Microsurgical carotid endarterectomy

Microsurgical Carotid Endarterectomy Nicholas Theodore, MD, Jonathan J. Baskin, MD, Robert E Spetzler, MD, A. Giancarlo Vishteh, MD, Paul J. Apostolides, MD, 1 and Martin C. Holland, MD 2

Microsurgical carotid endarterectomy has become an established procedure in the prevention of cerebrovascular accidents in select patients. The anatomy relevant to this procedure is described, and the preferred operative technique of the senior author is detailed. Copyright 9 1998 by W.B. Saunders Company

s with all surgical procedures, careful preparation and attention to detail are critical to ensure favorable outcomes after microsurgical carotid endarterectomy. ~ This article reviews the technique of microsurgical carotid endarterectomy, including relevant anatomy and potential complications.

Operating Room Setup Immediately before the patient is taken to the operating room, their symptoms should be reviewed and an updated neurological examination performed. This step is necessary to determine if the patient's status has changed since his or her previous examination and to verify the correct side for surgery. In the standard operating room setup, the neuroanesthesiologist is positioned at the head of the bed. There should also be sufficient space for the operating microscope to enter the surgical field from this position (Fig 1). Additional working space should be allotted for the electrophysiology technologist and his or her equipment. Before anesthesia is induced, baseline neuroelectrophysiological data should be recorded. A working knowledge of this technology and continual communication between the neurophysiologist and surgeon during the procedure are essential to detect early changes in signals that suggest cerebral ischemia and could warrant specific actions by the surgeon and anesthesiologist.

Surgical Technique As with all neurosurgical procedures, the patient's identity and correct side for surgery should be confirmed immediately before the patient is positioned. All members of the operating

From the Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ. Address reprint requests to Robert F. Spetzler, MD, c/o Neuroscience Publications, Barrow Neurological institute, 350 W. Thomas Road, Phoenix, AZ 85013-4496. 1Current address: Orthopedic & Neurological Surgery Specialists, 6 Greenwich Office Park, Greenwich, CT 06831. 2Current address: Highland General Hospital, 1411 E. 31st Street, Oakland, CA 94602. Copyright 9 1998 by W.B. Saunders Company 1092-440)(/98/0104-000458.00/0

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room team should be familiar with this information and should participate in ensuring that appropriate orientation to the side of the pathology is maintained.

Positioning The patient is placed in the supine position with the head supported on a foam or gel "doughnut." The head is turned slightly away from the operative side. An interscapular roll is sometimes helpful for producing mild cervical extension that facilitates access to the carotid circulation, especially in the case of obese patients. Given the advanced age of this operative population, particular care is taken to avoid hyperextension of the neck that could produce cervical spinal cord injury. The ear, retroauricular, mandibular, neck, and upper chest regions are then prepared and scrubbed with a povidone iodine solution. The neck should not be scrubbed excessively to avoid dislodging atheromatous material from the diseased carotid artery. The lower leg should also be prepared when the need for a saphenous vein patch graft is anticipated.

Incision Before the patient is draped, the incision line is marked with a sterile pen and infiltrated with 0.5% lidocaine with 1:200,000 units of epinephrine. The classically described incision follows the anterior border of the sternocleidomastoid muscle (SCM) and is extended to within 3 cm of the clavicle and the angle of the jaw. If necessary, this incision can be enlarged by curving it superiorly and posteriorly toward the mastoid tip (Fig 2). The senior author (RFS) prefers to use an extended transverse incision along a skin crease. The incision begins near the midline and is brought to just past the anterior border of the SCM centered over the region of the bifurcation of the common carotid artery (CCA). At our institution, this level can be identified on magnetic resonance (MR) angiography scout images that allow the vertebral level corresponding with the carotid bifurcation to be determined (see the article Imaging of Extracranial Occlusive Vascular Disease in this issue). For bifurcations located at the mid- or lower cervical levels, the transverse incision offers more than adequate exposure and is cosmetically superior. For high bifurcations or stenosis of the internal carotid artery (ICA) that approaches the skull base, the longitudinal incision is used.

Exposure The skin is incised with a No. 10 blade down to the level of the platysma muscle. The bipolar electrocautery forceps and Bovie electrocautery or Shaw hemostatic electrical scalpel (Oximetrix, Mountain View, CA) are used to provide hemostasis throughout the procedure. Vigilant attention to hemostasis is

Operative Techniquesin Neurosurgery, Vol 1, No 4 (December), 1998: pp 1"78-184

Evoked potential & EEG monitoring

Jrgical icroscope Fig 1. The optimal operating room setup for performing a microsurgical carotid endarterectomy. This configuration allows both the neuroanesthesiologist and microscope to enter the surgical field from the head of the table. (Reprinted with permission from Barrow Neurological Institute.)

