Aneurysms of the extracranial carotid artery

Abstract

Extracranial aneurysms of the carotid artery (ECAA) are rare, but the exact incidence is unclear. ECAAs appear to be mostly coincidental findings but can lead to significant morbidity. Cerebral ischemia due to embolism from the aneurysm is the most feared symptom. Dissection and degeneration are two distinct underlying mechanisms in ECAA formation. Computed tomography angiography is the most commonly used modality for diagnostics and follow-up in ECAA. Aneurysm size or growth can be assessed through measurement of the maximum aneurysm diameter or the aneurysm volume. Volume measurement is feasible in ECAA, although the intra-observer and inter-observer reliability of diameter measurements are superior. Theoretically, volumetric measurements better assess aneurysm morphology than diameter measurements and are more sensitive for detection of aneurysm growth and therefore they could be added to diameter measurements in assessing aneurysm growth. No evidence-based guidelines or indications for invasive therapy in ECAA are available. Presumably, the natural course of ECAAs is poor, with a reported stroke rate of up to 50%. However, we found a stroke and mortality rate of 5% in conservative management of ECAA, and all patients with small, stable and asymptomatic ECAA had a favorable outcome. Traditional surgical treatment, which is the current treatment of choice of a symptomatic or growing ECAA, consists of open resection of the entire aneurysm, with or without arterial replacement with an interposition graft. In case of an elongated or redundant carotid artery, a primary end-to-end reconstruction can be made with a single anastomosis. Otherwise, an autogenous saphenous vein is the graft of choice to create an interposition bypass of the resected artery. When no suitable vein is available, a polytetrafluoroethylene or Dacron interposition graft can be used. Early and long-term mortality and the number of strokes are low in surgical treatment, which supports the assumption that invasive treatment can prevent stroke. However, this surgical approach has been associated with the risk of stroke and cranial nerve injury. Endovascular stent placement could be a good alternative, especially in ECAAs located distal in the internal carotid artery or in patients unfit for surgery. Although the long-term outcome of endovascular therapy is still unknown, the periprocedural and short-term results reported in the literature are promising. Stents covered with an internal or external lining are predominantly applied to exclude the aneurysm from the circulation. Exclusion of an aneurysm is also possible with a bare-metal stent. The advantage of a bare-metal stent is the superior flexibility, which is very useful in the often-tortuous carotid arteries. For a proper assessment of the benefit and complication risk from the different treatment and revascularization options for ECAA, a better insight in vascular procedural outcome is needed and especially in the natural follow-up. Given the limited number of patients, randomized controlled trials are infeasible in rare diseases such as ECAA. To collect data on ECAAs we designed the Carotid Aneurysm Registry (CAR), a prospective Web-based international registry assessing natural course, results of intervention, and follow-up data in patients with an ECAA.