Renovascular disorders comprise several conditions that affect the renal arterial circulation. The majority of these conditions result in stenoses of the renal artery due to heterogeneous causes including atherosclerosis, fibrous dysplasia, vasculitis, neurofibromatosis, congenital bands, intrinsic occlusion from endovascular devices, and extrinsic compression from neoplasia and radiation. Nearly a century ago, renal artery stenosis was shown to cause severe hypertension from activation of the renin–angiotensin–aldosterone system. More recently, renal parenchymal loss and functional decline have also been determined as sequelae of renal artery disease and revascularization can lead to improvements in both blood pressure control and renal function.
The development of endovascular techniques for managing renal artery disease has had a profound impact on the role of open surgical procedures. Analysis of procedures done in 2009 shows that percutaneous techniques are utilized >30 times that of open renal artery reconstruction and >20 times that of combined renal and aortic reconstruction ( ). At present, open surgical approaches for renovascular disease remain the best option for patients with failed endovascular procedures, branch renal artery disease, and renal artery aneurysms. Notwithstanding their relatively higher morbidity, open procedures continue to provide for excellent long-term results.
General Vascular Surgical Principles
Proper instruments and fine suture needles are integral to the performance of successful vascular reconstruction. Instrumentation for vascular surgical procedures should include noncrushing vascular clamps, fine-tipped forceps, and needle holders for atraumatic grasp of blood vessel walls and suture needles, and an assortment of vessel loops and umbilical tapes for atraumatic vessel manipulation.
In order to minimize bleeding through needle holes, the caliber of suture for vascular repairs should be as fine as possible, without risking suture line disruption. Suture sizes ranging between No. 2-0 and 7-0 will most often be applicable for vascular procedures in the abdomen and pelvis. Nonabsorbable suture material should be selected for vascular repairs. Commonly used at present are nonabsorbable synthetic monofilament sutures, such as polypropylene, as these sutures are relatively inert in tissue; have a low coefficient of friction, thereby resulting in less tissue drag; and tend to retain a greater amount of tensile strength over time. In select instances, specifically that of pediatric vascular surgery, absorbable monofilament suture with a long half-life (e.g., polydioxanone suture) can be used to allow anastomotic growth.
In planned vascular operations, exposure and control of blood vessels is the first order of business. Knowledge of the vascular anatomy and characteristic appearance of the correct dissection plane greatly facilitate proper vascular exposure. While handling arteries, one should grasp only the periadventitial tissues with forceps rather than compressing part or all of the lumen as this may result in intimal disruption with dissection or distal embolization of loose atheromatous plaques.
In contrast to planned vascular operations, urologic procedures during which vascular complications occur require exposure of blood vessels in urgent or emergent situations. The most important tenet in managing unforeseen bleeding is that properly applied digital pressure can control virtually all abdominal and pelvic bleeding. Multiple attempts to use instruments, such as vascular clamps and hemostats, in a poorly exposed operative field carry significant risks of causing additional vascular injury and worsening the ongoing hemorrhage. With hemostasis obtained through digital pressure, the operative exposure should be improved with the goal of obtaining proximal and distal vascular control. Once this is accomplished, vascular clamps should be placed and digital pressure slowly released, allowing inspection of bleeding vessel. If hemostasis is unsatisfactory, these steps should be repeated until the site of injury can be fully examined. Attempts at suturing through poorly exposed tissues pose the risk of inadvertent injury to adjacent structures.
Two basic principles to consider when conducting vascular repairs are hemostasis and luminal patency so as to maintain flow. When restoration of flow is not required, as is the case in the pelvis where there is a rich collateral circulation, vessels can be ligated with ties or clips. When restoration of flow is intended, the vessel should be repaired such that ≥50% of the original luminal diameter is maintained. Reductions greater than this degree are likely to result in flow disturbances with hemodynamically significant consequences. In general, a transverse closure (perpendicular to the direction of blood flow) preserves the luminal diameter more than longitudinal closures. For arterial lacerations that cannot be closed in a primary manner, maintenance of luminal patency may require closure with an autogenous (usually venous) or synthetic vascular patch.
