■ Progressive renal artery stenosis (RAS) or occlusion may predispose to renovascular hypertension (RVH; most common form of secondary hypertension) and ischemic nephropathy.2 Aortic atherosclerosis at the ostia or proximal renal artery accounts for two-thirds of cases.3 Fibromuscular dysplasia (FMD) also causes progressive serial stenoses throughout the renal arteries and may also predispose to RVH. FMD occurs most commonly in younger female patients.4
■ Acute mesenteric ischemia (AMI) and chronic mesenteric ischemia (CMI) are life threatening but fortunately rare (1 in 1,000 and 1 in 100,000 hospital admissions, respectively) conditions.5,6 The infrequent nature of symptomatic mesenteric ischemia may be due to the rich collateral supply derived from the celiac, superior, and inferior mesenteric arteries. CMI most commonly develops following progressive atherosclerotic occlusion of two or more mesenteric arteries, with the superior mesenteric artery (SMA) being the most critical of the three. Arterial embolization, leading to acute occlusion of the celiac artery or SMA, more commonly is associated with AMI.6 In rare circumstances, in critically ill patients, impaired intestinal perfusion due to arterial vasospasm may occur in the absence of thromboembolic occlusion.
■ Extra- and intraparenchymal renal artery branch aneurysms occur with a reported autopsy incidence between 0.01% and 0.7% and may arise from various disease etiologies.7 Overall, the risk of acute clinical evolution (rupture or thrombosis) is low but may be increased during pregnancy, with high resultant maternal and fetal mortality. The risk of progression/rupture, as is the case in most visceral artery aneurysms, is presumed to decline significantly following menopause.
■ Aneurysms of the celiac artery, SMA, and their branches are also infrequent and associated with varying etiologic entities. Splenic artery aneurysms are the most common (60%), followed by aneurysms in the hepatic (20%), superior mesenteric, and celiac arteries, in that order.8,9 Syndromes such as polyarteritis nodosa or Kawasaki’s disease may be associated with aneurysms in various segments of the mesenteric arterial circulation. Guidelines for intervention vary, depending on aneurysm location, rate of enlargement, symptom status, and demographic considerations: age, gender, and menstruation status.
PATIENT HISTORY AND PHYSICAL FINDINGS
■ RVH, with or without concurrent evidence of ischemic nephropathy, is seen in less than 50% of individuals manifesting severe RAS.2,3 Hypertension in children, new onset hypertension in individuals younger than 30 or older than 55 years old, or accelerated hypertension should prompt suspicion for the presence of RAS. Older patients with RVH/RAS typically manifest other stigmata of systemic vascular disease, including coronary and cerebrovascular disease, in addition to peripheral vascular disease. In patients with severe bilateral RAS, renal failure may be exacerbated with recent initiation of an angiotensin-converting enzyme (ACE) inhibitor.10 Acute exacerbations of poorly controlled RVH may manifest with “hypertensive crisis,” flash pulmonary edema, or neurologic symptoms ranging from headache to seizure and stroke. Physical examination may reveal severe elevation of both systolic and diastolic blood pressures, abdominal bruits, and other manifestations of peripheral arterial occlusive disease.
■ Patients with CMI are typically elderly and have a prior history of symptomatic vascular disease. Like RAS/RVH patients, CMI rarely is present without other signs and symptoms of advanced vascular disease, including aortic and mesenteric branch arterial calcification on plain x-ray films of the abdomen. Symptoms produced by CMI are frequently nonspecific and intermittent, leading to delayed diagnosis and disease progression. Classical symptoms usually include postprandial dull/crampy midepigastric abdominal pain, progressive weight loss, and “food fear” with decreased caloric intake.11 Findings on physical examination are usually noncontributory, save those related to advanced peripheral vascular disease (e.g., absent pedal pulses); patients frequently are malnourished and cachectic. Abdominal auscultation frequently reveals hyperactive bowel sounds, and a bruit may sometimes be auscultated.
■ AMI presents more dramatically, with sudden onset of abdominal pain, often in patients suffering acute embolic occlusion of the SMA. Although pain may seem out of proportion to objective physical examination findings initially, progressive tenderness to palpation and ultimately peritoneal signs develop in parallel with diminishing bowel viability. Clinical status also rapidly deteriorates, with progressive metabolic acidosis, shock, and multisystem organ failure.6
■ Patients with renal artery aneurysms (RAAs) may provide a history of trauma, arterial dissection, syndromic vascular conditions, connective tissue disorders, or RAS. The majority of RAAs are asymptomatic at the time of diagnosis, identified as incidental findings on cross-sectional imaging studies ordered for unrelated indications. Specific associated historical and physical findings are rare but may include acute onset hypertension, abdominal distension, flank pain, hematuria, syncope, and shock. Occasionally, an abdominal pulsatile mass is present on physical examination.7 Although not always fatal, RAA rupture, particularly those in segmental branches, frequently predisposes to renal infarction and resultant decrease in glomerular filtration capacity.
