Description

Carotid endarterectomy is performed through a neck incision along the medial aspect of the sternocleidomastoid muscle. The carotid bifurcation is the most common location of carotid occlusive disease, and control of the common, internal, and external carotid arteries must be obtained. An incision is made along the common carotid extending through the plaque to an area of nondiseased internal carotid artery. The plaque is then elevated from the adventitia along with the intima. Finally, the arteriotomy is closed with a synthetic or autologous patch, which decreases the risk of restenosis compared with primary closure.

Indications

Vascular surgeons are particularly stringent about the indications for carotid endarterectomy because this is one of the few prophylactic operations. Indications for carotid endarterectomy are based on two large, multicenter, randomized trials comparing best medical therapy (antiplatelet) and surgical therapy for carotid stenosis. The North American Symptomatic Carotid Endarterectomy Trial (NASCET) examined patients with a previous history of stroke, transient ischemic attack, or amaurosis fugax within 3 months of enrollment.¹ During 2 years, the risk of stroke in patients with a 70% to 99% stenosis was reduced from 26% to 9% with carotid endarterectomy. The risk of stroke in patients with a 50% to 69% stenosis was reduced from 22% to 16% during 5 years. Given the less substantial benefit seen with the moderate-grade lesions, most vascular surgeons would recommend carotid endarterectomy to symptomatic patients with 50% to 69% stenosis only if they have a substantial life expectancy and low risk of complications related to the surgical intervention. Finally, subgroup analysis revealed an increased risk of stroke in medically treated patients with contralateral carotid occlusions and ulcerated plaques.

The Asymptomatic Carotid Atherosclerosis Study (ACAS) randomized asymptomatic patients to medical and surgical therapy.² Carotid endarterectomy reduced the 5-year risk of stroke from 11% to 5% in patients with 60% to 99% stenosis compared with medical therapy. Given an absolute stroke risk reduction of 6% during 5 years, further studies have shown that surgical therapy is most beneficial in patients with 80% to 99% stenosis and in men compared with women. This equates to changing the outcome of approximately 1 in 20 to 30 patients, making the safety and risk reduction in the conduct of intervention for asymptomatic patients of paramount importance. This fact significantly affects the decision-making process regarding carotid imaging for either carotid endarterectomy or carotid stenting. In the ACAS trial, there was a 1.5% risk of stroke from diagnostic angiography alone.

Contraindications

Cardiopulmonary comorbidities preventing surgical intervention and total occlusion of the internal carotid artery are the only absolute contraindications to carotid endarterectomy. The risks related to cardiopulmonary comorbidity may be reduced by the use of local or regional anesthesia, thus limiting the systemic effects of general anesthesia. Carotid endarterectomy is not performed on patients with occlusion of the internal carotid artery as the thrombus typically extends to the ophthalmic artery. Relative contraindications to surgery are based on the exclusion criteria of the NASCET and ACAS trials, including, among others, patients with recent myocardial infarction (symptomatic coronary artery disease), uncontrolled diabetes mellitus, and advanced age. Anatomic risk factors include previous neck irradiation or dissection, tracheal stoma, carotid lesions at or above the second cervical vertebra, contralateral vocal cord paralysis, and previous carotid surgery.

Further studies examined carotid endarterectomy and found that it can be safely performed in patients deemed at high risk, including those 80 years or older and others with significant comorbid conditions, with combined stroke and mortality rates comparable to those found in the NASCET and ACAS studies. Contralateral occlusion was the only predictor for moderately increased perioperative risk of stroke and reduced long-term survival.³

Overall, outcomes are based on the surgeon’s experience, and decisions about intervention are largely based on the track record of the team performing the procedure.

Outcomes and Complications

Outcomes related to surgical therapy are discussed earlier. The majority of patients do well after carotid endarterectomy and are discharged home by the first postoperative day.

The major complications related to carotid endarterectomy include perioperative stroke, cranial nerve injuries, cardiopulmonary complications, and restenosis. Recurrent stenosis can be in the form of three types occurring at different time stages: (1) residual disease from an incomplete endarterectomy usually can be seen immediately on postoperative imaging; (2) intimal hyperplasia frequently occurs between 2 months and 2 years; and (3) recurrent atherosclerotic disease most often occurs beyond 2 years. Open surgical repair of recurrence in any of these forms carries a higher risk of intraoperative complications, including cranial nerve damage secondary to postoperative scar formation. For this reason, carotid stent angioplasty is frequently used to treat recurrent disease.

One rare complication is hyperperfusion syndrome, which is characterized by a severe, unilateral headache occurring 3 to 7 days after endarterectomy. This has been attributed to the sudden restoration of normal arterial pressures in a vascular bed that has not seen pulsatility and normal pressures for a long period, thus leading to atrophy of the arteriolar restrictive mechanisms and impaired ability of the cerebrovascular circulation to autoregulate after the reestablishment of cranial blood flow. MRI may show reversible vasogenic edema similar to that observed in the posterior leukoencephalopathy syndrome.⁴ Treatment includes control of the hypertension that is frequently associated with this phenomenon to prevent cerebral hemorrhage until cerebral autoregulation is reestablished, typically for a few days to 1 week.