In the setting of vascular disruption or significant luminal compromise by a ligature or a clamp, excision and reanastomosis of the vessel may be required. As with other anastomoses, the fundamental principle of constructing a relaxed, tension-free anastomosis should be followed. When the ends of the vessel can be reapproximated in this manner, a simple end-to-end anastomosis can be constructed using either interrupted or continuous suture. In situations in which the two vessel ends cannot be reapproximated in a tension-free manner, an interposition graft of autogenous or synthetic material must be used.
Surgery for Renal Vascular Disease
Renovascular diseases refer to a variety of conditions that affect the renal arterial circulation, and much less commonly, the renal venous system. The majority of these conditions comprise stenoses of the renal artery from atherosclerosis, fibrous dysplasia, vasculitides, neurofibromatosis, extrinsic compression from neoplasia and intrinsic occlusion from endovascular devices. The pathophysiologic effects of renal artery stenosis are renovascular hypertension via activation of the renin–angiotensin–aldosterone system. In addition, hypoperfusion of the renal parenchyma may also result in declining renal function or ischemic nephropathy. These 2 conditions may present independently or together in the same patient and encompass the primary indications for intervention. Other less common renovascular diseases include renal artery aneurysms, arteriovenous malformations, and renal venous occlusion (Nutcracker syndrome).
Improvements in imaging and endovascular devices over the last few decades have led to a significant increase in the management of renal artery stenosis through an endovascular approach (percutaneous transluminal angioplasty and intraarterial stent placement). As a result, open surgical revascularization procedures are infrequently performed and, in general, reserved for patients with branch renal artery disease, renal artery aneurysms, or in cases of failed or complicated endovascular procedures. Recent studies, however, bring into question the benefit of stent placement over medical management. The recently published randomized prospective Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL) trial in patients with hypertension and atherosclerotic renal artery stenosis found no benefit to the addition of renal artery stenting to standard medical therapy alone ( ). Studies such as these may lead to an overall decrease in endovascular procedures and an increase in the proportion of open surgical approaches.
Surgical Indications
Renovascular Hypertension
Seminal experiments by Goldblatt and colleagues in 1934 identified the relationship between impaired renal perfusion and renovascular hypertension. Renal artery stenosis (RAS) resulting in ischemia causes the release of renin from the juxtaglomerular apparatus cells. Hyperreninemia promotes the conversion of angiotensin I to angiotensin II, which in turn leads to vasoconstriction, which causes hypertension. Furthermore, angiotensin II stimulates aldosterone release from the adrenals, which results in sodium and fluid retention, further perpetuating the hypertension.
The typical clinical picture in patients with angiotensin-mediated renovascular hypertension includes onset of hypertension at extremes of age (<30 or >55 years), accelerated or severe hypertension and hypertension refractory to optimal medical therapy. Physical examination findings suggestive of renovascular hypertension include retinal hemorrhage or retinopathy and systemic signs of fluid overload such as pulmonary and lower-extremity edema. Deterioration in renal function following treatment with angiotensin-converting enzyme (ACE) inhibitors is another indication of underlying renal artery stenosis.
Patients suspected of having renovascular hypertension should first undergo noninvasive imaging with duplex ultrasonography. This radiographic modality provides anatomic information regarding the kidney (size, parenchymal thickness, echogenicity), allows for characterization of renal blood flow within the main, segmental, and intraparenchymal renal arteries. Computed tomography (CT) and magnetic resonance imaging (MRI) angiography provide excellent anatomic detail and have sensitivities and specificities higher than 90%; however, the lack of blood flow information and renal functional consequences can only be indirectly inferred from findings of parenchymal atrophy. Furthermore, the use of intravenous iodinated contrast or gadolinium may be limited by the patient’s renal function.
Renal angiography remains the gold standard for confirming the diagnosis of renovascular hypertension with digital subtraction methods improving its resolution and decreasing the necessary amount of intravenous contrast. The diagnosis of renal artery stenosis is suspected when there is significant (>50%) narrowing of the renal artery lumen. As pressure differences across a luminal narrowing is exponentially related to diameter reduction, marked changes in pressure do not occur until the diameter reaches a critical threshold (~70% of original diameter). Beyond this critical level, RAS becomes hemodynamically significant, as evidenced by a >10% drop in blood pressure across the stenosis ( , ).