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essential to avoid bleeding difficulties following the required anticoagulation that precedes the carotid arteriotomy, The platysma is sectioned in the same direction as the initial skin incision by using sharp dissection or electrocauterization with the Shaw scalpel. Several nerves course through the plane between the platysma and SCM, including branches of cranial nerve (CN) VII and the upper three cervical roots. The marginal rrmndibular branch of CN VII supplies some of the perioral musculature and runs along the mandibular angle. Dissection or excessive retraction in this region should be avoided. The cervical branch of CN VII runs inferiorly and supplies the platysma. The transverse facial, greater auricular, and lesser occipital nerves emerge from the posterior aspect of the SCM. The lesser occipital and greater auricular nerves innervate the skin around the occipital area laterally and the ear inferiorly, respectively. The transverse facial nerve swings anteriorly to innervate skin within the anterior cervical triangle. A transverse incision helps to avoid injury to these structures. However, exposure should not be compromised to preserve these cutaneous nerves. Other anatomic structures in this surgical plane include superficial cervical lymph nodes, the parotid gland, and superficial draining veins of the external jugular system. Small lymph nodes have a tendency to bleed profusely and should be dissected medially and retracted laterally. If encountered, the parotid gland should be carefully retracted ventromedially. The carotid sheath runs deep to the superficial layer of .the cervical fascia (Fig 3). The sheath contains the following MICROSURGICAL CAROTID ENDARTERECTOMY

Fig 2. The carotid artery can be exposed with an anterocervical longitudinal incision parallel to the medial border of the SCM. However, we prefer a transverse incision (dashed line) made by using a skin crease based on the level of the carotid bifurcation as shown on preoperative imaging studies, We prefer the latter incision because cosmesis is better. (Reprinted with permission from Barrow Neurological Institute.) 179

Fig 3. Exposure of the carotid sheath and its contents (including the carotid artery and its bifurcation), the common facial and internal jugular veins, and CN X. Before the final retractor is placed, the common facial vein and other smaller venous tributaries are ligated and sectioned to afford better exposure. (Reprinted with permission from Barrow Neurological Institute.)

structures: CNs X and XII; the superior and inferior roots of the ansa cervicalis; the internal jugular vein, CCA, ICA, and carotid bifurcation. The nerves enter and exit the sheath at various levels whereas the vascular structures stay within it along their entire course. The carotid sheath is opened by sharply incising the fascia along the anterior border of the SCM, preferentially starting over the CCA or its bifurcation. The sheath is carefully opened superiorly toward the posterior belly of the digastric muscle, which is a good landmark for the superior extent of the exposure. Inferiorly, exposure to the level of the omohyoid muscle typically provides adequate proximal exposure of the CCA. If necessary for exposure, the omohyoid can be sectioned and later reapproximated with suture. The boundaries of exposure are tailored to the level of bifurcation and extent of atheromatous disease. Within the carotid sheath, the internal jugular vein lies anterolateral to the CCA. CN X typically runs between the two vessels in a posterior position. Veins that drain the face and anterior neck cross posteriorly t o drain into the internal jugular vein. The ansa cervicalis runs posteromedial to the vein in the groove anterior to the artery. CN XII typically runs high within the sheath and is lateral to both the ICA and external carotid artery (ECA). Its location may be variable as can the location of CN X. On entering the carotid sheath, the first maneuver is to address veins that hinder access to the carotid artery. The most prominent of these traversing veins is the common facial vein, which along with other veins that drain the face and anterior neck, should be identified, ligated, and cut. Occasionally, CN XII can adhere to the transverse facial vein. Dissection should therefore proceed cautiously to avoid inadvertent transection of the nerve. At this point, a blunt retractor (Weitlander type) can be placed along the medial border of the internal jugular vein to retract it laterally. Surgical fishhooks and a Leyla bar (Aesculap, San Francisco, CA) can be used to retract soft tissues superiorly and to gain exposure in this direction (Fig 4) .2 Care should be taken when placing the fishhooks to avoid injuring underlying structures. Extensive dissection along the posterior wall of the carotid is unnecessary and should be avoided because it jeopardizes nervous structures and risks embolization. The ansa cervicalis,

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which can be followed rostrally to identify CN XII, can be transected or mobilized and retracted anteromedially to provide better access to the carotid artery.