■ Patients with aneurysms of the celiac and SMAs and derived branches may manifest with a history of arterial dissection, trauma, pancreatitis, or other local inflammatory processes or infections. One-third of patients may also have aneurysmal disease in other segments of their arterial anatomy.8 As is the case with RAAs, patients rarely present with symptoms other than rupture, which itself is also rare. Free rupture may result in hemoperitoneum, hematobilia, or life-threatening gastrointestinal hemorrhage. The risk of rupture is highest with hepatic (20% to 44% of mesenteric arterial aneurysm ruptures) and splenic artery aneurysms, the latter notoriously at risk during the third trimester of pregnancy.12,13 Presence of a splenic artery aneurysm recognized during pregnancy should prompt consideration of immediate repair, regardless of the status of the pregnancy.14
IMAGING AND OTHER DIAGNOSTIC STUDIES
■ Renal artery disease assessment usually begins with duplex ultrasonography, which has a reported sensitivity of 86% to 93%, specificity of 98%, and overall accuracy of 96%.15 Duplex criteria used to diagnose more than 60% RAS include an arterial peak systolic velocity of more than 180 to 200 cm per second, a ratio of renal artery to aortic peak systolic velocity of more than 3.5, or acceleration time between onset and peak of systole of more than 100 m per second. Kidney length and resistive indexes derived from parenchymal insonation may also provide important insight into the presence, nature, and severity of end-organ disease.
■ Similarly, duplex ultrasound provides a useful, noninvasive method of assessing for the presence of chronic mesenteric occlusive disease.16 In the celiac artery, peak systolic velocities of more than 200 cm per second provides a sensitivity and accuracy for detecting a greater than 70% stenosis of 87% and 82%, respectively. In the SMA, peak systolic velocities of more than 275 cm per second provides a sensitivity and accuracy for detecting a greater than 70% stenosis of 92% and 96%, respectively.
■ Computed tomography angiography (CTA) is the current gold standard for confirming the presence, severity, and extent of occlusive mesenteric vascular disease. CTA-derived images also provide insights into the potential underlying mechanism of occlusion, including FMD, associated dissection, evidence of inflammation/infection, or thromboembolic occlusion. Moreover, three-dimensional reconstructions generated from CTA datasets also provide valuable guidance for preprocedural planning. In emergent circumstances, such as those associated with suspected AMI, CTA usually represents the “go-to” diagnostic test.
■ For patients with contrast allergies or other contraindications to computed tomography (CT) scanning, magnetic resonance angiography (MRA) may provide a suitable alternative, particularly for initial diagnosis and screening purposes. Overall resolution of MRA is not equal to that of CTA and in some circumstances may not provide sufficient detail for the precise surgical or interventional planning.
SURGICAL MANAGEMENT
Patient Selection
■ Appropriate patient selection for endovascular intervention is paramount and dependent on therapeutic indication, anatomy, patient comorbidities, and acuity of the disease process. In the following text, we discuss considerations for patients with renal/mesenteric arterial occlusive disease, followed by considerations for patients with renal/mesenteric arterial aneurysmal disease.
■ For RAS, the indication for endovascular intervention is contingent on severity of stenosis, the presence and severity of presumed resulting hypertension, and extent of residual glomerular filtration capacity. For RAS, there is no accepted indication currently for “prophylactic” intervention. Endovascular intervention is considered only in patients with severe hypertension, who have failed medical management with at least three concurrent antihypertensive medications or have demonstrated progressive loss of renal function due to ischemic nephropathy in the setting of more than 60% RAS. The future role for endovascular intervention in treating RVH has been called into question by level I data demonstrating only modest reductions in blood pressure following renal artery stenting.17
■ Patients with critical stenosis or occlusion of at least two mesenteric arteries, in the setting of signs and symptoms consistent with CMI, are also potential candidates for endovascular management. Patients with atypical symptoms who may meet anatomic criteria for mesenteric occlusive disease often experience disappointing results following endovascular intervention.
■ Given the compromises inherent in management of AMI, often in the setting of uncertain bowel viability, hybrid open and endovascular approaches may represent the safest and most expeditious option. Particularly in regard to “acute-on-chronic” occlusion of the proximal SMA, with a patent distal segment preserved by collateral flow, surgical exposure at celiotomy enables distal SMA cannulation and sheath placement. Standard angiographic techniques are then employed to cross the occlusive proximal lesion in a retrograde fashion, with subsequent angioplasty and stenting performed to restore pulsatile antegrade flow.18 We have employed this technique reliably under a variety of challenging clinical conditions with consistently good results.