Imaging Findings

Preoperative Assessment

Duplex ultrasonography is the most common technique used to assess patients suspected of having extracranial cerebrovascular disease. B-mode ultrasonography is used to define location of the stenotic lesion, and Doppler examination is used to measure velocities across the stenosis (Fig. 87-1). B-mode ultrasonography not only delineates the location of a stenosis but also describes the characteristics of the plaque itself. Plaque ulceration as well as plaque calcification or hemorrhage may be seen. B-mode ultrasonography can also evaluate plaque echogenicity and the presence of thrombus. Soft, friable plaques on ultrasound examination are typically less stable than echoic plaques are. Mobile thrombus on ultrasound examination has been associated with an increased risk of stroke.

FIGURE 87-1 Duplex ultrasound examination of a patient with left internal carotid artery stenosis. Note the gray-scale lesion on the B-mode image and elevated Doppler velocity measurements across the stenosis.

Velocity measurements across a stenosis are the most important aspect of the preoperative assessment for the vascular surgeon because these measurements are directly correlated with degree of stenosis. Strandness⁵ first reported a sensitivity of 99% and a specificity of 84% with duplex ultrasound criteria for the evaluation of carotid disease compared with conventional angiography (Table 87-1). More recently, it has been observed that diagnostic criteria must be altered in the setting of a contralateral severe stenosis or complete occlusion of the internal carotid artery because of a compensatory increase in carotid blood flow. By use of the criteria of AbuRahma,⁶ the accuracy of duplex ultrasound measurements can be increased to 96%. No matter which criteria are used, they must be validated by individual vascular laboratories as this technique may be operator and instrument dependent.

TABLE 87-1 Duplex Ultrasound Criteria for Diagnosis of Internal Carotid Artery Stenosis

Stenosis	Criteria
	Strandness	AbuRahma
Normal	PSV < 125 cm/sec	PSV < 125 cm/sec
	No SB	No SB
	Flow reversal in bulb
1%-15%	PSV < 125 cm/sec	PSV < 125 cm/sec
	No or minimal SB	Minimal SB
	Flow reversal in bulb absent
16%-49%	PSV > 125 cm/sec	PSV < 140 cm/sec
	Marked SB	EDV < 140 cm/sec
50%-79%	PSV > 125 cm/sec	PSV ≥ 140 cm/sec
	EDV < 140 cm/sec	EDV < 140 cm/sec
80%-99%	PSV < 125 cm/sec	PSV > 140 cm/sec
	EDV > 140 cm/sec	EDV < 140 cm/sec
Occlusion	No flow	No flow

EDV, end-diastolic velocity; PSV, peak systolic velocity; SB, spectral broadening.

Modified from Strandness DE Jr. Extracranial arterial disease. In Strandness DE Jr (ed). Duplex Scanning in Vascular Disorders, 2nd ed. New York, Raven Press, 1993, pp 113-158; and AbuRahma AF, Richmond BK, Robinson PA, et al. Effect of contralateral severe stenosis or carotid occlusion on duplex criteria of ipsilateral stenoses: comparative study of various duplex parameters. J Vasc Surg 1995; 22:751-761.

Many surgeons will rely on duplex ultrasonography alone in making the decision to perform a carotid endarterectomy. Additional imaging is required in any case in which anatomic factors preclude a complete assessment by ultrasound examination. These include extreme tortuosity, inability to see normal distal internal carotid, or any factor that does not allow complete characterization of the carotid bifurcation and confirmation of a normal distal extracranial internal carotid artery. Furthermore, additional testing should be performed in the presence of the so-called string sign. String sign may occur in two scenarios that are treated differently. In the first, there is slow flow through a high-grade stenosis with an underfilled but normal internal carotid artery. In this case, carotid endarterectomy is beneficial. In the second case, there is a long-segment high-grade stenosis extending into the distal internal carotid artery. These types of lesions are more difficult to treat surgically and are associated with a higher perioperative stroke rate. Combining duplex ultrasonography with either computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) increases the overall accuracy of determining degree of stenosis.

CTA has been used to delineate extracranial cerebrovascular and carotid arch anatomy and has the advantages of minimal discomfort for the patient, relatively low radiation doses, and demarcation of calcific plaques in both the carotid arteries and the aortic arch. Recent three-dimensional reconstructions provide the surgeon with a greater ability in preoperative planning (Fig. 87-2).

FIGURE 87-2 Postprocessed view of three-dimensional CTA shows a left carotid stenosis with calcification (white) and plaque (yellow).

MRA is another tool of the vascular surgeon and can be particularly useful in patients with an allergy to intravenous contrast material. Time-of-flight MRA has a tendency to overestimate the degree of stenosis because of local blood flow turbulence. Overestimation of time-of-flight MRA can be reconciled with the performance of gadolinium-enhanced three-dimensional MRA.⁷ Both techniques also demonstrate intracranial vessel anatomy along with patency of the communicating arteries.

Catheter angiography (Fig. 87-3), previously considered the gold standard for the assessment of extracranial cerebrovascular disease, has been used less frequently in uncomplicated patients because of the approximately 1.5% risk of stroke. Catheter angiography is now typically reserved for evaluation of patients in whom results from duplex ultrasonography and either CTA or MRA are discordant.

FIGURE 87-3 Digital subtraction angiography showing high-grade stenosis of the internal carotid artery (arrow).

Description

Carotid-subclavian bypass may be performed through a remote cervical incision just lateral to the sternocleidomastoid muscle. The jugular vein is reflected medially to expose the common carotid artery. The anterior scalene muscle is then divided to expose the subclavian artery. Once proximal and distal control of each artery is obtained, bypass is typically performed with a prosthetic graft as patency is superior to autogenous conduit in this position.⁸ On occasion, concomitant disease of the ipsilateral common carotid artery precludes its use as an inflow vessel. In these cases, the contralateral common carotid may be used. The prosthetic graft would then be tunneled across the midline through the retropharyngeal space; this is a more direct path and avoids erosion of the overlying skin or interference with possible subsequent sternotomy or tracheostomy.

