IntroductionStroke is one of the leading causes of death and disability in western societies and a prevalent public health concern worldwide [1]. Extracranial carotid artery stenosis due to atherosclerotic plaque burden is one of the major risk factors of forthcoming stroke [2]. Epidemiologic data document that ischemic stroke attributable to a diseased carotid artery corresponds with up to 18 % of all incidents leading to neurological events [3,4]. Furthermore, the prevalence of a cervical internal carotid artery stenosis increases with age and can be found in 6.9 % of the elderly population (> 65 years) [5]. Large randomized clinical trials (the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the European Carotid Surgery Trial (ECST)) have provided clear evidence of the usefulness of surgical treatment of patients with neurological symptoms for a degree of stenosis > 50 % in NAS-CET and > 70 % in ECST [6,7]. In contrast, the benefi t of carotid endarterectomy (CEA) for asymptomatic patients is less clear. Large multicenter randomized studies for asymptomatic carotid artery disease (the Asymptomatic Carotid Surgery Trial (ACST) and the Asymptomatic Carotid Atherosclerosis Study (ACAS)) demonstrated a small reduction in secondary stroke risk using CEA compared to medical treatment [8,9]. However, the absolute risk reduction was rather small [10,11].Epidemiological studies have already revealed that aging and sex are independent risk factors for cardiovascular disease [12,13]. However, the question as to how far potential changes in carotid plaque morphology might contribute to ischemic stroke during aging, especially due to unstable atherosclerotic lesions, has not yet been elucidated. Interestingly, very few studies have focused so far on lesion morphology and instability as a function of age, sex, or patient symptomatology [14 -20]. The data suggest that especially neurological symptoms are often caused by critical changes in carotid plaque morphology, leading to lesion instability. Consequently, unfavorable alterations in the pathophysiology of atherosclerotic plaques in asymptomatic patients might cause an increased risk of stroke.The aim of the current study was therefore to analyze plaque instability as a function of age and sex in patients with asymptomatic carotid artery stenosis by means of his- 2004 -2013) at the Munich Vascular Biobank were analyzed. Ascertainment of lesion stability/instability was performed on formalin-fi xed paraffi n-embedded tissue samples using hematoxylin-eosin and elastic van Gieson staining. Unstable plaques were considered lesions with a fi brous cap < 200 μm overlaying lipid-rich atheroma. Results: The average age of the patients was 69.3 ± 8.2 years. Independent of age, asymptomatic men had in total more frequently unstable plaques in contrast to women (41 % versus 52%, p = 0.042). No differences were found in plaque instability between age-related quartiles (< 65, 65-69, 70 -74, > 74 years) for female sex (p = 0.422). In men, a continuous increase ...