■ In patients with disease in multiple mesenteric arterial segments and symptoms concerning for mesenteric ischemia, SMA revascularization, either via endovascular or open surgical approaches, represents the most reliable and effective method for resolving critical mid- and distal gut ischemia. Decompressive laparotomy should always be considered as an essential adjunct in these circumstances, regardless of revascularization method used, to facilitate selective resection of nonviable bowel if needed and limit the noxious effects of abdominal compartment syndrome in these already compromised patients.
■ In comparison, the safety and use of primary inferior mesenteric artery (IMA) endovascular intervention remains controversial in patients with disease in multiple mesenteric arteries. Recent series report relatively frequent procedure-related complications and poor outcomes following attempted IMA intervention.19 These results may in part be due to the progressive nature of occlusive vascular disease in the most distal aortic segment at the level of the IMA and resulting difficulty in resolving significant ostial stenoses with even high-pressure angioplasty techniques.
■ The criteria for elective repair of asymptomatic RAAs is controversial. Recommendations vary for intervention based on aneurysm diameter, also taking into account the size of the parent artery, extent of mural calcification, and rate of enlargement, if available. Consensus exists regarding treatment for all aneurysms larger than 3 cm in diameter.20,21 Similarly, patients with intact but symptomatic true aneurysms, recent-onset false (pseudo-) aneurysms, and aneurysms resulting from associated FMD are also typically repaired promptly, given their presumed higher risk of rupture. RAAs in women of childbearing age with plans for future pregnancies are usually repaired, when recognized, at almost any size. Less agreement is present for RAAs larger than 2 cm but smaller than 3 cm in diameter, with treatment recommendations often customized based on individual circumstances.
■ There are no set size criteria for visceral artery aneurysm repair. Although larger aneurysms are thought to have an increased potential risk of rupture, small visceral artery aneurysms are also known to rupture and manifest with life-threatening hemorrhage. Therefore, most visceral aneurysms larger than 2 cm should be repaired when identified. This recommendation does not necessarily apply to poststenotic arterial dilations (not true aneurysms) and distal SMA aneurysms. The latter are generally best managed by embolization and/or resection of the dependent loops of adjacent small intestine. In most circumstances, ruptured visceral artery aneurysms are best managed by open or hybrid approaches, allowing for assessment of bowel or end-organ ischemia in conjunction with restoration of arterial flow.
Preoperative Planning
■ Prior to attempted repair or exclusion, aneurysm location and access issues should be precisely determined via cross-sectional imaging studies. Luminal plaque, thrombus burden, associated aneurysms, and preexisting dissections should also be noted. Finally, target vessel diameter should be determined at several intervals before, within, and after the lesion of interest to optimize coil, stent, and graft selection.
■ The preferred method of critical renal artery ostial lesion management is by balloon-expandable stent placement. In rare circumstance, angioplasty predilation may be required to advance the appropriate stent through the renal ostia and across the stenotic lesion. Renal artery stents range from 10 to 30 mm in length and 4 to 7 mm in diameter. Transfemoral approaches to the renal artery are generally preferred due to the shorter distance to target, smaller imaging fields, and abundant availability of purpose-specific instrumentation. However, cephalad angulation of the renal artery origins relative to the aorta, the presence of extensive infrarenal aortoiliofemoral arterial occlusive disease, or significant iliac artery tortuosity may favor consideration of the left brachial artery and descending thoracic aorta as the preferred route of access.
■ For the treatment of mid- to distal RAS in the setting of FMD, angioplasty alone is generally the preferred treatment modality. Either transfemoral or transbrachial approaches may be considered, depending on the considerations noted earlier. Care must be taken to minimize procedural trauma with precise determination of target artery diameter and selection of appropriately sized instruments (sheaths, balloons, and stents). Poor planning or ill-considered procedural technique may precipitate arterial dissection, thrombosis, and renal infarction.
■ Depending on the degree of lesional calcification, the extent of associated juxtaostial aortic occlusive disease, lesion length and associated target vessel tortuosity, balloon- or self-expanding stent grafts may be chosen for luminal reconstitution and may provide improved long-term patency in the proximal SMA.22 Cannulation of either the celiac or SMA may be achieved from both femoral and brachial approaches. However, in emergent or extenuating circumstances, left brachial access often proves more expeditious and effective. This is particularly true in the setting of high-grade ostial stenosis or occlusion, where brachial access and antegrade aortic sheath placement may provide improved guidewire, sheath, and crossing catheter pushability and trackability.