Endarterectomy A semirigid, 13-French MicroVac uhramalleable suction catheter (PMI Corp., Chanhassen, MN) is placed between the jugular vein and carotid artery and secured by using surgical staples to the draping material to provide continuous suction. The wound is irrigated, and hemostasis is evaluated as barbiturates are administered to induce burst suppression on compressed spectral analysis (CSA). At this time, a bolus of heparin (70 IU/kg) is administered to the patient. The ICA is temporarily clipped and the CSA assessed for changes. To avoid intracranial embolization, the CCA is never manipulated unless the ICA is occluded. An angled vascular clamp is placed across the proximal CCA, and the CSA and somatosensory evoked potential tracings are further observed for signs of ischemia. The operation proceeds if the tracings remain stable. If not, the blood pressure is increased. Intraluminal shunting is used (discussed later) only if asymmetry in the CSA persists after these maneuvers. Temporary aneurysm clips are placed across the distal ICA, ECA, and superior thyroid arteries (Fig 5). The carotid artery is then palpated gently to identify the extent of atheromatous disease. A surgical marker can be used to indicate the proposed arteriotomy and prevents the incision from drifting medially toward the carotid bulb, which makes performing a nonstenotic closure more difficult. The arteriotomy is started with a small incision in the distal CCA by using a No. 11 blade and is carried cephalad using Pott's scissors along the affected length of the ICA (Fig 6). The vessel is flushed continuously with heparinized irrigation (4,000 IU/L of normal saline) until the arteriotomy has been fully repaired. Most carotid endarterectomies in the United States are performed under loupe magnification. However, we prefer to use the superior illumination and magnification offered by the operating microscope. Given that two-thirds of postoperative strokes result from preventable technical errors such as carotid tears and intimal flaps, 3 every effort should be made to

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Fig 4. (A) Significantly enhanced exposure is provided by attaching fishhooks from the superior aspect of the wound to a Leyla bar (Aesculap, San Francisco, CA; compare with Figure 3). (B) Intraoperative photograph showing final placement of retractors and fishhooks immediately before the arteriotomy is begun. (Reprinted with permission from Barrow Neurological Institute.)

Fig 5. Immediately before the arteriotomy is performed, temporary vascular clips and a suction catheter are placed. (Reprinted with permission from Barrow Neurological Institute.)

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Fig 6. After an initial longitudinal incision is made in the proximal CCA with a No. 11 blade, the arteriotomy is completed in a cephalad direction just beyond the level of stenosis. (Reprinted with permission from Barrow Neurological Institute.)

optimize the extent of plaque removal and the quality of nonstenotic vessel repair. Nontoothed vascular forceps are used by the surgeon and assistant to grasp the vessel carefully. A No. 4 Penfield dissector is used to establish the plane around the plaque at the level of the CCA (Fig 7). The endarterectomy continues in a circumferential fashion, cephalad along the ICA and ECA. As the plaque tapers into the ICA and ECA, its removal is facilitated by everting the vessel and gently pulling the plaque away. The plaque can then be sharply removed with Pott's scissors at the level of the CCA (Fig 8). Once most of the plaque has been removed, the vessel wall is closely inspected for small pieces of residual plaque, which are removed carefully with forceps. This inspection is particularly important at both the proximal and distal ends where plaque or loosely adherent intima should be trimmed with microscissors (Fig 9). When identified, loose intimal flaps should be repaired with 8-0 monofilament tacking sutures, although this is rarely required in our experience.

Closure We close almost all carotid endarterectomies primarily, reserving patch grafting for specific cases (see the article Patch Graft Angioplasty Techniques for Extracranial Occlusive Vascular Dis-

Fig 7. After the endarterectomy, the plaque is removed circumferentially by using a No. 4 Penfield dissector. The dissection proceeds proximally to distally. The plaque within the ECA is removed by everting the artery and gently pulling the plaque away. (Reprinted with permission from Barrow Neurological Institute.)

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Fig 8. Pott's scissors are used to amputate sharply the portion of the plaque that extends into the proximal carotid artery. This maneuver minimizes turbulent flow at the proximal end and lowers the risk of thrombus forming at this site. (Reprinted with permission from Barrow Neurological Institute.)

