Renal artery aneurysm

INTRODUCTION — True renal artery aneurysms (RAAs) are rare. A true RAA is defined as a dilated segment of renal artery, the diameter of which exceeds 1.5 times the diameter of a normal segment and that involves all the layers of the arterial wall. A renal artery pseudoaneurysm does not involve all the layers of the arterial wall and is typically related to some form of traumatic injury, including iatrogenic injury (eg, renal biopsy) or arterial dissection [1].

A diagnosis of true RAA is commonly made incidentally with cross-sectional imaging obtained to evaluate unrelated pathology. Indications for repair of RAA continue to evolve with a trend toward more conservative management of asymptomatic small RAA, provided the risk for rupture is not elevated (eg, female with childbearing potential or who is pregnant) [2]. While open surgical repair of RAA still predominates, endovascular strategies for RAA repair have been increasingly reported.

The clinical presentation, diagnosis, and treatment focused on true RAA are reviewed. The diagnosis and management of other visceral artery aneurysms are presented separately. (See "Overview of visceral artery aneurysm and pseudoaneurysm" and "Treatment of visceral artery aneurysm and pseudoaneurysm".)

The management of renal trauma is presented separately. (See "Management of blunt and penetrating renal trauma", section on 'Vascular injury' and "Management of blunt and penetrating renal trauma", section on 'Vascular complications'.)

EPIDEMIOLOGY AND RISK FACTORS — RAAs are rare. Although the absolute incidence is unknown for certain, RAAs are estimated to occur in approximately 0.1 percent of the population.

Autopsy series have estimated an incidence ranging between 0.01 and 0.09 percent, but this likely underestimates the true incidence, since the more distal renal arteries (including intraparenchymal vessels) were frequently not scrutinized [3]. By contrast, the incidence of RAA is probably overestimated in angiographic and computed tomography studies (0.3 to 2.5 percent), which introduce a selection bias [4,5].

Females are more commonly affected compared with males, likely due to the higher incidence of associated fibromuscular dysplasia (FMD). RAAs are associated with FMD in up to 60 percent of females [6].

Risk of rupture — While reported rates of RAA rupture were high in historical series, this was likely related to the tendency for RAA to be identified only once symptoms had developed. In contemporary reviews, the overall risk of RAA rupture appears to be low [4,7-13]. In one large series, only 3/252 (1.2 percent) RAAs presented with rupture [9]. RAA rupture in those being conservatively managed is uncommon.

The risk of RAA rupture is increased with pregnancy, aneurysms associated with an inflammatory etiology (eg, polyarteritis nodosa, mycotic aneurysm), and larger aneurysm diameter (>3 cm) [14,15].

Pregnancy has long been associated with increased risk of RAA rupture, presumably due to hormonal changes that may disrupt blood vessel wall integrity, increased vascular volume and renal artery flow, and changes in abdominal pressure resulting from the mass effect of a gravid uterus [14,16-18]. Rupture associated with pregnancy has been reported to occur with smaller RAA diameter (≤3 cm) [18].

A review of the National Inpatient Sample (NIS) database from 2012 to 2018 identified 590 inpatient admissions for RAA associated with 554 procedures at 467 hospitals across the United States, of which 64.4 percent of these admissions were "nonelective" (ie, for rupture) [19]. Patients treated in the nonelective setting were less likely to have private insurance, more likely to be transferred, and had a higher "All Patients Refined Diagnosis Related Groups" (APD DRG) risk of mortality and severity of illness scores compared with those treated in the elective setting. While overall in-hospital mortality was similar for elective and nonelective settings (1.6 percent), patients treated in rural and nonteaching hospitals did have significantly higher in-hospital mortality rates (14.3 and 5.3 percent, respectively).

Associated conditions — Several conditions are associated with RAA and warrant further investigation when RAA is diagnosed. (See 'Further evaluation' below.)

In a single-institution review of 168 patients with 252 RAAs [9]:

●73 percent had documented hypertension

●34 percent had FMD

●25 percent had concomitant atherosclerosis (coronary heart disease, peripheral artery disease)

●6 percent had concomitant aneurysmal disease (eg, abdominal aortic aneurysm)

In a multi-institutional review that included 760 patients with 865 RAAs [10]:

●76 percent had difficult-to-control hypertension

●4 percent were associated with ipsilateral FMD

●10 percent had coronary artery disease

●Extrarenal aneurysm involved the abdominal aorta (37 patients), splenic artery (23 patients), thoracic aorta (13 patients), iliac artery (12 patients), celiac artery (5 patients), and hepatic artery (4 patients)

FMD causes abnormal arterial wall architecture that may lead to arterial aneurysm/dissection most commonly affecting the renal arteries, or extracranial carotid and vertebral arteries [20,21]. Patients with FMD with a history of smoking have an increased prevalence of aneurysm formation (in general, not specific to RAA), compared with those who have never smoked. (See "Clinical manifestations and diagnosis of fibromuscular dysplasia".)