Indications

Indications for repair of subclavian stenosis include upper extremity disabling claudication, rest pain, and tissue loss. Patients with subclavian steal syndrome are also candidates for repair. Subclavian steal occurs when there is a stenosis of the first portion of the subclavian artery causing distal pressure to drop below that at the vertebrobasilar junction, with subsequent reversal of flow through the basilar and ipsilateral vertebral arteries. This can lead to vertebrobasilar symptoms of presyncope, syncope, or drop attacks. Finally, carotid-subclavian bypass should be performed in those patients with asymptomatic proximal subclavian stenotic lesions who are undergoing coronary revascularization through the internal mammary artery, as well as in patients with symptomatic coronary steal syndrome from a patent internal mammary artery coronary bypass graft.

Contraindications

Severe cardiopulmonary comorbidity is the only absolute contraindication to carotid-subclavian bypass. As described before, this procedure may be performed through a small incision, and local regional anesthesia may have fewer cardiovascular effects than standard general anesthetic techniques.

Outcomes and Complications

Outcomes from carotid-subclavian bypass are excellent, with 10-year patency rates of 84%.⁹ Complications range from a 0% to 1% stroke rate to a 0% mortality rate.^10,11

Imaging Findings

Preoperative Assessment

Duplex ultrasonography may be used to screen for subclavian stenosis but is limited by the bony structures of the mediastinum. Its usefulness lies in its ability to assess for reversal of blood flow in the vertebral artery with upper extremity exercise (Fig. 87-4) and the adequacy of the common carotid artery for inflow.

FIGURE 87-4 Duplex ultrasonography of common carotid and vertebral arteries showing reversal of flow within vertebral artery in a patient with subclavian steal syndrome. Note the opposite color of the vertebral artery (blue) compared with the common carotid artery (red).

CTA and MRA are useful tools to assess for lesions of the proximal subclavian artery. As a screening tool, CTA may be more practical because the examination is more widely available and generally quicker to perform.

In cases in which the diagnosis is questionable, digital subtraction angiography may be helpful to demonstrate reversal of flow through the vertebral artery.

Preoperative Planning

Once a subclavian stenosis has been identified, preoperative planning may be accomplished with CTA or MRA (Fig. 87-5). Both evaluate the exact location of the lesion as well as assess possible inflow and outflow vessels. Full appraisal of the aortic arch, its branches, and neck extracranial cerebrovascular vessels is necessary to rule out other pathologic processes. Resolution of the aortic arch and these large-caliber vessels with CTA and MRA is excellent, and they may replace standard angiography.

FIGURE 87-5 Coronal reformat (A) and axial (B) images from CTA show occlusion of the proximal left subclavian artery (arrows) in a patient with subclavian steal syndrome.

Digital subtraction angiography may be a useful adjunct for preoperative planning before carotid subclavian bypass. Angiography can identify major inflow and outflow vessels as well as important collaterals (Fig. 87-6).

FIGURE 87-6 Digital subtraction angiography showing occlusion of the proximal left subclavian artery (arrow) with reconstitution of left vertebral and distal left subclavian arteries. Real-time angiography showed retrograde filling of left vertebral artery.

In cases in which it is necessary to use the contralateral common carotid artery as inflow, CT scanning should be performed to evaluate the retropharyngeal soft tissues.

Description

Thoracoabdominal aortic aneurysm (TAAA) repair is performed through a retroperitoneal approach combined with thoracotomy. Intraoperative management of patients with thoracoabdominal aneurysms is dependent on the extent of the aneurysmal degeneration of the aorta. Patients with Crawford extent I and II TAAAs generally require either continuous distal perfusion or left-sided heart bypass; these types of aneurysms are associated with the greatest risk of paraplegia (Fig. 87-7). In the thorax, the recurrent laryngeal and vagus nerves are gently retracted off from the aorta. After cross-clamping of the aorta, the proximal anastomosis is sewn in an endoaneurysmal fashion (end-to-end within the aneurysm sac). All large intercostal arteries from T7 to L2 are reimplanted into the graft, followed by the visceral vessels. If stenoses at the origin of these arteries are encountered, an endarterectomy may be performed. Finally, the distal anastomosis is performed in endoaneurysmal fashion to an uninvolved portion of the distal aorta.

FIGURE 87-7 Crawford classification of thoracoabdominal aneurysms. Extent I, distal to the left subclavian artery to above the renal arteries. Extent II, distal to the left subclavian artery to below the renal arteries. Extent III, from the sixth intercostal space to below the renal arteries. Extent IV, from the 12th intercostal space to the iliac bifurcation (total abdominal aortic aneurysm). Extent V, below the sixth intercostal space to just above the renal arteries.

Indications

Asymptomatic TAAAs are repaired if the diameter exceeds 6 cm or if the rate of expansion exceeds 0.5 cm during a 6-month period. TAAAs presenting with abdominal or back pain are repaired immediately as there is an associated higher risk of rupture, especially in the setting of hypotension. Finally, aneurysms producing distal embolization may also be considered for repair regardless of size.

Contraindications

TAAA repair represents one of the most morbid vascular surgical procedures not only because of the risk of paraplegia (up to 13% electively) but also because of a mortality rate of 8%.¹² Patients with prohibitive cardiopulmonary risk are not candidates for this procedure. These patients are typically identified on preoperative cardiac stress testing as well as on preoperative pulmonary function testing. Relative contraindications include decreased life expectancy related to other medical issues.

