Bilateral Carotid Artery Dissection Due to Asymmetric Styloid Processes: A Rare Case Report Highlighting the Role of Anatomical Factors Beyond Length

Elongation of the styloid process (SP) is a recognized etiologic factor in vascular pathologies such as carotid artery dissection (CAD), particularly in Eagle syndrome or stylocarotid artery syndrome. However, CAD involving an SP of normal length is exceedingly rare and often overlooked in clinical evaluations. We present a unique case of bilateral CAD caused by mechanical injury from asymmetric SPs - one elongated and the other of normal length - challenging the conventional belief that only elongated SPs carry clinical importance. A 47-year-old female patient experienced sequential episodes of bilateral CAD over a seven-month period. Radiological evaluations identified bilateral CAD likely attributed to the left SP of normal length (22 mm) and the right SP with elongation (35 mm). Both SPs were located in close proximity (<1 mm) to their respective internal carotid arteries (ICAs). Notably, despite its normal length, the left SP had a steep medial angulation of 65.1°, contributing to the ICA impingement. To restore vascular patency and prevent recurrence, the patient underwent successful bilateral carotid artery stenting followed by transcervical styloidectomies. While elongated SPs are commonly implicated in unilateral vascular symptoms, bilateral CAD related to SP impingement is rare. This case illustrates that even an SP of normal length can cause vascular injury when it exhibits atypical angulation and lies in close proximity to the ICA. Contrary to the conventional belief that only SP elongation has clinical importance, SPs of normal length may play a pathogenic role in SP-related CAD under specific anatomical conditions. We emphasize the importance of a comprehensive radiological evaluation that focuses not solely on SP length when considering potential SP-related vascular pathology.