Some, but not all, conditions associated with large vessel aneurysm formation have also been reported to be associated with RAA (eg, atherosclerotic degeneration, connective tissue disease, genetic conditions [Loeys-Dietz, Marfan syndrome (table 1), Moyamoya disease [22]], cystic medial degeneration, vasculitis [eg, Behcet disease]). (See "Epidemiology, risk factors, pathogenesis, and natural history of abdominal aortic aneurysm", section on 'Risk factors for the development of AAA' and "Epidemiology, risk factors, pathogenesis, and natural history of thoracic aortic aneurysm and dissection", section on 'Etiology and risk factors'.)

Other conditions associated with RAA include neurofibromatosis type I [23-25] and pseudoxanthoma elasticum [26].

Infected (mycotic) aneurysm can occur in the renal arteries and is associated with typical risk factors [27-29]. (See "Overview of infected (mycotic) arterial aneurysm", section on 'Risk factors' and "Overview of infected (mycotic) arterial aneurysm", section on 'Etiology'.)

RAA may be present in a donor kidney (related to any disease listed above), and these are typically repaired ex vivo prior to transplantation [30-32]. RAA subsequent to transplant has also been reported related to infection [33,34], but also arising de novo, sometimes many years after the transplant [35-37].

CLINICAL PRESENTATIONS — The clinical features of RAA are derived from case series [9,38,39]. RAA typically presents in the fifth to sixth decade of life, with females more commonly affected compared with males. In a review of 252 RAAs in 168 patients, the average age was 51 years, and the female-to-male ratio was 1.75 [9]. Most patients have no symptoms and may present with an incidental finding on imaging for an unrelated condition [10]. Some will be identified during evaluation for uncontrolled hypertension. Between 30 and 45 percent of patients are reported to develop symptoms [7,9,40]. When symptoms do occur, abdominal or flank pain or hematuria is most likely to be described [7].

Most patients with RAA lack traditional cardiovascular risk factors. However, more than one-third smoke cigarettes, and the majority are hypertensive. Depending on the series, up to 70 percent have fibromuscular dysplasia. (See 'Epidemiology and risk factors' above.)

Physical examination may reveal a renal bruit, or a palpable abdominal mass, but these findings are inconsistent and not specific for RAA.

Incidental finding — Most patients have no symptoms referable to the aneurysm. Most RAAs that are diagnosed incidentally are found on cross-sectional imaging obtained to evaluate an unrelated problem (eg, elevated liver function tests, preoperative evaluation) [9,41]. In one large series, 55 percent of patients presented incidentally [9].

Hypertension — RAA may also present during the course of evaluation for suspected renovascular hypertension (table 2). The relationship between RAA and hypertension is not well defined. Whereas only a small minority of patients who have hypertension will be diagnosed as having RAA due to its rarity, one- to two-thirds of patients with RAA are hypertensive [9-11,39,42-44]. Most patients with RAA and hypertension do not have concurrent renal artery occlusive disease (ie, renal artery stenosis) that would easily explain their hypertension, though the reported incidence of renal artery stenosis in patients with RAA has ranged widely from 3 to 66 percent [3,39,43].

Proposed mechanisms for decreased distal renal perfusion pressure and resultant hypertension, excluding renal artery stenosis in patients with RAA, include the following [42,45,46]:

●Distal parenchymal embolization (supported by the 8 to 11 percent incidence of thromboembolism)

●Compression or kinking of associated renal artery branches

●Hemodynamic changes from turbulent blood flow within the aneurysm

Regardless of the pathophysiology, hypertension tends to improve following RAA repair [10,43]. (See 'Postoperative care and follow-up' below.)

Pain associated with rupture — Most patients who rupture are not previously known to have RAA, and the diagnosis is made at the time of the rupture. Abdominal/flank pain and hypotension may represent rupture of RAA; however, such a presentation is nonspecific [15,47]. Whereas rupture of other visceral artery aneurysm (eg, hepatic artery aneurysm, mesenteric artery aneurysm) can rupture freely into the peritoneal cavity, most ruptures involving the RAA would be expected to be contained within the retroperitoneum.

Rupture and thrombosis of RAA can also lead to ischemic symptoms. (See "Renal infarction" and "Clinical presentation, evaluation, and treatment of renal atheroemboli".)

Rupture associated with pregnancy typically occurs during the third trimester and has been associated with even small aneurysm diameters (ie, 1 cm) [16-18]. Rupture has also been reported in the early postpartum period [14,48]. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients".)

Historically, high rates of maternal (56 to 92 percent) and fetal (82 to 100 percent) demise have been reported [18]. However, contemporary outcomes for mother and fetus appear to be improving [14,16].

Other symptoms

●Abdominal/flank pain not associated with rupture may be due to local changes in the arterial wall (eg, stretch from RAA expansion) or renal infarction from embolization. (See "Renal infarction" and "Clinical presentation, evaluation, and treatment of renal atheroemboli".)

●Painless hematuria is rare but has been reported to occur with RAA of any diameter. The mechanism is poorly understood but may be related to thromboembolism with renal infarction or renal vein compression by the RAA. (See "Etiology and evaluation of hematuria in adults".)

●Abdominal pain associated with systemic systems (eg, fever, fatigue) may be indicative of mycotic aneurysm. (See "Overview of infected (mycotic) arterial aneurysm".)

DIAGNOSIS — As with other peripheral arterial aneurysms, a diagnosis of RAA relies on the demonstration of the aneurysm either on vascular imaging studies or directly during abdominal exploration.

