OBJECTIVE: To determine the natural history of dissecting aneurysm (DA) and 
whether DA is associated with an increased recurrent stroke risk and whether 
type of antithrombotic drugs (antiplatelets vs anticoagulants) modifies the 
persistence or development of DA.
METHODS: We included 264 patients with extracranial cervical artery dissection 
(CAD) from the Cervical Artery Dissection in Stroke Study (CADISS), a 
multicenter prospective study that compared antiplatelet with anticoagulation 
therapy. Logistic regression was used to estimate age- and sex-adjusted odds 
ratios. We conducted a systematic review of published studies assessing the 
natural history of DA and stroke risk in patients with non-surgically-treated 
extracranial CAD with DA.
RESULTS: In CADISS, DA was present in 24 of 264 patients at baseline. In 36 of 
248 patients with follow-up neuroimaging at 3 months, 12 of the 24 baseline DAs 
persisted, and 24 new DA had developed. There was no association between 
treatment allocation (antiplatelets vs anticoagulants) and whether DA at 
baseline persisted at follow-up or whether new DA developed. During 12 months of 
follow-up, stroke occurred in 1 of 48 patients with DA and in 7 of 216 patients 
without DA (age- and sex-adjusted odds ratio 0.84; 95% confidence interval 
0.10-7.31; p = 0.88). Published studies, mainly retrospective, showed a 
similarly low risk of stroke and no evidence of an increased stroke rate in 
patients with DA.
CONCLUSIONS: The results of CADISS provide evidence suggesting that DAs may have 
benign prognosis and therefore medical treatment should be considered.