Outcomes and Complications

The 30-day survival after TAAA repair is approximately 95%. Late survival rates are 55% at 5 years, 29% at 10 years, and 21% at 15 years.¹² Complications related to the surgery are typically pulmonary (32%), cardiac (8%), renal (6%), and spinal (4% to 13%) in nature. Spinal cord ischemia is significantly increased in Crawford extent I and II aneurysms.

Imaging Findings

Description

Thoracic aortic aneurysm (TAA) repair is a morbid procedure because of the necessity for a median sternotomy or posterolateral thoracotomy. Whereas endovascular TAA repair avoids the need for these approaches, anatomic factors such as small access vessels may preclude this. In these cases, hybrid TAA repair may be performed by creating open vascular surgical access to the aorta either distally or proximally. In the case of distal open access, an aortofemoral bypass may be performed either alone or in conjunction with concomitant debranching or repair of an aortic aneurysm (Fig. 87-8). The common iliac artery is oversewn, allowing retrograde blood flow through the aortofemoral limb to the internal iliac artery through the external iliac artery. In the case of proximal access, the arch vessels are debranched from the aorta and reanastomosed to a four-branched prosthetic graft that is anastomosed directly to the ascending aorta (Fig. 87-9). The sheath is then advanced through one of the limbs of the graft, and the TAA is repaired in standard endovascular fashion. At the conclusion of the case, the access limb of the graft is oversewn.

FIGURE 87-8 Preoperative three-dimensional postprocessed views from CTA of a patient with an abdominal aortic aneurysm (A) and thoracoabdominal aortic aneurysm (B). The patient underwent open debranching of the celiac, superior mesenteric, and bilateral renal arteries with a branched graft from the distal aorta (C and D, small arrow). A distal aorto–left femoral graft was also placed that was used for access in the subsequent endovascular repair (C and D, large arrow).

FIGURE 87-9 Preoperative CTA (A, oblique sagittal three-dimensional view) of a patient with a thoracic aortic artery aneurysm whose iliac arteries were smaller than the device diameter. A four-limbed bypass was anastomosed to the ascending aorta for device access as well as for debranching of the arch vessels (B). Postoperative CTA reveals endovascular exclusion of the aneurysm as well as the three-limbed bypass (C, oblique coronal three-dimensional view).

Indications

Endovascular repair of thoracic aneurysms may be limited by device sheath diameter that exceeds the diameter of the access arteries or heavy calcification and tortuosity of the access arteries. In these circumstances, hybrid repair of TAA may be useful. Patients must have TAA morphology that is suitable to endovascular repair.

Contraindications

Contraindications to hybrid TAA repair include cardiopulmonary risk factors as well as anatomic factors of the thoracic aneurysm. Currently, only three devices have been approved by the Food and Drug Administration for endovascular TAA repair (Cook TX, Gore TAG, and Medtronic Talent devices). Anatomic requirements include 20 mm or more of proximal and distal neck length and distal neck diameters of 20 to 42 mm. In cases in which the left subclavian artery needs to be covered with the endovascular stent graft for proximal fixation, contraindications to covering the left subclavian artery with the endograft include a patent left internal mammary artery to left anterior descending coronary artery bypass, incomplete circle of Willis, and dominant left vertebral artery. These factors increase the risk of myocardial infarction and stroke.¹³ Otherwise, most patients have enough collateral circulation to prevent left upper extremity ischemia, with claudication developing in approximately 16% and rest pain in 5%.¹⁴ In patients with upper extremity rest pain or tissue loss, a left carotid–subclavian bypass may be performed.

Outcomes and Complications

Outcomes of hybrid TAA repairs are similar to those of standard endovascular TAA repair. In the perioperative period, 10% of patients require reintervention; freedom from reintervention approaches 81% by 48 months.¹⁵ Spinal cord ischemic complications, which may occasionally be transient, are experienced by 7% of patients. The perioperative mortality rate is approximately 10% and is half that of an open repair.

Imaging Findings

Description

Open repair of abdominal aortic aneurysm (AAA) can be carried out through a midline or retroperitoneal approach; the choice of approach depends on factors related to aneurysm anatomy, involvement of the distal right iliac system, and previous abdominal surgeries. With either procedure, proximal and distal control of the aorta and iliac arteries is obtained. The proximal aortic clamp must be placed on a portion of aorta free from disease. In the case of juxtarenal and suprarenal aneurysms, a supraceliac clamp must be placed. An infrarenal artery clamp is placed just distal to the left renal vein in the case of an infrarenal aneurysm. The aneurysm sac is then opened longitudinally. If a supraceliac clamp is in place, the renal arteries are often flushed with iced heparinized saline to prevent ischemic damage. The proximal anastomosis is sewn in an endoaneurysmal fashion. The visceral vessels may be reimplanted on the graft if that portion of the aorta is aneurysmal. The proximal clamp is then removed and placed on the proximal graft, reestablishing blood flow to the kidneys in the case of supraceliac clamping. All backbleeding lumbar arteries are suture ligated. The inferior mesenteric artery, if patent, may be ligated in the presence of strong backbleeding or reimplanted in the presence of poor backbleeding. The distal anastomoses are then performed in a similar endoaneurysmal fashion. All clamps are removed, and blood flow is reestablished to the lower extremities. Finally, the aneurysm sac is closed over the graft to prevent contact with and possibly erosion into surrounding structures postoperatively.