Vascular imaging — Computed tomographic (CT) angiography is the diagnostic study of choice to demonstrate RAA in hemodynamically stable patients. Given that ruptured RAA will generally be contained in the retroperitoneum, initial fluid resuscitation may allow imaging studies to be performed in patients who present with hypotension.

Compared with catheter-based arteriography or duplex ultrasound, CT angiography using multiplanar, maximal-intensity projection reconstruction; volume rendering; and three-dimensional reconstruction better assesses the details of renal arterial anatomy at all branch levels, including accessory arteries, or aberrant renal artery locations (eg, intrapelvic). CT angiography may provide a better representation of the number and relation of all involved branches; however, CT angiography may be limited in the definition of distal renal microaneurysmal disease and exposes the patient to ionizing radiation and iodinated intravenous contrast agents.

For those with radiation exposure risks such as children or women of childbearing potential, or those with contraindications to intravenous contrast material (eg, pregnancy, renal insufficiency, contrast allergy), noncontrast magnetic resonance (MR) angiography can be performed and is recommended for surveillance.

Imaging features — Most RAAs are single and unilateral with a right-sided predominance [9,49]. About 10 to 20 percent are bilateral [9,10]. In one large review, about one-third of patients had multiple RAAs [9]. RAA can affect any segment of the renal vasculature, including the main renal artery, accessory renal arteries [50], segmental arteries, or intraparenchymal arteries. Approximately two-thirds of RAAs involve an arterial bifurcation. Presumably, arteries supplying anomalous kidneys (eg, horseshoe kidney, pelvic kidney) can also be affected, but there are no data to suggest these pose an additional risk.

RAAs are more commonly saccular, rather than fusiform (about 80 versus 20 percent) (image 1) [9]. Between 20 and 56 percent have been reported as calcified [3]. There are no good data to support any correlation between any specific anatomic phenotype and the pathology or natural history of RAA.

The average diameter of RAA was 1.5 cm in one large review [9]. However, giant RAAs (5 to 12 cm) have been identified and treated, both ruptured and unruptured [51,52].

On imaging, patients with RAA may have associated RAAs, other visceral artery aneurysms (eg, splenic artery), or aneurysm at other locations (eg, cerebral, abdominal aortic aneurysm, iliac artery aneurysm) [4,9,53-55]. (See 'Concurrent aneurysm' below.)

Further evaluation — Additional evaluation may be warranted to further investigate hypertension or to identify associated conditions. Laboratory evaluation should include a basic hematology panel and chemistries, including baseline renal function studies and inflammatory markers.

Hypertension — For patients with hypertension, systemic renin values can be obtained. Ostial renal artery stenotic lesions may be identified with CT/MR angiography; however, catheter-based selective renal arteriography is necessary to assess for segmental/distal renal artery disease and arterial dysplasia/beading that may imply fibromuscular dysplasia (FMD). Intravascular ultrasound and manometry determine hemodynamic significance of any identified stenotic lesions. (See "Establishing the diagnosis of renovascular hypertension".)

Fibromuscular dysplasia — Patients with associated FMD should have a focused vascular review of symptoms. Given the association between FMD and RAA, we consider follow-up screening female patients with RAA for FMD with one-time CT or MR angiography for cerebrovascular, mesenteric, and iliac arterial FMD [21,56]. (See "Clinical manifestations and diagnosis of fibromuscular dysplasia", section on 'Clinical manifestations' and "Clinical manifestations and diagnosis of fibromuscular dysplasia", section on 'Choice of diagnostic imaging'.)

Concurrent aneurysm — Concurrent nonrenal arterial aneurysms are common, affecting up to one-third of patients [4,9]. All patients with RAA should have a one-time radiographic screening for asymptomatic aneurysm [21]. The most common sites include the carotid and intracranial arteries [53,54]. The visceral and vertebral arteries, aorta, and peripheral arteries are less frequently involved. (See "Clinical manifestations and diagnosis of fibromuscular dysplasia", section on 'Aneurysm and dissection'.)

DIFFERENTIAL DIAGNOSIS — Contrast-enhanced cross-sectional imaging is highly specific for a diagnosis of aneurysm, and the anatomy would typically be specific enough to localize the aneurysm to the renal artery vasculature. However, on noncontrast computed tomography, RAA could be mistaken for any "mass," including renal artery pseudoaneurysm, arteriovenous malformation, renal cyst, renal mass/tumor, or nephrolithiasis.

Renal artery pseudoaneurysm does not involve all layers of the arterial wall and may demonstrate perivascular inflammation, which distinguishes it from true RAA, although perivascular inflammation can be a feature associated with true mycotic aneurysm.

Prior isolated renal artery dissection, or extension of a dissection from the aorta, may also lead to renal artery pseudoaneurysm, and imaging would likely demonstrate additional imaging features related to dissection [21,54,57-59].

MANAGEMENT — Management of RAA depends upon whether symptoms are present, and for asymptomatic RAA, the risks associated with RAA repair compared with future RAA rupture. These risks are derived from observational studies that have reported on the natural history of untreated RAA [7,9,60,61] and outcomes of RAA repair (open surgery, endovascular repair). Our recommendations for management are generally consistent with the Society for Vascular Surgery guidelines for management of visceral artery aneurysms [2].

