When anatomy becomes pathology: Rethinking carotid-hyoid contact in cerebrovascular events

Abstract

In this letter, we comment on the recent article by Karangeli et al, which systematically examined the spatial relationship between the hyoid bone and the carotid arteries using computed tomography angiography. The authors revealed significant anatomical variability in the 224 patients in their study, with type VI (external carotid artery lateral to the hyoid) and type VIII (both carotid arteries lateral to the hyoid) being the most common non-null configurations. Notably, sex-based differences were identified, suggesting possible morphometric or biomechanical influences. These findings have important implications for radiologists and surgeons, as non-null variants - particularly types VIII and XI - might predispose to dynamic carotid compression, transient ischemic events, or intraoperative vascular injury. Recognizing these patterns during preoperative imaging can enhance surgical safety and improve the diagnostic evaluation of unexplained cerebrovascular symptoms. The study by Karangeli et al underscores the clinical importance of translating detailed anatomical mapping into preventive strategies that bridge imaging precision and vascular protection.

Key Words: External carotid artery; Internal carotid artery; Hyoid bone; Anatomy; Variation

Core Tip: This letter highlights the clinical importance of recognizing carotid–hyoid spatial variants identified by Karangeli et al. Their computed tomography angiography-based mapping demonstrates that non-null configurations - especially types VIII and XI - are more common than previously reported and may predispose patients to dynamic carotid compression, unexplained cerebrovascular symptoms, or intraoperative vascular injury. Incorporating carotid-hyoid assessment into routine imaging can improve diagnostic accuracy and enhance surgical safety.

TO THE EDITOR

The vascular anatomy of the head and neck is highly complex and variable, and it is essential to accurately characterize the spatial relationships between the vessels and adjacent bony structures in order to identify high-risk patients and guide appropriate surgical planning. The common carotid artery typically bifurcates at the C3-C4 vertebral level, giving rise to the internal carotid arteries (ICA) and external carotid arteries (ECA). However, several studies have shown that the carotid bifurcation level varies considerably among individuals, ranging superiorly to the level of the hyoid bone or styloid process (SP) and inferiorly to below the cricoid cartilage (C5-C6)[1]. This variability suggests the presence of a potentially important topographic relationship between the carotid arteries and the hyoid bone. Previous reports have indicated that aberrant carotid arterial courses not only are relevant to cerebral perfusion but may also contribute to mechanically induced atherosclerotic progression, transient ischemic attacks (TIAs), or even stroke. They represent a potential source of major vascular injury during neck surgery. However, despite extensive research on carotid branching patterns, the spatial configuration between the carotid arteries and the hyoid bone has received comparatively limited attention, creating a meaningful gap in both diagnostic and surgical practice[2,3].

Against this background of anatomical uncertainty, the recent study by Karangeli et al[4] in the World Journal of Radiology is particularly noteworthy. The authors used cervical computed tomography angiography (CTA) and systematically characterized the spatial relationship between the hyoid bone and the carotid arterial system in 448 heminecks from 224 patients. Through their incorporation of a relatively large sample and the use of multiplanar reconstructions together with three-dimensional volume rendering, their investigation provides one of the first precise evaluations of a long-neglected yet clinically relevant question: Which seemingly normal anatomical variants may, under specific conditions, serve as occult contributors to dynamic vascular injury or even precipitate distinct pathological states?

Building on this methodological strength, the findings of Karangeli et al[4] reveal that carotid-hyoid contact is far more prevalent than previously appreciated. The authors applied the CTA-based radiologic classification proposed by Manta et al[3] in 2023, which describes the position of the carotid arterial branches (common carotid artery, ICA, and ECA) relative to the greater horn of the hyoid bone and categorizes these relationships into 12 distinct types - the most comprehensive and systematic framework currently available. In their study, the authors demonstrated that 53.1% of patients exhibited some degree of spatial proximity or contact between the carotid arteries and the hyoid bone. The most frequent non-null configuration was type VI (the ECA lateral to the hyoid; 23.9%), followed by types VIII (both ICA and ECA lateral; 13.2%) and IX (the ICA medial to the hyoid; 10%). Rare variants, such as types XI (1.1%) and type XII (0.4%), were also identified, whereas types II, III, V, and VII were absent. Collectively, these observations demonstrate that the carotid-hyoid spatial relationship is more complex than previously described and that different configurations may carry distinct clinical implications. Notably, the distribution of contact types differed substantially from the frequencies reported in the original Manta et al[3] cohort (for example, type VIII occurred more than three times as often), underscoring the influence of ethnic, morphometric, or biomechanical factors and emphasizing the need for regionally representative anatomical datasets.

ASSOCIATION BETWEEN DEMOGRAPHIC VARIABLES AND CAROTID-HYOID CONTACT

Furthermore, the study contributes a novel dimension by revealing sex-related anatomical differences. In related work, Karangeli et al[4] demonstrated that men have a significantly longer hyoid bone than women. Congruently, Fakhry et al[5] reported higher values of greater horn length in male participants, whereas greater horn angle was increased in female participants. The cohort studied by Karangeli et al[4] revealed that greater horn length was likewise greater in men; however, sex was not significantly associated with greater horn angle. The hyoid bone exhibits highly variable morphological characteristics that are closely associated with individual differences in terms of sex, height, and body weight[6]. A growing body of literature supports the notion that the hyoid bone displays marked sexual dimorphism. Abdelkader et al[6] employed machine-learning techniques in an Egyptian cohort and further demonstrated significantly larger hyoid bone in male than in female participants, with all measured dimensions being higher in men. The distribution of topographical types differed significantly between sexes (P = 0.012). Male patients were more likely to exhibit lateralized contact types, such as types VI, VIII, and IX, whereas female patients more frequently presented with type 0 and medialized configurations, including types IV, XI, and XII. In addition, among the 121 patients (54.02%) with bilateral symmetry, most of the symmetric type 0, type VI, type VIII, and type IX patterns were observed in males. Further, Abdelkader et al[6] investigated sex-related differences in their cohort and revealed no substantial variation between men and women in the distribution of carotid-hyoid relationship types. Type VI was the most frequently observed configuration in both sexes within their bilateral carotid-hyoid classification scheme. These findings suggest that differences in suprahyoid muscular tension, cervical biomechanical loading patterns, or hormone-related influences might modify the course of the carotid arteries, thereby contributing to sex-specific vascular risk profiles that have not been previously recognized.

