Anatomical characteristics of the styloid process associated with internal carotid artery dissection: a systematic review and meta-analysis of controlled trials.

Purpose Internal carotid artery dissection (ICA-D) is an important cause of stroke in adults. The styloid process (SP) may be associated with ICA-D due to potential (micro)trauma resulting from its close anatomical proximity to the internal carotid artery (ICA). The aim of this systematic review with meta-analysis is to investigate the association between SP characteristics -particularly SP-ICA distance - and ICA-D.Methods A systematic review was conducted across six databases to identify observational studies comparing ICA-D patients to controls. The primary outcome of interest was the association between SP-ICA distance and ICA-D. Secondary outcomes included associations between ICA-D and the SP length or angulation. A random-effects meta-analysis was performed, including a subgroup analysis of moderate/high-quality studies. Effect sizes were expressed as standardized mean differences (SMD, Hedges' g).Results Six studies were included in the systematic review, of which five were eligible in the meta-analysis. The pooled analysis of all five case-control studies (270 ICA-D patients and 377 controls) showed no significant difference in SP-ICA distance (SMD = -0.92, p = 0.143); with a high degree of heterogeneity (I2 = 98%). Subgroup analysis of moderate/high-quality studies evaluating the SP-ICA distance ipsilateral to the ICA-D (4 studies) yielded a negative pooled SMD (-0.29, p = 0.047; moderate heterogeneity: I2 = 64%), consistent with a shorter SP-ICA distance in ICA-D cases. Meta-analysis of the SP length (3 studies) found no significant association (SMD 0.24, p = 0.139) and two studies also found no significant relationship between ICA-D and SP angulation.Conclusion A shorter SP-ICA distance was associated with ICA-D, whereas no significant associations were observed for SP length or angulation. However, the available evidence remains limited and heterogeneous.Systematic Review Registration CRD42024582594.