When to offer RAA repair — Patients who are symptomatic and those who are asymptomatic with an elevated risk for rupture (childbearing potential, RAA >3 cm) are offered repair; others with RAA are generally managed conservatively [2]. The suggested diameter threshold to offer repair in those with asymptomatic RAA is based on risk factors associated with rupture and natural history studies as described above. (See 'Risk of rupture' above.)

Repair ruptured and symptomatic, nonruptured RAA — RAA repair is required for patients with ruptured RAA as a potentially life-saving procedure [14-18].

For symptomatic RAA (any diameter), repair of RAA is indicated to manage complications, such as:

●Infected RAA (see "Overview of infected (mycotic) arterial aneurysm")

●Aneurysm expansion, arterial dissection, or renal infarction as the source of symptoms (eg, abdominal/flank pain, hematuria)

●Medically refractory hypertension associated with RAA (other causes of hypertension ruled out) [8-10,13,43,62,63]

Repair asymptomatic RAA with elevated rupture risk — For patients with an elevated risk for RAA rupture, the risks associated with rupture generally exceed the risks associated with repair, and repair is offered. These include females of childbearing potential, and those with RAA diameter >3 cm.

Females of childbearing potential — For asymptomatic RAA in females of childbearing potential who are not pregnant, repair can be considered regardless of diameter if the risk of the procedure is estimated to be less than the risk of rupture. As an example, for a small saccular aneurysm (1 cm) in a branch vessel, embolization can typically be accomplished with low risk of renal or systemic injury. On the other hand, a small renal aneurysm (<1 cm) involving multiple branches has a higher risk of renal parenchymal loss with either a complex embolization or open renal reconstruction and might warrant careful observation.

Rupture associated with pregnancy typically occurs during the third trimester and is associated with high maternal and infant mortality but has been reported to occur earlier in pregnancy [2,4,7-13,16,18,38]. Management of asymptomatic RAA in pregnant women is individualized, weighing the risk of rupture and potential morbidity to the mother and fetus with the morbidity associated with RAA repair.

The management other patient groups who may have an elevated risk for rupture (eg, immunosuppression, polyarteritis nodosa) is less well studied, and whether to offer RAA repair should be individualized. As an example, RAA associated with a donor kidney is often repaired prior to implantation [64].

RAA >3 cm — We agree with the Society for Vascular Surgery guidelines that suggest repair of RAA >3 cm in those with acceptable operative risk [2]. The historically accepted diameter threshold for intervening in patients with asymptomatic RAA has been 2 cm. While there remain no prospective studies or randomized trials that directly compare operative repair for RAA >3 cm with conservative management, the natural history of RAA appears to be more benign than previously assumed [65]. Like other visceral artery aneurysms, the natural history is indolent with slow to null growth. Series estimate a median annualized expansion rate of 0.06 to 0.6 mm with no differences related to aneurysm morphology or calcification [10-12,66]. In addition, during a period of conservative management, most authors report no ruptures, including successful surveillance of aneurysms >3 cm [9-12,39,66,67]. However, ruptures have been reported, more typically in the setting of multiple RAAs [68]. Reported rupture rates of RAA are overall low and estimated to be about 3 to 5 percent, which is much less than the high rates reported in historic reviews. In addition, reports of giant unruptured RAA (up to 12 cm) suggest that factors other than RAA diameter may be involved [51,52,69]. These data, combined with improved contemporary mortality rates when rupture does occur (<10 percent for nonpregnant patients [12]), support a more liberal diameter threshold than previously recommended.

Observe asymptomatic RAA with low rupture risk — Based on the generally benign natural history of RAA for males and for asymptomatic females without childbearing potential, we suggest conservative management for RAA ≤3 cm rather than repair because the risk of RAA repair exceeds the future rupture risk. Conservative management is also appropriate for patients with serious medical comorbidities who are not candidates for, or refused repair of, RAA [2].

Conservative management for RAA includes periodic evaluation of blood pressure and renal function and annual surveillance with renal duplex ultrasonography to evaluate for any changes in renal artery diameter [11]. For patients with elevated risk for rupture being managed conservatively, a more frequent interval may be warranted. If the diameter of the aneurysm has stabilized (no change in two years), the interval for surveillance can be prolonged to every two to three years.

Antiplatelet therapy has been suggested to minimize the potential for microembolization, given the well-described presence of mural thrombus within RAA [2,21]. We generally prescribe aspirin (81 mg daily) for patients who are not already taking antiplatelet medications for another indication (eg, secondary prevention of cardiovascular disease). For patients who are receiving other antiplatelet agents (eg, clopidogrel) or anticoagulants (eg, warfarin, direct oral anticoagulants), these should suffice.

Approach to repair

Preoperative arteriography — Catheter-based arteriography with magnified and oblique views is essential for preprocedural planning since it is better at identifying the RAA neck and relationship of all afferent and efferent branches of the RAA and, given its high spatial resolution, arteriography is more likely to identify distal microaneurysms. If the splenic or hepatic artery is being considered as inflow for a left- or right-sided extra-anatomic bypass procedure, respectively, it is important to ensure adequacy of the celiac artery radiographically.