■ Successful wire cannulation of ostial SMA and celiac lesions may require “telescoping” techniques with different sheath and wire combinations (see in the following text). This is also true of attempts to deploy devices in the mid- and distal splenic artery, where a triaxial catheter and sheath combination extending into the target lesion is frequently most effective. Given the short and often tortuous nature of the celiac artery, stable sheath placement is challenging, often representing the most difficult aspect of the procedure.
■ Similar principles are used when treating aneurysms of renal and visceral arteries, including precise catheter positioning and stable sheath support. Aneurysm size, location, neck anatomy, and extent of tortuosity of feeding target vessels impact the strategy of repair. For example, for large retropancreatic splenic artery aneurysms, coil embolization of the aneurysm sac (preferably with large-end-first or nesting coils) prior to covered stent placement across the ostium of the aneurysm is necessary to ensure long-term procedural success. For precise embolization of shallow or wide-necked aneurysms, adjuncts such as distal balloon occlusion with deployment of detachable coils may be necessary. For more accessible aneurysms with a wide-based aneurysm neck, bare metal stenting may be performed across the ostium of the aneurysm first, followed by placement of coils through the open interstices of the stent to keep the coils localized to the area of interest. Branch artery aneurysms usually occur at bifurcation points and are accompanied by small, well-defined necks and are ideally suited for embolization with microcoils (0.018-in catheter compatible) delivered through a triaxial delivery system.
■ The preferred size/shape of embolization devices or covered stents may be either accurately estimated from a preprocedural CT arteriogram or determined at the time of angiographic imaging and sheath placement. Based on these measurements, coil and plug diameters may be oversized by 20% of the target vessel diameter. The length of coils selected is derived from the anticipated arterial lumen surface area that requires embolization. Similarly, the length of vascular plugs selected depends on the target artery to be embolized and the estimated luminal flow. For example, higher flow arteries, such as those proximal to arteriovenous fistulae, usually need more extensive coverage to ensure definitive occlusion. Both self-expanding and balloon-expandable stent grafts are available. The former are also typically oversized by 20%, and the latter are usually sized 1 mm greater than the target artery diameter. Attention should be given to the sheath selection to ensure adequate diameter and length. The device-specific instructions for use (IFU) should be consulted in all circumstances prior to use of occlusion devices, or more generally, any endovascular device with the potential risk for significant vascular injury.
■ Depending on their specific location, some visceral artery aneurysms may be embolized without specific end-organ ischemic injury. However, embolization of distal aneurysms, such as those located within the splenic hilum, may result in splenic infarction, further bleeding, or abscess formation. Therefore, splenectomy remains a viable alternative method of splenic artery aneurysm management for many patients. Appropriate vaccinations should be administered with sufficient lead time to allow for an appropriate immunization response prior to elective splenic artery embolization procedures or planned splenectomy.
Operating Room Setup
■ Procedures may be performed in an angiography suite, or in an operating room, equipped with a floating-point carbon fiber, radiolucent operating table; fluoroscopy platform; and monitor-viewing bank. However, for precise visceral artery interventions requiring steep oblique/lateral imaging and higher fluoroscopic kilovolt (kV), portable systems in the operating room setting may not provide sufficient image clarity and resolution. Under these circumstances, use of a fixed-imaging system, either in an angiography suite or hybrid operating room, will maximize the likelihood of success.
■ For the majority of elective renal and visceral artery interventions, conscious sedation with a combination of short-acting analgesic and sedative agents will provide adequate patient comfort, immobility, and optimal imaging parameters. Standard patient safety measures for conscious sedation, including supplemental oxygen, standard monitoring, and availability of resuscitation equipment should be employed in compliance with local hospital policy. However, general anesthesia is clearly indicated to facilitate treatment of AMI, urgent/emergent management of aneurysm rupture, and/or hemorrhage potentially requiring bowel resection or open conversion.
■ For the most part, all renal and visceral artery endovascular interventions can be performed with the patient in the supine position. The left arm may be positioned out at 90 degrees to allow for transbrachial interventions. If a transfemoral intervention is planned, the patient’s arms may be extended over the head to aid with image clarity; however, most patients can only tolerate this for certain time periods prior to fatigue. Placing the patient in a 30-degree rotation to the right, on bolsters placed behind the left flank, at the time of the procedure, will facilitate “true lateral” position to localize and cannulate the origin of the SMA without requiring the image intensifier and radiation source to be in full horizontal position and limiting operator access to the patient as a result.
■ In addition to a full array of complementary wires, catheters, and sheaths, premounted balloon-expandable stents and stent grafts should be available, including in low-profile platforms (0.014 in or 0.018 in). Appropriate sizes of coils and plugs should also be identified and readily available.