Indications

The size at which asymptomatic AAA repair is indicated is determined by a composite of the morphology and anatomy of the aneurysm, the medical comorbidities of the patient, and the morbidity and mortality demonstrated by the surgeon. Broadly speaking, 5.5 cm is the size at which the risk of death from the surgical procedure (1% to 5%) is outweighed by the annual risk of rupture (5% to 10%). Other patient groups who may be repaired before this include women with 5-cm AAAs, who have a higher risk of rupture with smaller aneurysm size, and patients with a rapidly expanding AAA (>1 cm per year). According to the Aneurysm Detection and Management (ADAM) study¹⁶ and the U.K. Small Aneurysm Trial,¹⁷ AAAs between 4.5 and 5.5 cm can be safely observed in compliant patients as the risk of open surgery outweighs the risk of rupture. Symptomatic AAAs presenting with abdominal or back pain are repaired immediately as discussed previously for thoracoabdominal aneurysms.

Contraindications

Absolute contraindications to repair of AAA include prohibitive cardiopulmonary risk of surgery; a relative contraindication is decreased life expectancy related to other medical issues. Operative risk is increased in patients with chronic renal insufficiency, chronic obstructive pulmonary disease, congestive heart failure, moderate to severe coronary artery disease, and advanced age.

Outcomes and Complications

Long-term durability of open repair of AAA is excellent, and frequent surveillance is unnecessary. The 30-day mortality of patients undergoing open AAA repair is approximately 5% or less, and the 5-year survival is approximately 70%.

Complications related to AAA repair can be divided into early and late categories. Early complications include, but are not limited to, cardiopulmonary complications, renal failure, distal embolization of thrombus, hemorrhage, and colonic ischemia.

Late complications of AAA repair occur in approximately 7% of patients within 5 years. Aortic graft infection is a dreaded complication. Patients frequently present with fever, bacteremia, or failure to thrive. CT findings include air or fluid around the graft and inflammatory changes in normal tissue planes (Fig. 87-10). Patients undergoing AAA repair may normally have perigraft fluid up to 6 months postoperatively. Differentiation between a graft infection and normal postoperative fluid collections can be accomplished with CT-guided aspiration or indium In 111–tagged white blood cell nuclear scintigraphy.

FIGURE 87-10 Postoperative CT scan of a patient who underwent abdominal aortic aneurysm repair showing air within the aneurysm sac (arrow), consistent with graft infection.

Anastomotic pseudoaneurysms occur in 0.2% of aortic anastomoses, 1.2% of iliac anastomoses, and 3% of femoral anastomoses.¹⁸ This incidence increases over time, which stresses the importance of follow-up in young patients undergoing AAA repair.

Aortoduodenal fistulas occur approximately 0.9% of the time after AAA repair. Whereas these frequently present as a gastrointestinal bleed, the finding of intravenous contrast agent in the bowel lumen on an intravenous contrast–enhanced only CT scan (no oral contrast agent administered) should alert to this possibility. Emergent upper endoscopy for confirmation of the diagnosis, followed by extra-anatomic bypass and resection of the graft, is warranted.

Imaging Findings

Preoperative Planning

Similar to preoperative TAAA planning, CTA is often the preferred modality for preoperative planning before AAA repair. Not only does it provide a more accurate diameter measurement than ultrasonography, but it assesses the entire aorta for pathologic changes (Fig. 87-11A). CTA can identify heavy calcification, accessory renal vessels, and retroaortic left renal veins, all of which have implications for intraoperative clamp placement. The recent improvements in three-dimensional image postprocessing and reconstruction of CTA data have enhanced the ability of the vascular surgeon to assess aortic disease and to plan open repair by longitudinally distinguishing intraluminal thrombus from calcification as well as noncircumferential dilation of the aortic wall that might not be as easily seen on standard axial CT images.

FIGURE 87-11 A, Preoperative three-dimensional oblique frontal view from CTA in a patient with an abdominal aortic aneurysm. The patient underwent open aneurysm repair with ligation of the distal left common iliac artery, endarterectomy of the proximal left external iliac artery due to heavy calcification precluding standard anastomosis, and femoral anastomosis of the left graft limb. B, Postoperative image shows the aneurysm repair with retrograde flow through the left external iliac artery into the left internal iliac artery.

MRA, although not as commonly used as CTA, may also be used for preoperative planning, especially in patients with an allergy to iodinated contrast agents. Angiography is useful when there is suspicion of concomitant renal occlusive disease, renovascular hypertension, or other small-vessel anatomy that is often not well delineated by CT.

Postoperative Surveillance

Postoperative assessment of AAA repair is accomplished almost exclusively with CTA (Fig. 87-11B). Open AAA repairs are typically scanned once at 6 to 12 months after surgery, if there are no anatomic concerns. Further scanning is indicated for the development of late symptoms. CTA is helpful not only in assessing the durability of the repair but also for identifying aneurysmal degeneration of the remaining abdominal aorta and its branches, especially the iliac arteries (Fig. 87-12). This becomes clinically relevant beyond 3 mm of dilation and is seen in approximately 13% of patients.²⁰

FIGURE 87-12 Postoperative contrast-enhanced CT scan of a patient who 8 years previously underwent an abdominal aortic aneurysm repair with ligation of both internal iliac arteries and anastomosis of the graft limbs to the femoral arteries (small arrows). The patient was found to have expansion of the internal iliac artery aneurysms (large arrows) due to retrograde flow from pelvic collateral circulation.

