Effects of Intradural Extension of Extracranial Cervical Artery Dissection on Outcomes: A Secondary Analysis From the STOP ‐ CAD Study

OBJECTIVE: Cervical artery dissection (CeAD) may be limited to the extracranial extradural space or extend to the intradural space. Intradural extension can potentially increase the risk of stroke and subarachnoid hemorrhage. However, the factors associated with intradural extension and its impact on clinical outcome remain unclear. METHODS: This was a secondary analysis of the STOP-CAD observational, multi-center study. Patients with CeAD and intradural extension (CeADid) were compared with those with pure CeAD extradural dissections (CeADed) using multiple regression analyses. RESULTS: Of 4,023 patients with CeAD, 534 (13.3%) had CeADid. In comparison to patients with CeADed, those with CeADid more often had clinical overt stroke or transient ischemic attack (TIA) at presentation, acute infarcts on imaging, a vertebral artery affected, and severe stenosis of the involved vessel (p < 0.001 for all). In contrast, carotid involvement and complete occlusions were more frequent in patients with CeADed (p < 0.001 for both). CeADid was associated with a shift in the distribution of scores on the modified Rankin Scale (mRS) toward worse functional outcome (odds ratio [OR] = 0.76, 95% confidence interval [CI] = 0.62-0.92) but the odds for favorable outcomes (mRS = 0-2) did not differ between the groups after appropriate adjustments on multivariate analysis. CeADid was independently associated with higher mortality at 180 days on multivariate analysis (adjusted OR = 2.84, 95% CI = 1.50-5.38). INTERPRETATION: CeADid is associated with more severe clinical presentation, a shift toward less favorable outcomes, and higher mortality rates. These findings suggest that CeADid may represent a high-risk type of CeAD. ANN NEUROL 2026;99:1189-1197.