Internal carotid artery dissection related to abnormalities of styloid process: is it only a matter of length?

Vascular Eagle syndrome, due to impingement of the extracranial internal carotid artery (ICA) by the styloid process (SP), is an uncommon and not yet widely recognized cause of ICA dissection. Up to now, this diagnosis is still presumptive, based mainly on the length of the SP. However, given the discrepancy between the much higher prevalence of an elongated SP in the population compared to the reported rate of Eagle syndrome, other anatomical factors beyond the length itself of this bony structure seem to be involved. We performed a retrospective single center case–control study of ICA dissection related to abnormalities of styloid process and age- and sex-matched controls affected by ICA dissection not related to abnormal relationship with the styloid process. In our work instead of considering SP length as the main criteria to differentiate the two groups, we decided to consider styloid process-internal carotid artery distance (at the dissection point) as the main factor to define a styloid process related dissection (SPRD). In fact in some patients, the distance between the dissected artery and the bony prominence was virtual. Our study showed that in patients with SPRD the styloid process angulation on the coronal plane tends to be more acute and that styloid process-C1 distance is significantly shorter at the side of the dissection. This data reinforces the idea that ICA dissection risk in the vascular Eagle syndrome has probably a multifactorial pathogenesis.