1331 Int. J. Morphol., 39(5):1331-1336, 2021. Effect of Internal Carotid Artery Aberrations on the Distance Between Styloid Process and Carotid Artery Efecto de las Variaciones de la Arteria Carótida Interna en la Distancia entre el Proceso Estiloides y la Arteria Carótida K. Esen1; Y. Balci 1 ; A. Ozgur 1 ; S. Erdogan 2 & B. Ten 1 ESEN, K.; BALCI, Y.; OZGUR, A.; ERDOGAN, S. & TEN, B. Effect of internal carotid artery aberrations on the distance between styloid process and carotid artery. Int. J. Morphol., 39(5):1331-1336, 2021. SUMMARY: The objective of this study was to evaluate the role of the variations of carotid artery course on the relationship between styloid process (SP) and internal carotid artery (ICA). Carotid CT angiography scans of 170 patients were retrospectively evaluated. The variability of the course of ICA were classified. The length and medial angulation of the SP were measured on coronal 3D images. On axial images, the shortest distance between the bone edge of the SP and ICA were measured. The distance between SP and ICA among the course patterns of carotid artery were compared statistically. In the comparison of distances between SP and ICA with respect to the course of ICA, the difference between straight and curving (p <0.001) was statistically significant. Curving caused the separation of ICA and SP. The highest and the shortest distance was at the curving and coiling group, respectively. We found that SP-ICA distance has a positive and negative correlation with SP angle (p<0.001) and SP length (p<0.001), respectively. The course of ICA is one of the major determinants affecting the relationship of ICA and SP. The curving pattern of ICA has a tendency to increase the distance between SP and ICA. KEY WORDS: Styloid process; Carotid artery; CT angiography; Aberration. INTRODUCTION Styloid process (SP), cornu minus of the hyoid bone and stylohyoid ligament form the stylohyoid complex (Basekim et al., 2005). Styloid process is a cartilaginous bone at the base of the temporal bone and a close relationship of SP with internal carotid artery (ICA) causes a clinically relevant condition. Calcification of stylohyoid complex and elongation of SP may give rise to Eagle syndrome which is generally divided into two common presentations called as classic Eagle syndrome and stylocarotid form (Sveinsson et al., 2013). The occurrence of symptoms is related with the distortion of adjacent anatomical structures by elongated SP. In the vascular or stylocarotid form of Eagle syndrome, SP is in contact with the extracranial segment of ICA (Sveinsson et al.). Impingement of internal or external carotid artery may cause pain along the distribution of the artery and headache or migraine by stimulation of the sympathetic nerve plexus associated with the artery (Chuang et al., 2007). Patients presenting with carotid dissections and neurological symptoms have been described (Faivre et al ., 2009; Sveinsson et al.; Aydin et al., 2018). Risk factors causing compression of carotid artery have been described in various studies. Elongation of SP, calcification of the stylohyoid complex, and narrowed SP angle are major factors for bony compression and the stylocarotid syndrome (Pokharel et al., 2013; Burulday et al., 2017; Eraslan et al., 2017). Variations of the course of carotid artery also have an important role on the relationship between ICA and SP. Getting closer of carotid artery with pharyngeal wall may lead hemorrhagic complications in surgical procedures of this region (Gossner et al., 2013). Therefore, various anatomical or angiographic studies have been reported to classify the variations of the course of carotid artery (Fazan et al., 2007; Gossner et al.; Zenteno et al., 2014). The classification described by Weibel & Fields is the most accepted one in the literature. Kinking, coiling and elongation are the main titles of course variations of carotid artery in this classification (Weibel & Fields, 1965a,b). It is well known that the prevalence increases with age (Gossner et al.). However, it is not clear whether the displacement of artery secondary to tortuosity decreases or increases the risk of ICA-SP contact. There are 1 Department of Radiology, Mersin University, Faculty of Medicine, Mersin, Turkey. 2 Department of Biostatistics and Medical Informatics, Mersin University, Faculty of Medicine, Mersin, Turkey.