Resection of Carotid Artery Aneurysms
Brandon W. Propper
Christopher J. Abularrage
Introduction
Extracranial carotid artery aneurysm (ECAA) is an uncommon clinical finding that requires comprehensive evaluation and meticulous operative care. Currently, operative treatment for ECAA comprises less than 1% of all surgery on the extracranial carotid arterial system. In the past, mycotic degeneration was a leading cause of aneurysm formation, but this etiology has declined secondary to antibiotic use for head and neck infections. Modern day ECAA formation most frequently represents atherosclerotic degeneration or traumatic injury.
Defining ECAA was historically a challenge as the normal common carotid artery (CCA) caliber can range from 30% to 50% greater than that of the distal internal carotid artery (ICA). The most widely accepted definition based on published vascular texts is that of de Jong and is defined as carotid bulb enlargement greater than or equal to 200% of the ICA diameter or bulb dilation of 150% or greater of the CCA diameter.
Indications/ContraindicationsIndications for repair and treatment are relatively broad as the consequences of future symptoms can be drastic. No long-term studies have evaluated medical therapy for patients diagnosed with ECAA and no accepted algorithm or treatment paradigm exists. Regardless of underlying etiology, the treatment is usually surgical; however, the surgeon must first consider the etiology to base operative planning.
Atherosclerotic Disease: For patients with age related disease or degenerative disease, ECAA should be repaired once identified and the size criteria are met. Degenerative aneurysms occur at the proximal ICA or distal CCA and are fusiform in nature. Enlargement can produce symptoms from embolic events or from compression. Embolic events results in stoke, whereas compression manifests as cranial nerve dysfunction, dysphagia or new palpable mass. Any symptoms related to aneurysmal change are indications for repair. It is also well accepted that once an aneurysm is identified based on size criteria, the risk of future stroke is high and warrants repair.
Table 1.1 Blunt Carotid Injury Grading System
I. Intimal injury or irregularity with less than 25% luminal compromise
II. Dissection or hematoma with over 25% luminal compromise
III. Pseudoaneurysm
IV. Carotid thrombosis
V. Complete transection
Traumatic Aneurysm: Traumatic aneurysm occurs secondary to penetrating or blunt trauma. Fortunately, most penetrating injuries are identified early and late formation indicates a missed injury. Conversely, blunt trauma creates a flexion–extension injury causing extracranial arterial dissections. With current practice guidelines CT angiography is widely used and identifies blunt carotid injury (Table 1.1). Grade III to V injuries are addressed emergently, however, low-grade injuries can be medically managed and require surveillance. Dissection with aneurysm formation or progressive dilation represents another indication for intervention. Any dissection, regardless of etiology has a tendency to propagate distally which makes subsequent repair challenging. Aneurysm repair in the setting of prior arterial dissection requires vigilant planning to establish a distal target with the potential need for high exposure.
Fibromuscular Dysplasia (FMD): The underlying etiology of aneurysm formation from FMD is similar to traumatic injury with dissection as an underlying cause. In contrast, FMD classically affects the distal ICA and aneurysm formation is high on the internal carotid. In addition, FMD alone is associated with saccular aneurysms of the distal ICA and intracranial aneurysms. Aneurysms of the distal ICA that encroach into the skull base are best addressed by a multidisciplinary team including vascular surgeons, neurosurgeons, and neurointerventionalists.
Postoperative carotid endartectomy (CEA): Pseudoaneurysmal change following CEA is a rare occurrence and should prompt evaluation for infection. With prosthetic patch, pseudoaneurysms present months to years after surgery and well past that of pseudoaneurysm from technical error. Venous patches are more resistant to infection, but aneurysmal change should warrant an infectious workup. It should be noted that previous use of certain (single layer superficial vein) venous patches has been associated with late aneurysm formation from noninfectious causes but still may warrant intervention.