Angiography is also utilized in the diagnosis of patients with fibrous dysplasias of the renal artery. These disorders, which most commonly affect the mid to distal renal artery, are nonatherosclerotic, noninflammatory vascular diseases that are classified according to the affected layer of the arterial wall, that is, intima, media, and adventitia. Fibrous dysplasia affecting the media can be further subdivided into medial fibroplasia, perimedial fibroplasia, and medial hyperplasia. Ninety percent of patients have medial fibroplasia, which rarely progress to renal dysfunction or complications and thus can be managed medically. Patients with hypertension refractory to medical management can often be successfully treated with percutaneous approaches. Patients with intimal and perimedial fibroplasia tend to have severe hypertension and can progress with dissection, thrombosis, and renal dysfunction. Intervention for revascularizing such lesions is usually recommended as an early treatment.
Ischemic Nephropathy
Ischemic nephropathy is the loss of renal parenchyma and declining renal function secondary to a reduction in renal perfusion from renal artery stenosis ( ). Although no radiographic studies confirm the diagnosis of ischemic nephropathy, the finding of kidney size disparity on ultrasound (US), CT, MRI or radionuclide studies concurrent with hypertension strongly suggest this condition. Atherosclerotic renal artery occlusive disease is most often the underlying cause of ischemic nephropathy and can progress and eventually lead to renal functional loss. Renal artery revascularization is recommended to improve and/or stabilize renal function. The typical clinical picture of patients with ischemic nephropathy is often similar to patients with renovascular hypertension as atherosclerosis tends to be a common denominator.
Preoperative Preparation
As mentioned previously, intraarterial angiography is the gold standard to determine the nature, location, and treatment options for renovascular diseases. Arteriography also allows for precise assessment of the abdominal aorta and iliac arteries, as well as the origins of the celiac and superior mesenteric arteries (on lateral views) which is required to determine the optimal donor artery for revascularization. Current CT angiography provides essentially the same information and has an added benefit of clearly delineating extent and severity of calcific vascular disease.
Preoperative assessment of extrarenal vascular disease is also essential to ensuring satisfactory postoperative outcomes. Patients with atherosclerotic renal artery disease often have coronary artery, cerebrovascular, and/or peripheral arterial disease. Assessment and correction of conditions in these vascular beds prior to renal artery surgery may be required to minimize postoperative morbidity.
Intraoperative
Renal revascularization is most commonly performed through an anterior transperitoneal approach. Patients are placed in the supine position with the arms abducted ≤90 o for access by the anesthesia team. Hair is removed from the chest, abdomen, pelvis, groins, and upper thighs. These areas are prepped, and access to the anterior thighs for saphenous vein harvest is preserved by covering the genitalia with a sterile drape.
The selection between a midline versus transverse incision is dependent on surgeon preference as well as the planned operation. A midline approach allows for easier access to infrarenal aorta and pelvic vessels, should these be needed as interposition grafts or as a site of autotransplantation; whereas a transverse upper abdominal incision may provide for easier exposure of the hepatic and splenic arteries. In selected cases splenorenal bypass can be performed through a modified left flank approach (either retroperitoneal or transperitoneal), which allows access to both splenic and left renal arteries. With this approach, exposure to the remainder of the abdominal vasculature is limited, with minimal options for the surgeon if the planned procedure cannot be completed.
The surgical approach in patients with renal vascular disease should follow standard vascular surgical principles. Once the viscera have been mobilized and a self-retaining retractor placed, the diseased vessel(s) should be exposed only after obtaining proximal and, if possible, distal control. Once these have been accomplished, consideration should be directed toward procurement of the bypass conduit (e.g., saphenous vein, hypogastric artery). Prior to dissecting the renal vessels, mannitol (12.5 g) is administered to promote diuresis and minimize ischemic injury. Additionally, prior to initiating vascular anastomoses, heparin (10–15 U/kg) is administered systemically. Notwithstanding the relatively short anastomosis times, heparin given in these doses typically does not need to be reversed with protamine sulfate. Following clamp control of vessels, the periadventitial tissue is removed from the site of anastomosis and the artery opened sharply. The lumen is liberally irrigated with a heparin saline mixture. We first complete the proximal anastomosis and ensure flow through the bypass conduit and only then interrupt flow to the kidney in order to complete the distal anastomosis. This maintains renal blood flow for as long as possible and minimizes ischemic insult.