Description

Open access of the iliac arteries may be necessary for endovascular abdominal aortic aneurysm repair (EVAR). This is accomplished through a flank retroperitoneal incision. Vessels are palpated to identify an area that is not heavily calcified. Proximal and distal control of the vessels is then obtained for introduction of the device in a manner similar to that for standard EVAR.

In patients with AAA and bilateral common iliac artery aneurysms, hybrid repair may be performed by a femorofemoral bypass, followed by an aorto–uni-iliac endograft and then either a contralateral external to internal iliac covered stent or ligation of the contralateral common iliac artery (Fig. 87-13).

FIGURE 87-13 Preoperative three-dimensional view of CTA (A, frontal view; B, caudocranial view) in a patient with concomitant abdominal aortic and bilateral common iliac artery aneurysms. The patient underwent a hybrid AAA repair with a femorofemoral bypass, open ligation of the left common iliac artery, and aorto–right external iliac unibody endografting (C). Other options for this patient would have included a hybrid AAA repair with a femorofemoral bypass, aorto–right external iliac unibody endograft, and right external–internal iliac artery covered stent (D).

Indications

Hybrid procedures for AAA repair may be performed for technical issues when the femoral or iliac access vessels are smaller than the EVAR device diameter, heavily calcified, or tortuous. Hybrid AAA repair may also be performed in patients with concomitant bilateral common iliac artery aneurysms and inadequate distal landing zones (Fig. 87-13A and B). In these patients, standard EVAR covering both internal iliac arteries with the endograft limbs would lead to a high likelihood of pelvic ischemia. Hybrid repair is useful in these situations to avoid the morbidity of an open repair.

Hybrid repairs may also be necessary when there is abnormally low takeoff of a renal vessel or a dominant accessory renal artery (Fig. 87-14). In these situations, an aortorenal or iliorenal bypass may be necessary before the placement of the endograft.

FIGURE 87-14 Preoperative three-dimensional view of CTA in a patient with an infrarenal abdominal aortic aneurysm and bilateral common and internal iliac artery aneurysms with an accessory right renal artery originating from the aneurysm sac (A). The left internal iliac artery aneurysm had been previously coil embolized. The patient underwent a hybrid AAA repair (B). A bypass from the right external iliac artery to the accessory right renal and inferior mesenteric arteries was performed before endografting to preserve blood flow to the right kidney and pelvis. The aneurysm was then repaired with a standard endograft whose distal limbs covered both internal iliac arteries.

Contraindications

Contraindications to EVAR with hybrid techniques are similar to those of standard AAA repair, although clamping of the iliac arteries is not associated with as high a morbidity as is clamping of the abdominal aorta.

Outcomes and Complications

Outcomes of hybrid AAA repairs are similar to those of standard EVAR.

Imaging Findings

Description

The aorta is accessed through a transperitoneal approach, and the femoral arteries are controlled by bilateral femoral cutdowns. Preoperative planning and the surgeon’s preference determine the nature of the proximal anastomosis: end to end or end to side. End-to-side proximal anastomoses preserve pelvic blood flow; end-to-end proximal anastomoses may be preferred to maximize blood flow to the lower extremities in patients with complete occlusion of the aorta and internal iliac arteries. Once the proximal anastomosis is complete, the limbs of the bifurcated graft are tunneled just anterior to the native common and external iliac arteries, posterior to the ureters, and then under the inguinal ligament. The femoral limbs are then anastomosed to the common femoral arteries.

Indications

Aortobifemoral bypass is performed in patients with disabling or lifestyle-limiting claudication, rest pain, or tissue loss and TransAtlantic Intersociety Consensus (TASC) D aortoiliac occlusive disease. In younger patients or those without prohibitive operative risk, aortobifemoral bypass may be more appropriate than endovascular revascularization because of improved long-term patency for TASC C disease.

Contraindications

Aortobifemoral bypass is associated with significant cardiopulmonary morbidity. Patients with cardiopulmonary comorbidities prohibitive of general anesthesia are not candidates for this procedure. Such patients are better served with extra-anatomic bypass despite the decreased patency rates of these procedures.

Outcomes and Complications

Outcomes of aortobifemoral bypass are excellent, with 5-year patency rates ranging from 85% to 95%. Complications occur infrequently and are typically cardiopulmonary and renal in nature. One unique complication related to this procedure is the development of thigh and buttock claudication in up to 30% of patients undergoing aortobifemoral bypass.²¹ This occurs because of a lack of blood flow in the hypogastric system and may be increased in patients with an end-to-end proximal anastomosis. Operative mortality rates range from 2% to 3%.

Imaging Findings

Preoperative Planning

Angiography is the gold standard for preoperative planning because it can show the precise pattern of disease and may assess the patency of the internal iliac arteries. In cases of complete aortic or bilateral iliac artery occlusion, brachial access may be necessary to evaluate the aorta proximal to the occlusion (Fig. 87-15).

FIGURE 87-15 Digital subtraction angiography demonstrating complete aortic occlusion.

Ultrasonography may be used to evaluate femoral anatomy when there is uncertainty of distal external iliac patency or poor imaging of femoral area based on poor delivery of contrast material.

MRA or CTA can be useful for the assessment of patients who have complete occlusion of the bilateral iliac arteries, which would prevent catheter angiographic assessment of the proximal abdominal aorta. CTA can also help delineate aortic thrombus and calcification, both of which have implications in intraoperative aortic clamp placement. MRA provides a viable option for patients in whom the administration of iodinated contrast agents is not desired.