If prior computed tomography/magnetic resonance angiography demonstrated a high likelihood that an endovascular approach would be appropriate, endovascular repair can be planned in the same setting following confirmation of the anatomy with diagnostic arteriography.

Elective repair: open versus endovascular — Repair of RAA can be more suited for one approach or the other depending on the anatomic features of the RAA, institutional resources, surgeon experience and preference, and patient preference. For most RAAs though, an open surgical approach remains favored over an endovascular approach for elective repair [2,38]. Surgical repair is durable as confirmed by long-term survival and low complication rates, especially for aneurysms involving the visceral hilum. Among published cases in a review that included 1279 RAA repairs, 72 percent were performed open, while 28 percent were performed using an endovascular approach [38].

Endovascular repair may be feasible in selected patients; however, late surgical conversion occurs in a significant number of patients due to incomplete aneurysm exclusion [70]. While RAA is increasingly being treated using endovascular techniques, these procedures appear to be in addition to, rather than replacement of, surgical repair. In retrospective reviews, the number of patients undergoing open repair has not decreased [71,72].

While there have been no prospective trials, institutional series and large database reviews comparing outcomes of open surgical versus endovascular RAA repair have found no significant difference in mortality between these approaches [2,38,71,72]. In a review of the National Inpatient Sample (NIS) database, which identified 1267 open RAA repairs and 1082 endovascular RAA repairs between 1988 and 2011, there was no significant difference in complication rates for open compared with endovascular repair (12.4 versus 10.5 percent), or for in-hospital mortality after risk adjustment [72]. Open repair was associated with significantly more cardiac complications (2.2 versus 0.6 percent), peripheral vascular complications (0.6 versus 0 percent), and longer length of stay (6 versus 4.6 days). In a later systematic review, which did not include the NIS data but included 358 endovascular RAA repairs from 28 case series and 921 open RAA repairs from 26 case series, there were no significant differences in short- or long-term mortality, need for reintervention, incidence of renal infarction, respiratory complications, or extended length of stay [38].

Ruptured aneurysm — Patients with abdominal pain and persistent hypotension with suspected aneurysm rupture are taken to the operating room to explore the retroperitoneal space and control hemorrhage. Once the ruptured vessel is identified and controlled and the patient has been resuscitated, the status of the contralateral kidney and any identified underlying connective tissue disorder will guide treatment strategies, which may include nephrectomy, repair and reconstruction of the renal artery, or angiographic embolization [16,73]. (See 'Open surgical reconstruction' below.)

In circumstances in which the patient with contained rupture responds to initial resuscitation and remains hemodynamically stable, an endovascular approach is preferred, particularly for high-risk surgical patients [74].

For pregnant women who present with rupture, a decision to sacrifice the kidney and management of the pregnancy (ie, monitoring, caesarian section, termination) is individualized [14,16,73]. As an example, women with a contained rupture responding to resuscitation and a fetus with no signs of distress may be successfully managed using endovascular techniques while carefully monitoring the pregnancy. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients" and "Nonobstetric surgery in pregnant patients: Patient counseling, surgical considerations, and obstetric management".)

Bilateral aneurysms — For patients with bilateral RAA, each RAA is treated independently based upon the patient's risk, diameter criteria, and any evidence for rapid expansion [28,68,75]. If right- and left-sided RAA both met criteria for repair, concurrent repair is appropriate if an open surgical approach is chosen, whereas if an endovascular approach is selected, staged management is chosen to limit radiation and iodinated contrast exposure.

OPEN SURGICAL RECONSTRUCTION — Open surgical reconstruction is generally favored for elective repair of most RAAs. (See 'Elective repair: open versus endovascular' above.)

Robotic-assisted laparoscopy techniques for RAA repair have been described in small case series with good technical success. This approach often relies on a multidisciplinary collaborative procedural team of vascular, general, transplantation, and urology surgeons [76-80].

Incision and exposure — An upper abdominal subcostal or transverse incision extending across the rectus musculature and onto the ipsilateral flank is preferred for distal renal exposure. (See "Incisions for open abdominal surgery", section on 'Subcostal'.)

A generous ipsilateral medial visceral rotation (right or left) facilitates exposure of the extraparenchymal renal vasculature, including the renal hilum, inferior vena cava, and the aorta.

●(See "Overview of the diagnosis and initial management of traumatic retroperitoneal injury", section on 'Right medial visceral rotation'.)

●(See "Overview of the diagnosis and initial management of traumatic retroperitoneal injury", section on 'Left medial visceral rotation'.)

Complete venous dissection and mobilization is required for exposure of the posteriorly located renal arteries. The dissection includes the inferior vena cava when the right RAA is being treated. For a saccular aneurysm originating at a bifurcation, it is imperative that all the renal artery branches are identified and isolated distal to the aneurysm prior to undertaking repair. Small microvascular clamps are used to control outflow branches in a way that leaves the operative field unencumbered.

Renal protection measures — To prevent thrombus formation and potential thromboembolism, the patient is systemically anticoagulated prior to clamping the vessels coming into and out of the RAA. The activated clotting time is maintained greater than 250 seconds for the duration of the repair. Once the repair is complete and adequate flow has been demonstrated by Doppler, we reverse anticoagulation to aid with hemostasis.