Aortorenal Bypass
Direct bypass from the adjacent aorta to the renal artery, or aortorenal bypass, is a straightforward renal revascularization technique. The area of dissection is limited and involves exposure of the aorta from the level of the renal arteries to the inferior mesenteric artery. Both the luminal caliber and flow within the aorta in this location are suitable for placement of a bypass conduit. On occasion, the aorta in this location can be involved with atherosclerotic disease, precluding aortorenal bypass. In these circumstances, a relatively disease-free portion of the aorta should be selected for the proximal arterial anastomosis, or an extraanatomic bypass procedure should be performed.
Conduits for aortorenal bypass may be autologous or synthetic. Autologous arterial grafts, such as a free hypogastric artery graft, are able to better withstand arterial pressure without long-term deterioration. Limitations of the hypogastric artery include its relatively short length and frequent involvement with atherosclerotic disease. Saphenous vein grafts offer good results and have proven durability. These grafts, which are most commonly used, are easy to procure, and of sufficient length for all required procedures. Long-term changes such as myointimal hyperplasia leading to stenosis or aneurysmal dilatation of graft can occur. Because of these concerns, saphenous vein grafts should not be used in the pediatric patient population. If no autologous material is available, a synthetic graft of polytetrafluoroethylene or Dacron may be used.
For aortorenal bypass to the right kidney, exposure is obtained by medial mobilization of the right colon and duodenum. The liver is retracted superiorly. The inferior vena cava, with insertion of the left and right renal veins, as well as the adjacent aorta, are centered in the operative field. A self-retaining retractor is utilized to maintain this exposure. The anterior perinephric fat should be removed so that the kidney parenchyma can be visualized and potentially biopsied following revascularization.
The anterior and lateral surfaces of the aorta (caudal to the left renal vein) are dissected keeping in mind that the only major branches in this location are the renal arteries. Lateral retraction of the inferior vena cava and superior retraction of the left renal vein should be considered to facilitate aortic exposure. Dissection along the right side of the aorta in a cephalad direction leads to the origin of the right renal artery posterior to the left renal vein. The right renal artery can be further exposed posterior and lateral to the inferior vena cava by retracting the cava and the right renal vein. Lumbar veins can be ligated and divided as necessary so as to improve the exposure. The renal artery is dissected distally toward the kidney, with the branches dissected as required from preoperative angiography.
After exposing a suitable donor area of the aorta, attention is directed toward procurement of an appropriate bypass conduit. Because of the need for a longer graft, the saphenous vein is commonly used and its length should be more than the anticipated length, as it should not be trimmed to the final length until the distal anastomosis. Knowledge of direction of flow within the saphenous vein should be maintained by distinguishing the ends. We typically leave the proximal (inflow) end open and clip the distal end. We utilize a longitudinal incision in the anteromedial thigh and ligate any small tributaries to the saphenous vein. The proximal and distal ends of the saphenous vein are isolated, with the distal end near the saphenofemoral junction. The proximal end of the vein is clamped and simply divided, verifying valvular competence in preventing retrograde flow. The distal end is clipped and the cut end at the saphenofemoral junction secured with a suture ligature. The vein graft is gently dilated by intraluminal injection of heparinized saline, and areas of extravasation are secured. The graft is then maintained in a cold heparinized saline solution.
The proximal or graft-to-aorta anastomosis is performed first. Vascular control of the aorta around the selected donor site is accomplished by cross clamping or tangential clamping. If the aorta is cross-clamped, lumbar arteries may have troublesome retrograde bleeding and should be controlled as well. An elliptical aortotomy is made along the anterolateral aspect of the aorta to allow for a gentle curve over the vena cava without proximal kinking or angulation. The vein graft is spatulated for a short distance, and an end-to-side anastomosis is performed ( Fig. 18.1 ). We prefer a continuous suture line using No. 5-0 or 6-0 polypropylene. A purse string effect can be avoided by securing the final knot with minimal tension.