Concerning age, isolated case reports have indicated that stroke in some young patients may be attributable to hyoid-related carotid artery injury[7]. However, to date, no systematic or population-based investigations of how carotid-hyoid anatomy varies across age groups or ethnicities have been conducted. Indirect insights can be drawn from studies of the SP. A previous study has shown that SP length increases during the third decade of life, with a further, smaller increment after 60 years of age. Similarly, Jung et al[8] showed that the upper percentiles of SP length increase with advancing age, particularly in men older than 35 years. These observations support the notion that SP elongation may have both congenital and acquired components, with a tendency toward progressive ossification over subsequent decades[9]. Comparable longitudinal and multiethnic population-based studies are also warranted for the hyoid bone.

CLINICAL SIGNIFICANCE OF CAROTID-HYOID ANATOMY

The clinical relevance of these anatomical findings becomes even more pronounced when they are considered alongside the published case literature. Although type VI was the most frequently observed non-null configuration, it has not been associated with clinical symptoms in any reported case. In contrast, several reports have documented strong associations between types VIII and XI and TIAs, recurrent focal neurologic deficits, carotid artery dissection, and formation of pseudoaneurysm[10,11]. A review of 20 published case reports further showed that these rare but “high-risk” configurations occur disproportionately in younger individuals who do not have conventional vascular risk factors, functioning as plausible culprits in recurrent TIAs or cryptogenic stroke[7,12]. This paradox reinforces a central concept: Anatomically uncommon carotid variants may possess disproportionately high pathogenic potential. The dynamic nature of the carotid-hyoid interface likely underlies this phenomenon. At rest, the carotid-hyoid anatomical relationship provides the fundamental spatial configuration for evaluating its clinical risk. This static geometry not only defines the interface through which mechanical forces are transmitted to the vessel but also serves as the geometric substrate for dynamic compression, thereby affecting the likelihood and severity of arterial impingement during swallowing or neck motion. Hence, the dynamic behavior of the carotid-hyoid interface may represent a key mechanistic association underlying the pathogenic potential of carotid anatomical variants.

Previous studies using dynamic ultrasonography and swallowing-motion imaging have shown that certain configurations - particularly types VIII and XI - can result in transient compression, displacement, or repetitive impingement of the ICA during swallowing, neck rotation, flexion-extension, or physical exertion[7,13]. The reports by Tokunaga et al[14] and Hong et al[15] further substantiate this mechanism, demonstrating pronounced ICA-hyoid contact during swallowing and golf swing-related cervical motion, respectively. A recent ultrasound study described the dynamic displacement of the carotid artery during swallowing due to hyoid interference - specifically, a shift of the artery from the lateral to the medial side of the hyoid bone, where it remained for several seconds - as a “flip-flop phenomenon” and implicated it as a potential cause of carotid stenosis and stenosis-related stroke[16]. Such dynamic interactions may precipitate intimal disruption, dissection, microembolic release, or mechanically induced vascular remodeling - pathological changes that static CTA alone cannot adequately capture.

SURGICAL RELEVANCE OF THE CAROTID-HYOID RELATIONSHIP

From a surgical standpoint, these findings carry equally substantial implications. Medialized configurations (types I-V, IX, and XI) position the ICA dangerously close to the posterior pharyngeal wall, increasing the risk of catastrophic arterial injury during transoral procedures, such as tonsillectomy, abscess drainage, or oropharyngeal tumor resection. Conversely, lateralized configurations (types VI-X) pose challenges for transcervical approaches by restricting surgical exposure or increasing the risk of vascular traction. Mixed variants, including types XI and XII, compound these concerns by presenting risk profiles that are associated with both medial and lateral displacement. Carotid stenting is generally discouraged in the setting of significant stenosis in patients in whom plaque formation is associated with hyoid-induced carotid compression, because persistent external mechanical stress may predispose to in-stent restenosis. Instead, an acute management strategy that combines surgical revascularization with compressive structure resection is frequently regarded as a more appropriate option[17]. Accordingly, preoperative imaging should routinely incorporate carotid-hyoid topographic assessment to optimize surgical planning and mitigate preventable vascular injuries.

CONCLUSION

Taken together, these insights highlight clear priorities for future research. Larger, multicenter studies integrating sex-specific analyses, functional imaging modalities, and longitudinal follow-up are warranted to more accurately define the risk profiles of each topographical type. More broadly, the work of Karangeli et al[4] underscores that the carotid-hyoid relationship is far from an anatomical curiosity; rather, it represents a critical interface with direct implications for cerebrovascular health, surgical safety, and diagnostic precision. Radiologists should maintain heightened awareness of this anatomical relationship in patients with cryptogenic stroke, recurrent focal neurologic deficits, or unexplained cervical symptoms. Incorporating a carotid-hyoid topographic evaluation into routine CTA reporting not only enhances diagnostic completeness but also enables timely risk identification and meaningful prevention, ultimately bridging the gap between structural anatomy and clinical protection.