Osmotic diuresis is often established with mannitol (typical dose 25 g) prior to clamping.

All efforts are made to limit total warm renal ischemia time to <30 minutes. Staging renal branch anastomoses may aid with this and limit the total duration of warm renal ischemia. To reduce the risk of acute kidney injury, some authors advocate cooled (4°C) renal perfusion supplemented with mannitol or prostaglandin E when warm renal ischemia is expected to exceed 30 to 40 minutes [9,42,43].

Aneurysm repair — Few studies are available comparing surgical techniques for RAA repair. There are no prospective or randomized data, but a handful of small observational studies suggest minimal, if any, differences, underscoring that anatomy and location of RAA likely dictate the best technique to use. In one review, there was no difference in long-term event-free outcome for patients undergoing aneurysm resection and angioplasty compared with renal artery bypass [43].

Repair by location/anatomy — The patient's arterial anatomy and RAA location generally determine the specific surgical technique [39,49,81]. Specifically:

●Aneurysms of the main renal artery may be treated with excision and primary reanastomosis if adequate length can be mobilized; otherwise, an interposition bypass will be required. Large saccular aneurysms can often be resected, and the vessel repaired primarily. If there is concern for tension on the repair, separation of renal attachments to the abdominal wall and medial renopexy may help. (See 'Aneurysm resection and repair' below.)

●Aneurysms located at the primary branch point (typically of the distal main renal artery) can be longitudinally excised and the defect closed primarily either in a transverse fashion (Heineke-Mikulicz) or with a patch angioplasty. Following resection of aneurysms with several outflow vessels of variable caliber, the vessels can be separately reimplanted onto a bypass graft or spatulated and sutured together to provide a common outflow target for the graft. (See 'Aneurysm resection and repair' below.)

●Distal (segmental) aneurysms may be treated with excision or exclusion of the aneurysm, and distal renal artery bypass. Aortic inflow is favored over extra-anatomic bypass (eg, iliac, hepatic, splenic artery inflow). Alternatively, small distal aneurysms may be amenable to plication. (See 'Aneurysm exclusion and bypass' below and 'Aneurysm plication' below.)

●Some advocate for in vivo repair even for complex RAA or multiple RAAs [13,39,82]. (See 'Ex vivo repair and autotransplantation' below.)

●Unreconstructable disease implying disseminated, particularly distal, arterial dysplasia or a nonfunctional/atrophic kidney may require nephrectomy. Nephrectomy may also be needed for RAA rupture as a lifesaving measure if bleeding cannot be controlled. (See 'Nephrectomy' below.)

Surgical techniques — Surgical management of RAA may include aneurysm plication, aneurysm resection and arterial repair, aneurysm exclusion and bypass, ex vivo repair and auto-transplantation, or rarely nephrectomy. Multiple ipsilateral RAAs are not uncommon and are treated simultaneously, but they may require different technical approaches.

For treatment of a small segmental aneurysm branch concurrently treated with open repair of a larger, more proximal aneurysm, embolization of the resultant occluded segmental branch can be used to reduce the risk for future renovascular hypertension.

Aneurysm plication — Aneurysm plication (suture closure of redundant arterial wall) is an option for small aneurysms (<1 cm), typically in a setting concurrent with repair of a separate/larger aneurysm, and specifically for RAA due to post-stenotic dilation when the stenotic lesion has been addressed surgically. Plication has also been described in cases of nonatherosclerotic disease in children and young adults.

Aneurysm resection and repair — Depending on aneurysm morphology and location, the aneurysm can be partially or completely resected. Options for repair include primary angioplasty (with or without branch reimplantation), patch angioplasty, primary reanastomosis, or interposition grafting (figure 1 and figure 2 and figure 3).

Aneurysm exclusion and bypass — If the aneurysm is not amenable to excision and repair, then excision or exclusion of the aneurysm by ligation proximal and distal to the aneurysm and renal artery bypass are recommended (figure 4). When bypass is used, prosthetic conduit may be favored for large (>4 mm) distal targets; otherwise, autogenous conduit is preferred (ie, hypogastric artery for young patients or reversed great saphenous vein), although any vein conduit (eg, small saphenous vein, arm vein) can be used as necessary if the great saphenous vein is inadequate.

If aortorenal bypass is required, the infrarenal aorta is favored for inflow, and, if not suitable, alternatives include hepatorenal bypass for right RAA and splenorenal bypass for left RAA. The iliac artery can also serve as an inflow vessel.

Ex vivo repair and autotransplantation — Ex vivo repair and autotransplantation have been described in several series and case reports [39,83-89], offering reconstruction options for complex distal/branch lesions in lieu of nephrectomy, which was commonly performed in historic series. The involved kidney is exposed through a midline or extended flank incision. The proximal ureter is partially mobilized but left intact. The renal artery is divided proximal to the aneurysm, and the renal vein is divided proximally to include an ellipse of inferior vena cava to facilitate later reanastomosis. The kidney is brought ex vivo, typically placed on the abdominal wall, and chilled with topical saline slush and with direct renal artery perfusion using intermittent intra-arterial flushes. When cooling is completed (goal temperature 10 to 15°C), the aneurysm is opened and distal arterial revascularization is performed. The kidney is replaced into the renal fossa, and the renal vein is reattached to the inferior vena cava and the kidney is reperfused. A laparoscopic approach for nephrectomy followed by heterotopic kidney autotransplantation through the extraction incision is favored by some authors [90].