Contraindications to surgical therapy are all relative. The major decision hinges on the individual patient’s overall medical health and ability to tolerate open surgical or endovascular therapy. One group of patients that deserve additional thought is those with contralateral carotid occlusion. While shunting is possible during surgery, some anatomy is unfavorable for shunt placement. Short distal ICA, extreme ICA tortuosity, previous distal dissections, and resection of long segments of carotid all make shunt placement difficult and potentially harmful. Patients with contralateral occlusion and anatomy unsuitable for shunting may be better suited with endovascular repair, or a higher threshold for any surgical intervention. However, most of the anatomic limitations for open surgery are similarly challenging for endovascular treatments. No clear guidance exists for these challenging scenarios and they must be addressed individually.
Preoperative PlanningRegardless of underlying etiology, preoperative planning is essential to mitigate complications for an otherwise risky procedure. Routine carotid duplex ultrasound (DUS) is often the initial diagnostic modality used to evaluate ECAA. When performing DUS, it is important to note abnormalities in anatomy secondary to aneurysm growth including displacement of the jugular vein, elongation of the ICA, and displacement of the
carotid bulb. Identifying a proximal clamp site and evaluating flow parameters in the CCA, ICA, and proximal external carotid artery (ECA) should all be noted.
carotid bulb. Identifying a proximal clamp site and evaluating flow parameters in the CCA, ICA, and proximal external carotid artery (ECA) should all be noted.
Where DUS fails for ECAA is the distal ICA. Further imaging is almost always warranted to identify the distal extent of aneurysmal disease, dissection progression, and concomitant intracranial disease. Although angiography remains the gold stand for evaluation of luminal arterial flow, the true extent of aneurysm degeneration may be missed with angiography. Furthermore, the surrounding structures cannot be visualized on angiogram. Both computed tomographic angiography (CTA) and/or magnetic resonance angiography (MRA) are preferred prior to angiography during the initial workup. Angiography should be reserved where questions remain with regard to anatomy, stenosis, and patency. The following are specific preoperative factors that should be considered when looking at preoperative imaging:
Proximal CCA disease and clamp site: The proximal CCA is usually long and has significant room for both a clamp and sewing ring, but the surgeon should evaluate for significant stenosis and the relationship of the aneurysm to the carotid bulb. The total distance between the proximal CCA and distal ICA alters decisions regarding bypass versus transposition. In addition, the size of the proximal ICA or CCA should be noted so that an appropriate size conduit can be selected. Gross size discrepancy between the large arterial inflow (CCA) and venous conduit should be avoided when possible. Ultrasound should be used liberally for preoperative vein mapping of the saphenous vein, deep femoral vein, and ipsilateral jugular vein. If a size discrepancy exists between the vein and artery, prosthetic tube grafts have excellent patency and can be selected for appropriate size match.
Distal internal carotid artery length: This is often the most crucial portion of the preoperative evaluation, especially with previous dissection and FMD, as the distal carotid may contain existing disease complicating surgery. High exposure (Table 1.2) should be expected and imaging can delineate what exposure is required. The surgeon should err on the side of caution and anticipate high distal exposure. Dissection flaps that extend into the intracranial carotid should give pause and the involvement of neurosurgeons in the preoperative period is warranted. Fortunately, as the carotid aneurysm grows the ICA can elongate and become more redundant. Extreme tortuosity of the carotid is a relative contraindication to endovascular repair; moreover, the additional carotid length lends to direct carotid–carotid reconstruction or a hybrid approach to reconstruction.
External carotid artery disease: Attention to the proximal ECA is warranted as the proximal ECA can be used for inflow during an ICA to ECA transposition.
Contralateral disease: As mentioned previously, contralateral ICA occlusion increases the likelihood of cerebrovascular events during the ipsilateral clamp time. If there are concerns on duplex, CTA or MRA, angiography should be performed to estimate contralateral disease. For moderate- and high-grade disease and planned ipsilateral ligation, angiography and carotid balloon occlusion helps estimate the ability of the patient to tolerate ligation. Balloon occlusion can also be used to test ipsilateral clamping and measure back pressures. A back pressure greater than or equal to 50% of mean systemic pressure, or an absolute back pressure of 70 mm Hg, are considered safe.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