Postoperative Surveillance

Postoperative surveillance may be performed with noninvasive vascular laboratory testing. Duplex ultrasonography can be used to assess graft patency, although this may be limited by bowel gas. More detailed information about graft patency is typically obtained with CTA or MRA. In patients without an iodinated contrast agent allergy, CTA has the advantage of being performed typically in a timelier manner. Compromise of graft patency requires angiographic assessment for anastomotic or intraluminal narrowing amenable to open or endovascular therapies. Finally, more distal peripheral vascular disease may lead to increased resistance within a graft limb and subsequent thrombosis (Fig. 87-16). Evaluation of lower extremity blood flow may be prudent in patients at risk for graft failure.

FIGURE 87-16 Postoperative contrast-enhanced CT image shows an occluded left aortobifemoral bypass limb (arrow). The patient subsequently underwent left above-knee amputation.

Description

Lower extremity bypass is performed in a variety of manners and is beyond the scope of this chapter. Factors common to all lower extremity bypasses are determination of inflow and outflow vessels, determination of adequacy of the runoff, and choice of conduit. An inflow vessel is defined as the blood vessel of the proximal anastomosis and generally refers to the adequacy of blood flow to the level of the inguinal ligament. Inflow vessels should not have any proximal stenoses that may compromise the blood flow into the conduit. The common femoral artery is most frequently used as inflow, but any artery with in-line flow from the aorta may be used. More distal vessels should be considered to decrease the length of the bypass, a factor associated with increased vein bypass thrombosis. The outflow vessel is defined as the blood vessel of the distal anastomosis. This is generally the most proximal vessel with in-line flow to the foot. Runoff may be defined as continuity of the outflow vessel with the foot or, for the peroneal artery, a direct communication between the delta branches and a pedal vessel. Finally, conduits may be autogenous or nonautogenous. Autogenous conduits include the greater and lesser saphenous veins as well as the basilic and cephalic veins of the arm. Nonautogenous conduits are typically made of polytetrafluoroethylene (PTFE) or polyester.

Once these factors have been determined, the inflow and outflow arteries are controlled both proximally and distally. An arteriotomy is made in the inflow artery, and the conduit is sutured to the artery in continuous fashion. Attention is then turned to the distal anastomosis, where the conduit is sutured in a similar manner. Adequacy of the bypass may be determined with intraoperative arteriography or Doppler ultrasound augmentation with graft compression.

Indications

Indications for lower extremity bypass are disabling or lifestyle-limiting claudication, rest pain, and tissue loss. Bypasses are not typically performed on patients with intermittent claudication; only 20% of these patients will progress to critical limb ischemia during a 10-year period. For these patients, lifestyle modification and exercise are the mainstays of therapy. Endovascular revascularization may also be considered for claudicants, depending on the anatomy and other clinical circumstances.

Contraindications

Contraindications to lower extremity bypass are rare and include cardiopulmonary disease prohibiting anesthesia and untreated hypercoagulable states.

Outcomes and Complications

Outcomes of lower extremity bypass are summarized in Table 87-2. The patency rates of this meta-analysis show that vein bypasses are the conduit of choice.

TABLE 87-2 Summary of Patency Rates in Patients Undergoing Lower Extremity Bypass

Complications of lower extremity bypass can be divided into graft-related and non–graft-related categories. Graft thrombosis is the most common complication and a major reason for postoperative graft surveillance (Fig. 87-17). Early graft thrombosis (0 to 30 days) is most likely due to technical error in either performance of the bypass or determination of adequacy of the runoff. Mid graft thrombosis (30 days to 2 years) is typically due to intimal hyperplasia. Late graft thrombosis is usually due to progression of atherosclerosis. Graft infection is another graft-related complication. Infections of autogenous grafts may be treated with antibiotic therapy. Attempts at salvage of infected prosthetic grafts can be made, although these frequently need to be excised, especially with involvement of an anastomosis. Fluid collections surrounding a graft on duplex ultrasonography or CTA may be suggestive of graft infection (Fig. 87-18). Non–graft-related complications are typically cardiopulmonary or renal in nature.

FIGURE 87-17 Digital subtraction angiography showing thrombosis of a prosthetic popliteal dorsalis pedis bypass (arrow).

FIGURE 87-18 Axial image from CTA shows a thrombosed lower extremity bypass with intraluminal air and surrounding fluid collection (arrow) consistent with graft infection.

Imaging Findings

Preoperative Assessment

Doppler ankle pressure measurements are the most commonly used noninvasive vascular laboratory tests to assess for peripheral vascular disease. The ankle-brachial index is determined by dividing the systolic blood pressure in the brachial artery by the systolic blood pressure at the ankle (the higher of the two values for the dorsalis pedis artery and the posterior tibial artery). The ankle-brachial index has been correlated to degree of symptoms (Table 87-3). The ankle-brachial index may be falsely elevated in heavily calcified arteries, as is typically seen in diabetic patients. Finally, in patients with claudication, the ankle-brachial index may be normal at rest but decreased with exercise. An abnormal exercise response is defined as a 20% decrease from baseline or more than 3 minutes to recover to baseline.

TABLE 87-3 Ankle-Brachial Indices and Correlation to Symptoms

Symptom	Ankle-Brachial Index
Normal	0.80-1.0
Claudication	0.50-0.60
Critical ischemia	<0.30

Measurement of pulse volume recordings in the lower extremity is a useful technique to identify significant stenosis in the lower extremity (Fig. 87-19). Blunting of the normal cardiac cycle waveform is typically seen distal to a hemodynamically significant stenosis.