Fig 9. After the plaque has been removed, the denuded arterial surface is inspected under the operating microscope. All loose debris is removed, and microscissors are used to trim the proximal and distal endarterectomy sites to eliminate abrupt transition zones between the in tima and plaque. (Reprinted with permission from Barrow Neurological Institute.)

ease in this issue), Closure of the arteriotomy begins at its distal end using 6-0 Prolene suture (Ethicon, Johnson and Johnson Professionals, Inc., Somerville, NJ) in a running, nonlocking fashion. The suture should never be grabbed or bent with an instrument as this can weaken its structural integrity. Similarly, a single suture line should not be tied to itself because of the risk of knot slippage. As each stitch is placed within a millimeter or two of the vessel edge, it is tightened and held out of the way with gentle manual traction applied by the assistant. When the closure is about half completed, a second suture is tied at the proximal end and run distally toward the first (Fig 10). During the arteriotomy closure, several milliliters of pure heparin (3,000 U) are instilled in the vessel lumen to minimize the risk of thrombosis. Care is taken to ensure that this heparin is irrigated out before the final stitch is placed to avoid an intracranial bolus. Before final closure, the temporary clip on the ICA is removed to permit backbleeding that expels air and loose debris through the open arteriotomy site. If backbleeding is weak or absent, the ICA must be reexplored immediately to look for residual plaque, an intimal 'flap, or distal thrombosis. If distal thrombosis is suspected, a balloon thrombectomy can be performed using a Fogarty catheter. This technique is deTHEODORE ET AL

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suture. Benzoin and sterile adhesive strips are placed over the wound before the surgical drapes are removed. A vascular stapling device is available as an alternative means of closing carotid arteriotomies. A recent review of this technique 4 shows that the risk of carotid arterial hemorrhage associated with this instrument is unacceptable. In addition, its cost is prohibitive.

Intraluminal Shunting

Fig 10. The arteriotomy is closed from the distal ICA toward the middle of the arteriotomy site. (Reprinted with permission from Barrow Neurological Institute.)

scribed more completely in the article Techniqueof Microsurgical Carotid Thromboendarterectomyin this issue. Once good backbleeding from the ICA has been attained, the clip is reapplied and the backbleeding technique is repeated with the CCA and ECA. As the closure is finalized, the clip on the superior thyroid artery is removed permanently to allow constant backbleeding. After the final stitch has been placed, the two ends of suture are tied together meticulously with at least five knots (Fig 11). The risk of sending embolic debris through the ICA can be minimized by removing the temporary clips in a specific order. The clip from the ECA is removed first. The CCA clamp follows to permit debris, blood, and trapped air to travel up the ECA preferentially. The CCA clamp is then replaced. Because blood flow in the ICA is usually greater than that in the ECA, the ICA clip is removed to send blood and debris trapped within the ICA out through the external circulation. Finally, the CCA clamp is removed to re-establish blood flow through the newly repaired carotid artery. The suture line is carefully inspected, and small bleeding points can be coagulated by using bipolar cauterization. Bipolar coagulation should not be used directly on the suture material, fnstead, slight oozing can often be overcome by covering the suture line with a small piece of compressed sheet microfibrillar collagen (Avitene, Davol Corp., Cranston, RI). The retractors and fishhooks are then removed and hemostasis is again obtained. Interrupted 3-0 Vicryl sutures are used to reapproximate the platysma. The skin is closed by using 3-0 Vicryl interrupted sutures in the deeper subcutaneous layer. The subcuticular layer is closed with a running 4-0 Vicryl

Fig 11. Closure is completed from the proximal common carotid with both sutures meeting in the middle. Prolene (6-0) is used in a running, nonlocking fashion with care exerted to avoid damaging the suture. (Reprinted with permission from Barrow Neurological Institute. MICROSURGICAL CAROTID ENDARTERECTOMY

Intraluminal shunts are flexible catheters placed across the endarterectomy site to preserve flow to the ipsilateral ICA (Fig 12). Although theoretically sound, these devices potentially increase the risk of air, plaque, and platelet emboli. 5,6 The use of shunts can also complicate plaque removal from the proximal and distal portions of the carotid artery and make closure difficult. Consequently, we do not routinely employ intraluminal shunts. We reserve their use for instances when neurophysiological monitoring suggests the presence of ischemia despite cerebral protection with barbiturates and induced hypertension. We have found it necessary to use shunting in less than 5% of patients undergoing carotid endarterectomy.

Surgical Complications Nerve Injuries Most nerve injuries are caused by traction or excessive manipulation during surgery and are therefore transient. The marginal mandibular branch is a commonly injured superficial nerve because it is often compressed against the angle of the jaw. Postoperatively, family may think that patients with a retraction injury of the marginal mandibular branch have suffered a stroke. The patient is left with paresis of the depressor anguli oris, depressor labia inferioris, and the mentalis muscles. (The ipsilaterality of the deficit, however, indicates a peripheral cause.