Nephrectomy — Under elective circumstances, unreconstructable disease implying disseminated, particularly distal, arterial dysplasia or a nonfunctional/atrophic kidney may require nephrectomy.

RAA rupture, whether preoperative or intraoperative, may necessitate nephrectomy if vascular control cannot be effectively secured. (See "Abdominal vascular injury", section on 'Renal arteries'.)

Post-repair intraoperative assessment — Following reconstruction and restoration of renal perfusion, adequate Doppler waveforms should be present throughout the arterial repair, outflow vessels, and renal parenchyma.

If the kidney is slow to reperfuse and pinken up following revascularization, or handheld Doppler interrogation yields inadequate signals, vasospasm or a technical issue may need to be remedied. Subadventitial injection of papaverine or nitroglycerin may be all that is necessary to address vasospasm, which is common in young adults. There should be a low threshold for revision if there is no improvement. Intraoperative duplex ultrasound can be used as an adjunct to guide revision. We do not routinely perform intraoperative renal arteriography to avoid the risk of contrast-induced nephrology in the face of warm ischemia.

ENDOVASCULAR TECHNIQUES — Conventional endovascular techniques may be considered for the elective repair of anatomically appropriate RAAs.

Stent-graft exclusion of main RAAs and embolization of distal and parenchymal aneurysms have been well described with good technical success.

Contemporary reports and small institutional series propose broadened indications for endovascular technology that include the use of three-dimensional detachable coils, nonadhesive liquid embolic agent, remodeling techniques that consider balloon- and stent-assisted coiling, and flow diverting stents [63,71,72,91-113]. Larger endovascular series note technical success rates of 73 to 100 percent, with highly variable morbidity (4 to 60 percent).

POSTOPERATIVE CARE AND FOLLOW-UP — Following open reconstruction, the patient is typically hospitalized from 5 to 10 days. Following endovascular repair, the duration of hospitalization is typically 24 to 48 hours to monitor blood pressure and renal function.

Staged completion arteriography — We obtain completion digital subtraction arteriography (DSA) (image 2) prior to discharge to fully assess the reconstruction. Arteriography is intentionally staged (ie, delayed for several days after the procedure), rather than immediately following repair/reconstruction to avoid the consequences of contrast-induced nephrotoxicity in the setting of renal ischemia/perfusion. For proximal renal artery reconstruction, CT angiography rather than DSA may provide adequate resolution; however, for first order and distal branches, spatial resolution with CT angiogram is limited. Another disadvantage for CT angiography is that more intravenous contrast is required compared with selective renal DSA. MR angiography is limited for postoperative renal assessment.

Most patients will already be receiving antiplatelet therapy (eg, aspirin) indefinitely to manage either atherosclerosis or a diagnosis of fibromuscular dysplasia (FMD). For those who are not taking already taking aspirin, we suggest aspirin for at least six months and have a low threshold for maintaining aspirin indefinitely following revascularization (eg, prosthetic graft) [114].

Resolution of hypertension — A significant number of but not all patients with RAA and hypertension have significant improvements in their blood pressure after RAA repair. Hypertension improves in 50 to 80 percent, particularly if renovascular hypertension was confirmed preoperatively [9,13,39,42,43]. In a review of 75 patients treated with RAA reconstruction, hypertension improved more often in those patients with documented renal artery stenosis compared with those without (67 versus 29 percent) [43]. In a review of patients treated for RAA predominantly due to FMD, hypertension was cured in 25 percent and improved in 39 percent [115].

Ongoing surveillance — Following RAA repair, routine follow-up is important. This includes periodic assessment of blood pressure and renal function, and renal duplex ultrasound. We follow up with renal duplex at one month and every six months for the first two years, and annually thereafter if there are not issues. In the first two years, the repair is at risk for developing neointimal hyperplasia.

Increasing hypertension, decline in renal function, or abnormal duplex findings should prompt further study with catheter-directed arteriogram.

We have a low threshold to obtain computed tomographic angiography for patients treated with embolization or stent-grafting to assess for postembolization recanalization or for endoleak.

MORBIDITY AND MORTALITY — The young age of many patients and excellent anticipated long-term survival (up to 91 percent at 10 years) reinforce the applicability of open surgical techniques for renal revascularization, which offer low morbidity, negligible mortality, and durable patency across series [2,38,71,72,116].

Complications — Following RAA repair (open or endovascular), complications occur in about 1 percent of patients [10,72]. Renal malperfusion from thromboembolism and resultant postembolization syndrome is the most common complication described. Other complications include arterial dissection, renal failure, and late recanalization, and are less common, affecting 4 to 13 percent of patients.

Prolonged warm renal ischemia may result in acute kidney injury requiring renal replacement therapy. At least three months should be allowed for renal recovery in this situation. Measures to limit warm renal ischemia and protect the kidney during repair are discussed above. (See 'Renal protection measures' above.)