FIGURE 87-19 Pulse volume recordings in a patient with lower extremity disease. Note the failure to augment between the brachial and femoral pressures, signifying aortoiliac disease on the left, and blunting of the waveform below the femoral artery, signifying left superficial femoral artery disease.

Transcutaneous oxygen tension (TcPo₂) measurements are particularly helpful in determining the ability of a wound to heal (Table 87-4). TcPo₂ quantifies oxygen molecules transferred to the skin after it is heated with a transducer above 40°C. TcPo₂ can be in the form of absolute oxygen tension or regional index, the TcPo₂ of the leg divided by the TcPo₂ measured at a reference point (chest). This technique has also been shown to be useful in diabetic patients, in whom the ankle-brachial index is unreliable.²²

TABLE 87-4 Transcutaneous Oxygen Measurements and Correlation to Symptoms

Symptom	Transcutaneous Oxygen Tension (absolute)	Transcutaneous Oxygen Tension (regional index)
Likely to heal	35-40 mm Hg	>0.6
Borderline or delayed healing	25-35 mm Hg	0.4-0.6
Unlikely to heal	<20-25 mm Hg	<0.4

Preoperative Planning

Preoperative planning for a lower extremity bypass is typically performed by use of catheter angiography, but CTA and MRA have emerged as suitable preoperative planning examinations at some sites. Preoperative planning requires the vascular surgeon to identify the exact location of stenoses but also to assess the inflow (site of proximal anastomosis), outflow (site of distal anastomosis), and runoff vessels (arterial tree beyond the distal anastomosis) (Fig. 87-20). Runoff scores have been shown to be one of the strongest predictors for bypass patency and are a key consideration during angiography.²³

FIGURE 87-20 Digital subtraction angiography showing poor runoff in a patient with toe gangrene. The patient underwent femoral-distal bypass to the dorsalis pedis artery augmented with a distal arteriovenous fistula to improve flow through the bypass.

Preoperative vein mapping with duplex ultrasonography can provide detailed information about the quality of a potential vein graft. It can detect constriction of veins secondary to sclerosis, previous manipulation, or thrombophlebitis. It can also assess length and diameter of the vein. These measurements can be particularly important in performing a tibial bypass for which a long segment may be necessary. Diameters of more than 3 mm for reverse²⁴ and 2 mm for in situ²⁵ saphenous vein grafts have been recommended to obtain adequate long-term patency.

Postoperative Surveillance

Long-term follow-up of lower extremity bypasses is aimed at early identification of a failing graft and is critical to the long-term success of all lower extremity bypasses as restenosis is frequent. Duplex ultrasonography is frequently used to interrogate a bypass and to identify areas of stenosis with increased velocities (Fig. 87-21). Duplex ultrasonography may also show significantly decreased velocities throughout the graft that may be related to a distal anastomotic stenosis or worsening of the runoff arterial bed. Once a failing graft is identified, angiography must be performed to more accurately delineate the problem. Revision may be performed with both open and endovascular techniques.

FIGURE 87-21 Duplex ultrasonography of a lower extremity bypass graft stenosis. Note the elevated velocities across the stenosis.

Description

Hybrid procedures for aortoiliac and lower extremity peripheral vascular disease typically involve open access to the femoral arteries for subsequent endovascular intervention either proximally or distally. Open access of the femoral arteries is performed through a standard cutdown technique. Proximal and distal control of the vessel is obtained with vessel loops. This technique allows direct palpation of the artery and identification of an area that is not heavily calcified, and thus it is more appropriate for control with a vascular clamp. At the end of the procedure, the femoral plaque endarterectomy is performed and the vessel is closed with patch angioplasty.

Indications

Patients with heavily calcified femoral arteries are at higher risk of plaque dissection or embolization with percutaneous endovascular interventions. These patients are candidates for open angioplasty. At the conclusion of the procedure, a femoral thromboendarterectomy may serve to increase inflow into the lower extremity.

Contraindications

Open angioplasty can be safely performed with sedation and local anesthesia and thus has few contraindications.

Outcomes and Complications

Outcomes and complications of hybrid procedures are identical to those of their percutaneous counterparts.

Imaging Findings

Preoperative Planning

Duplex ultrasonography or arteriography of the femoral arteries typically shows heavy calcification (Fig. 87-22).

FIGURE 87-22 Digital subtraction angiography showing heavy calcification of the common femoral artery. Open angioplasty allows the surgeon to perform an iliofemoral endarterectomy at the conclusion of the case and thus to improve inflow.

Postoperative Surveillance

Postoperative surveillance is similar to that for endovascular interventions and is discussed in a separate chapter.

KEY POINTS

Different imaging modalities are relevant at different points during the course of vascular surgical disease management. An understanding of their utility at each point is key to the care of the vascular surgical patient.

Duplex ultrasonography is useful in the preoperative and postoperative care of patients with carotid artery disease as well as in the follow-up of lower extremity bypass.

Three-dimensional CT angiography is becoming the preferred modality for preoperative planning of aortic aneurysmal disease because of its ability to provide accurate diameter measurements as well as to assess for other aortic disease.

Magnetic resonance angiography is a useful adjunct, especially in cases of chronic renal insufficiency.

Catheter angiography remains the gold standard for the evaluation of lower extremity occlusive disease. Angiography is also useful in cases in which the results of noninvasive imaging studies are discordant.