis of a solitary kidney. In the latter group, revascularization offers the most benefit if there is no intrinsic renal disease and renal function is either intact or only mildly impaired. The resistive index, measured on ultrasound, provides some indication of the degree of renal parenchymal fibrosis, and it has been shown to predict the degree of benefit following intervention.

When revascularization is being considered, preoperative assessment depends on the cause of the vascular lesion. Patients with FMD are generally young and in otherwise good health. Patients with atherosclerosis, in contrast, are likely to have disease elsewhere in the vasculature and are thus at increased risk for postoperative myocardial infarction and/or cerebrovascular accident. Therefore, such patients should undergo thorough preoperative evaluation, which may include cardiac stress testing and/or carotid ultrasound.

 

PROCEDURE

Endovascular repair has become the preferred method for renal revascularization. Open surgical repair, in contrast, is typically reserved for patients who have failed endovascular repair, who have comorbidities such as aortic or renal artery aneurysms, or who have large and complex lesions.

Endovascular revascularization consists of percutaneous dilation of the renal artery (often termed percutaneous transluminal angioplasty, or PTA). The femoral or radial artery is catheterized using the classic or modified Seldinger technique. Under fluoroscopic guidance, with occasional injections of contrast material to opacify the vasculature, a flexible guidewire is advanced across the stenotic segment of the renal artery. A balloon catheter is then selected that is approximately equal to the diameter of the nonstenotic portion of the renal artery. The balloon is placed over the wire to the level of the lesion and then inflated to a high pressure. In patients with atherosclerosis, the inflated balloon fractures the plaque, whereas in patients with FMD, the balloon stretches the vessel wall. In either case, perfusion to the kidney is markedly improved. A postdilation angiogram is performed to assess the results and determine the presence of any complications, such as injury to the vessel wall. An adjunct to PTA is the deployment of an endovascular stent, which is an expandable, metallic mesh sheath that helps maintain vessel patency. Stents are especially useful in the treatment of atherosclerotic stenoses, which tend to be rigid and may recoil after balloon dilation.

Surgical revascularization consists of bypass of the stenotic lesion or, less commonly, removal of the obstructing plaque (endarterectomy). Aortorenal bypass is often performed with an autologous graft, such as the saphenous vein. If an autologous graft is not available, a synthetic polytetrafluoroethylene (PTFE) or Dacron graft may be used instead. In patients with severe abdominal aortic disease, in whom aortorenal bypass would be challenging or even dangerous, alternatives include splenorenal or hepatorenal bypass. If both the abdominal aorta and celiac artery have severe stenosis, the lower thoracic aorta may sometimes be used instead. Simultaneous renal revascularization and replacement of the abdominal aorta should not be attempted unless there is another indication for aortic replacement, such as a large aneurysm.

Following either endovascular or surgical treatment, success is defined as elimination of the stenotic lesion on postprocedure angiogram or a postoperative blood pressure of less than 140/90. Many patients show improvements in blood pressure but do not become completely normotensive. The cure rate is greater among patients with FMD than among patients with atherosclerosis, in part because the latter group is more likely to have concomitant essential hypertension.

 

SURGICAL THERAPIES FOR RENAL ARTERY STENOSIS
Plate 10-18
SURGICAL THERAPIES FOR RENAL ARTERY STENOSIS

COMPLICATIONS

After endovascular repair, patients may experience acute tubular necrosis resulting from the contrast administered during the procedure. To reduce the probability of this complication, patients should receive adequate hydration both before and after the procedure. In addition, all other potentially nephrotoxic medications should be held. Other complications of endovascular repair include hematoma formation near the puncture site, thrombosis of the renal artery secondary to balloon trauma or to inadequate anticoagulation following stent deployment, and restenosis of the repaired lesion. The most serious complication is perforation of the renal artery, which is typically noted during the procedure. In this case, the balloon should be reinflated to tamponade the artery. Emergency open repair may be necessary if bleeding is persistent.

After surgical revascularization, complications include persistent stenosis, graft thrombosis, and restenosis of the repaired lesion. Mortality rates are very low among patients with FMD, owing to their young age and generally good health, but range from 2% to 6% among patients with atherosclerosis.

Patients who have recurrent stenosis after endovascular repair often require surgical revascularization. The surgical approach may be more challenging because of perivascular inflammation associated with the initial endovascular procedure; however, this difference does not appear to lower the probability of a successful outcome. Patients with recurrent stenosis after an initial surgical revascularization may undergo another surgical procedure with an alternative bypass route.