EICAA, while uncommon, poses considerable risks necessitating a proactive therapeutic approach
Extracranial internal carotid artery aneurysms (EICAs) are infrequently encountered pathological entities, constituting less than 1% of all aneurysms and approximately 0.4% of peripheral aneurysms[1, 2]. The etiology of EICAs remains subject to debate, with proposed associations including atherosclerosis, trauma, surgical history, infection, radiation exposure, and connective tissue diseases, such as Marfan syndrome[2, 9]. While EICAs seldom rupture, they commonly manifest as pulsatile masses or present with focal symptoms related to adjacent structures[2]. Notably, infarction or transient ischemic attacks (TIAs) may ensue due to thromboembolism from intra-aneurysmal thrombus or a floating thrombus within a narrow neck remnant[2]. The case under consideration presented with dysphagia attributed to cranial nerves IX-XII involvement from aneurysm mass effect and TIA symptoms stemming from acute thromboembolism formation within the aneurysm.
Surgical excision with in-situ anastomosis stands as the gold standard, yet is not applicable to massive aneurysms located in the high cervical segment near the skull base.
The absence of unified treatment guidelines for EICAs underscores their rarity. Nonetheless, surgical intervention is generally regarded as the preferred option, encompassing approaches such as simple carotid ligation, aneurysm repair, aneurysm resection with anastomosis/vascular reconstruction, and endovascular treatment[10, 11]. Historical perspectives reveal the evolution of treatment methodologies. The initial utilization of carotid ligation by Professor Cooper in 1805[12], though associated with substantial risks and high stroke incidence, persisted until the mid-20th century[12]. With advancements in surgical and endovascular techniques, carotid occlusion has yielded to aneurysm resection and blood flow reconstruction[2], with carotid ligation reserved for exceptional cases [13].
Open surgical repair remains the contemporary gold standard for EICAs[11], encompassing aneurysm resection with end-to-end anastomosis, aneurysm repair, and patch angioplasty. Pioneering procedures by Professors Dimtza and Beall in the 1950s and 1960s laid the foundation for addressing extracranial internal carotid aneurysms[14, 15]. However, challenges arise in treating high cervical segment aneurysms near the skull base[16], necessitating lateral skull base techniques[17, 18]. In 1978, Professor Fisch introduced the infratemporal fossa approach, maximizing exposure but at the expense of potential complications, including hearing loss and neurologic damage[10, 17, 19–21]. Despite these drawbacks, open surgical repair remains the prevailing standard for EICAs [11].
Endovascular Intervention: Selective Yet Risk-Laden
Advancements in endovascular techniques have expanded treatment options for EICAs, particularly those in high cervical segments. Endovascular methods, including covered stents, stent-assisted embolization, and flow-diverting devices[22–24], offer alternatives to open surgery, particularly in cases where conventional exposure is challenging [10]. However, the limitations of endovascular treatment are evident, with reported risks of stroke, aneurysm rupture, and vascular injury [25]. Factors such as unclear aneurysm neck display and large size pose challenges[23], underscoring the need for selective application of endovascular intervention.
Cerebrovascular Bypass: Advantages and Considerations
Cerebrovascular bypass emerges as a favorable option for EICAs, particularly in cases where open surgery or endovascular intervention presents challenges. High cervical segment aneurysms carry inherent risks, including unpredictable embolism, distal control difficulty, peripheral structure injury, and cranial nerve damage [11]. To address these concerns, high-flow bypass techniques, such as carotid-radial/ saphenous vein-middle cerebral artery bypass, offer a promising avenue for restoring normal blood flow and isolating the aneurysm[26–28].
However, when dealing with high cervical aneurysms, particularly those situated below the petrous segment of the internal carotid artery, the recipient vessel for bypass surgery is often found at challenging depths, either at ICA-C7 or MCA-M2. This poses difficulties in access, and the bypass method employed cannot entirely isolate the affected internal carotid artery, leaving a residual risk of thrombus embolism. Temporary occlusion of the internal carotid artery or middle cerebral artery during surgery may significantly impact patients sensitive to ischemia[27]. The primary objective, therefore, is to maximize the restoration of antegrade blood flow without the necessity of opening the skull.
In 1980, Fisch et al. introduced a pioneering method for reaching the high cervical and petrous segments of the internal carotid artery through a "subtotal petrosectomy" combined with cervical exposure. This method revolutionized the exposure of the petrous segment of the internal carotid artery[17, 18]. Subsequently, many surgeons have endeavored to repair and bypass the cervical and petrous segments of the internal carotid artery using this approach, achieving favorable therapeutic outcomes[29, 30]. Despite not requiring skull opening, the primary risk associated with exposing the petrous segment involves potential hearing loss and damage to cranial nerve function[10]. It has been reported that there is a 20–23% incidence of temporary cranial nerve palsy after surgery [31], with almost all patients experiencing temporary facial paralysis. Other drawbacks include impaired ear function and chorda tympani nerve damage[10]. These complications are linked to petrous bone removal, facial nerve displacement, and condyle process exposure, with no substantial advantage apparent in utilizing this approach.
In contrast to the aforementioned procedure, Miyazaki et al. exposed the petrous segment of the internal carotid artery through resection of the middle skull base, enabling bridge surgery based on this exposure [32, 33]. Fitzpatrick et al. subsequently standardized and improved this bridge method[34]. Building upon the detailed anatomical insights provided by Glassock[29] and Sekhar[30], Fitzpatrick devised a modified bypass technique requiring minimal resection of the temporal bone at the middle skull base, eliminating the need for extensive petrous bone removal or facial nerve displacement. This approach allows for the horizontal exposure of approximately 1cm of the petrous segment of the internal carotid artery, sufficient for subsequent bypass surgery. In our approach, we utilized this exposure method to horizontally expose the petrous segment of the internal carotid artery as the recipient vessel, with the ipsilateral external carotid artery serving as the donor vessel. The radial artery was connected to them through a subcutaneous tunnel and subsequently anastomosed. By completely isolating the affected segment of the internal carotid artery, this process involved only one temporary occlusion of the internal carotid artery, further diminishing the potential risk of ischemia. The feasibility of such bypasses is contingent upon meticulous surgical planning and consideration of individual patient characteristics.