Reintervention — Primary patency rates are 75 to 100 percent across series, and reintervention rates are very low. Balloon angioplasty for stenosis is more common for endovascular salvage than is remedial surgery or secondary nephrectomy.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Aortic and other peripheral aneurysms" and "Society guideline links: Fibromuscular dysplasia".)

SUMMARY AND RECOMMENDATIONS

●Renal artery aneurysm – True renal artery aneurysms (RAAs) are rare. A true RAA is defined as a segment of renal artery, the diameter of which exceeds 1.5 times the diameter of a normal segment and involves all the layers of the arterial wall. True RAAs can involve any portion of the renal arteries. Most RAAs are single, unilateral, and saccular with a right-sided predominance. (See 'Introduction' above.)

●Risk factors – Risk factors for RAA include female sex, likely related to the association of RAA with fibromuscular dysplasia (FMD). Most patients with RAA lack traditional cardiovascular risk factors, although more than one-third smoke cigarettes, and most have hypertension. (See 'Epidemiology and risk factors' above.)

●Clinical presentations – RAA typically presents in the fifth to sixth decades of life. Most patients are asymptomatic. When symptoms occur in a nonruptured RAA, abdominal or flank pain or painless hematuria is most likely to be described. Physical examination findings when they occur (eg, bruit, abdominal mass) are nonspecific. (See 'Clinical presentations' above.)

●Diagnosis – A diagnosis of RAA relies on the demonstration of the aneurysm either on vascular imaging studies or directly during abdominal exploration. Most RAAs are diagnosed incidentally on cross-sectional imaging obtained for other reasons. For patients suspected of having RAA, computed tomographic (CT) angiography is the diagnostic study of choice. Noncontrast magnetic resonance (MR) angiography can be used when radiation exposure or iodinated contrast agents are contraindicated. Additional evaluation may be warranted to further investigate hypertension or to identify associated conditions (eg, FMD, concurrent aneurysmal disease). (See 'Diagnosis' above and 'Further evaluation' above.)

●Management of symptomatic RAA – RAA repair is required for patients with ruptured RAA as a potentially life-saving procedure. Rupture is estimated to occur in about 3 to 5 percent of RAA. Most patients who rupture are not previously known to have RAA. Repair of symptomatic, nonruptured RAA is also indicated to manage complications of RAA. (See 'Risk of rupture' above and 'Repair ruptured and symptomatic, nonruptured RAA' above.)

●Asymptomatic RAA at risk for rupture – For asymptomatic RAA associated with elevated rupture risk, we generally offer repair. The risk of rupture is increased with pregnancy, aneurysms associated with an inflammatory etiology, and larger aneurysm diameter.

•For asymptomatic RAA in women of childbearing potential who are not pregnant, we suggest elective repair rather than conservative management (Grade 2C). Repair can be considered for any RAA diameter if the risk of the procedure is estimated to be less than the risk of rupture.

•For asymptomatic RAA during pregnancy, management is individualized, weighing the risk of rupture and potential morbidity to the mother and fetus with the morbidity associated with RAA repair.

●Asymptomatic RAA at low risk for rupture – For asymptomatic RAA in patients at low risk for rupture, we manage RAA conservatively with repair offered based primarily on RAA diameter, weighing the risk of repair with the overall low risk for future rupture. The optimal threshold diameter at which to offer elective repair in those being managed conservatively is uncertain and is largely based on observational data on the natural history of RAA and the risk of rupture.

•For asymptomatic RAA ≤3 cm in men and females without childbearing potential, we suggest conservative management, rather than repair (Grade 2C).

•Conservative management for RAA includes periodic evaluation of blood pressure and renal function and annual surveillance with renal duplex ultrasonography to evaluate for any changes in renal artery diameter. For patients with elevated risk for rupture being managed conservatively, a more frequent interval may be warranted.

●RAA repair – The patient's arterial anatomy and aneurysm location generally dictate the surgical approach and technique that are used. Open surgical reconstructive techniques, which may include plication, aneurysm resection and arterial repair, and aneurysm ligation and renal artery bypass, are favored by most vascular surgeons for elective repair of RAA. Rarely nephrectomy may be required for unreconstructable disease or to manage ruptured RAA. Morbidity and mortality associated with RAA repair is overall low, regardless of approach (eg, open or endovascular repair) or repair technique. End-organ malperfusion from thromboembolism is the most common complication associated with RAA repair. Following repair, primary patency rates are overall high (75 to 100 percent), and reintervention rates are very low. (See 'Approach to repair' above and 'Morbidity and mortality' above.)

●Follow-up after repair

•Following repair of RAA (elective or emergency), staged completion arteriography is obtained several days after the procedure but prior to discharge to assess the reconstruction. We suggest digital subtraction arteriography for most patients to minimize intravenous contrast administration, although for some proximal reconstructions, CT angiography may be adequate. (See 'Staged completion arteriography' above.)

•Subsequent follow-up includes regular assessment of blood pressure and renal function as well as renal duplex at one month and every six months for the first two years. Increasing hypertension, a decline in renal function, or abnormal duplex findings should prompt further study with catheter-directed arteriogram. (See 'Ongoing surveillance' above.)