Fig 12. A soft flexible tube is passed from the proximal CCA to the distal ICA while the endarterectomy is being performed. Vessel loops are used to hold the shunt in place. 9Although the placement of shunts is theoretically sound, complications such as air, thrombus, and plaque emboli and intimal damage to the distal ICA make their routine use undesirable. (Reprinted with permission from Barrow Neurological Institute.) 183

The remaining nerves at risk are deep and lie adjacent to or within the carotid sheath. Overall, the most commonly injured nerve during carotid endarterectomy is CN XII. Its injury causes paresis of the ipsilateral tongue and produces speech and swallowing difficulties. CN X is seldom injured because its course is deep within the carotid sheath. Two of its branches, however, are vulnerable to injury: the superior and recurrent laryngeal nerves. The superior laryngeal nerve runs immediately deep to the superior thyroid artery and is occasionally injured when this vessel is temporarily clipped. Its injury leads to paresis of the cricothyroid muscle and inferior pharyngeal constrictors and loss of sensation to the ipsilateral epiglottis and larynx. These deficits can lead to significant difficulties with swallowing and aspiration. The recurrent laryngeal nerve runs deep within the groove between the trachea and esophagus and can be injured when the medial retractor blades are placed too deeply. When this nerve is injured, the intrinsic muscles of the larynx and vocal cords are weakened. Unilateral vocal cord paralysis and a concomitant hoarse voice can ensue.

Wound Hematomas The North American Symptomatic Carotid Endarterectomy Trial cited the incidence of wound hematomas at 5.5%. ~ Although most hematomas are clinically harmless, they can become life-threatening if the trachea or carotid artery is compressed. In cases of airway compromise, the wound should be opened immediately at the bedside. Less urgent evacuation should be performed in the operating room. Postoperative hematomas are associated with systolic hypertension, poor intraoperative hemostasis, and rupture of the carotid suture line. Carotid endarterectomies closed with a patch graft angioplasty are associated with a ruptured suture line more often than those closed primarily. 3,7

Neurological Deficits Neurological deficits can be immediate or delayed. Immediate deficits are usually related to intraoperative hypoperfusion, embolic events, or carotid thrombosis and are associated with carotid manipulation or cross-clamping. Patients who develop a neurological deficit immediately after surgery should be evaluated urgently to rule out carotid thrombosis. Computerized tomography of the head, carotid ultrasonography, and angiography can all be used to evaluate patients acutely. Occlusion of the carotid artery in the immediate postoperative

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period should be treated with reexploration and thrombectomy (see Technique of Microsurgical Carotid Thromboendarterectomy in this issue). Delayed neurological deficits can result from carotid thrombosis, hypotension, or postoperative intracerebral hemorrhage. The latter is often associated with cerebral hyperemia caused by increased perfusion pressure and impaired cerebral autoregulation. Although these complications cannot always be prevented, their early diagnosis is the cornerstone of effective therapy.

Postoperative Care After surgery patients are observed overnight in the intensive care unit so that their blood pressure, wound, and neurological status can be monitored closely. Patients are kept normotensive during this period and preoperative antihypertensive medications are restarted. Most patients are discharged home the morning after surgery. Aspirin (325 mg rectally), first administered in the recovery room, is continued daily.

Conclusion Carotid endarterectomy is a safe and effective procedure in the prevention of cerebrovascular accidents. Meticulous anesthetic and surgical technique, use of the operating microscope, and good postoperative care help ensure favorable outcomes.

References 1. North American Symptomatic Carotid Endarterectomy Trial Collaborators: Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med 325:445-453, 1991 2. Greene KA, Zabramski JM, Spetzler RF: Enhancing rostral exposure for carotid endarterectomy: Technical report. BNI Quarterly 14(3):1821, 1998 3. Rosenthal D, Archie JP, Jr., Garcia-Rinaldi R, et al: Carotid patch angioplasty: Immediate and long-term results. J Vasc Surg 12:326333, 1990 4. Findlay JM, Megyesi JF: Carotid arteriotomy closure using a vascular clip system. Neurosurgery 42:550-554, 1998 5. Loftus CM, Quest DO: Technical controversies in carotid artery surgery. Neurosurgery 20:490-495, 1987 6. Sundt TM, Jr., Ebersold MJ, Sharbrough FW, et al: The risk-benefit ratio of intraoperative shunting during carotid endarterectomy. Relevancy to operative and postoperative results and complications. Ann Surg 203:196-204, 1986 7. Holland MC, Spetzler RF: Carotid endarterectomy. Neuroimaging Clin N Am 6:929-956, 1996

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