Cervical carotid artery dissection is associated with styloid process length

OBJECTIVE: To investigate whether cervical carotid artery dissection (CCAD) is associated with anatomic characteristics of the styloid process of the temporal bone. METHODS: CT angiograms from 38 case patients with CCAD and 38 age- and sex-matched control subjects without dissection were studied. Styloid process length, angulation in the axial and rostral-caudal planes, and proximity to the carotid artery were measured bilaterally by raters blinded to radiology reports and clinical information. RESULTS: In control subjects, there was substantial variation in styloid process length (range 4.6-42.9 mm), medial angulation (range 16-89°), caudal angulation (range 31-80°), and proximity to the carotid (range 0.7-15.4 mm). Control subjects also demonstrated marked symmetry between sides (correlation coefficients 0.80 for length, 0.34 for proximity, 0.81 for medial angulation, and 0.87 for caudal angulation). In case patients, the mean styloid length on the side of the dissection was not significantly longer than that on the contralateral side (mean 30.3 vs 29.7 mm, p = 0.30). The styloid process was significantly longer ipsilateral to the dissection in case patients compared with the side-matched process in control subjects (mean 30.3 vs 26.6 mm, p = 0.03). Carotid dissection was associated with increasing styloid process length (OR OR 1.08/mm, 95% confidence interval CI 1.002-1.17, p = 0.04). The OR of dissection in the highest quartile of length compared with that in the lower 3 quartiles was 4.0 (95% CI 1.3-14.2, p = 0.03). CONCLUSIONS: CCAD is associated with a longer styloid process, suggesting that mechanical injury from the styloid may contribute to the pathogenesis of CCAD.