After the proximal anastomosis is complete, the vein graft is clamped with a bull-dog clamp, and the aortic clamps are released. Any bleeding from the anastomosis can be secured at this time. We then allow the entire vein graft to dilate by temporarily occluding at the distal most extent. The entire graft is inspected, any bleeding points are controlled, and over a period of a few minutes the graft is suitably dilated throughout its length. Heparinized saline is injected retrograde and the bypass graft is reclamped approximately 1 cm beyond the proximal anastomosis. The renal artery (previously mobilized) is ligated proximally and clamped distally with a bull-dog clamp after injecting heparinized saline into the kidney. The diseased segment of renal artery is excised, and the vein graft can be trimmed at this time. Trimming should be done to allow enough length for a tension-free anastomosis without any redundancy that may predispose to kinking and thrombosis.
The distal anastomosis is then performed in an end-to-end fashion, typically with a slightly smaller caliber (No. 6-0 or 7-0) polypropylene suture. We typically use a continuous suturing technique; however, if the anastomotic lumen is small and difficult to visualize, an interrupted suture technique enables maximal visualization. The distal and proximal clamps are removed, and blood flow to the kidney is restored.
For left-sided aortorenal bypass, the left colon and the splenic flexure are mobilized to expose the renal hilum and the aorta. The renal artery is identified on the lateral aspect of the aorta. The donor site is chosen on the lateral aspect of the aorta on the left side, instead of anterolaterally on the right. The shorter graft distance on the left side makes the hypogastric artery more useful.
Patients with multiple renal arteries or disease involving renal artery segmental branches outside the renal hilum can be revascularized with a branched graft in situ ( Fig. 18.2 ). An in situ approach for branch disease is likely more complex than ex vivo repair but avoids a longer ischemic period, additional dissection, and renal vein anastomosis. The saphenous vein is particularly suitable for branched grafts, as it has enough length and can be fashioned into the desired configuration before anastomosis to the aorta or the renal artery branches. The hypogastric artery can be procured with its branches and used on the left side, but its use is limited by its fixed configuration, which might not fit the required branch configuration of the renal artery. As described previously, the proximal aorta-graft anastomosis is performed in the usual manner, but the distal anastomoses to the renal artery branches is different. Such branch anastomoses are usually delicate, and finer suture (No. 7-0) is required. Ligation of the renal artery branches and individual anastomoses are performed sequentially, which limits the overall renal ischemia time.
Extraanatomic Bypass Techniques
Extraanatomic bypass to the renal artery refers to procedures in which the inflow source arises from the hepatic, splenic, or iliac circulation. These procedures were generally performed in older patients with aortic atherosclerosis, aortic aneurysm, or fibrosis from previous surgery. More commonly done 2 to 3 decades ago when the morbidity from combined aortic replacement and renal revascularization was high, presently isolated extraanatomic open renal artery bypass from the hepatic or splenic arteries are rarely performed. As marked improvements in endovascular techniques have occurred, these approaches have markedly improved the morbidity and success rates of combined aortic and renal artery revascularization and are the primary therapeutic approach to patients with atherosclerotic disease of the aorta and renal arteries. For renal artery stenosis not amenable to endovascular management, iliac to renal artery bypass with saphenous vein or prosthetic grafts are commonly employed. From a technical standpoint, surgeons contemplating extraanatomic renal artery bypass should always assess the patency of the origin of the visceral arteries by viewing lateral projections of the aorta with the celiac and superior mesenteric artery origins. A similar assessment of these vessels can be made on current multiplanar computed tomographic angiography.
Splenorenal Bypass
Splenic to renal artery bypass is a suitable procedure for patients with a difficult aorta who need left renal revascularization ( Fig. 18.3 ). The advantages of this approach include avoidance of a diseased aorta, absence of an additional vascular conduit, a single arterial anastomosis, and proximity of arteries (splenic and renal) with similar caliber. Although tunneling of the splenic artery posterior to the duodenum for a right-sided splenorenal bypass has been described, the procedure is not considered to be suitable for right renal revascularization. Of particular note, visceral arteries, such as the splenic and hepatic, lack the same muscular layer as peripheral arteries; accordingly, these vessels must be very gently handled to avoid troublesome spasm or tearing during anastomosis.
