Objective To analyze the changes of high-resolution magnetic resonance imaging (HR-MRI) characteristics in patients with spontaneous unruptured cervicocranial arterial dissection (CCAD) before and after drug treatment. Methods The data of 30 CCAD patients who were diagnosed in The First Affiliated Hospital of Naval Medical University (Second Military Medical University) from Aug. 2015 to Dec. 2022 and underwent HR-MRI before and after drug treatment were retrospectively and continuously collected. According to the improvement of the stenosis of dissecting vessels on magnetic resonance angiography (MRA) at follow-up, the patients were divided into improvement group (the patients who had a reduction of 1 grade or more in the lumen stenosis at follow-up compared with baseline) and unimprovement group (the patients who had an increase of 1 grade or more or no change in the lumen stenosis at follow-up compared with baseline). The differences in clinical data of patients in the improvement group and unimprovement group, as well as the lumen and wall characteristics of HR-MRI before and after treatment, were analyzed. Results A total of 30 dissections were found in the 30 CCAD patients, including 14 in the improvement group (11 completely returned to normal and 3 improved in the lumen stenosis) and 16 in the unimprovement group. The age of patients in the improvement group was significantly younger than that in the unimprovement group (［37.86±9.83］ years old vs ［56.94±9.86］ years old, P＝0.001), and there were no significant differences in other clinical characteristics (all P＞0.05). At baseline, in the improvement group the proportion of intramural hematoma was higher and the lumen stenosis was relatively mild, while in the unimprovement group the lumen stenosis was severe, and the intimal flap, double lumen sign and pseudolumen thrombosis were more common (all P＜0.05). At follow-up, intramural hematoma and the degree of lumen stenosis in the improvement group were significantly improved, while there were still many residual intramural hematoma, intimal flap, double lumen sign, and pseudolumen thrombus in the unimprovement group (all P＜0.05). At baseline, there was no significant difference in the enhancement of the dissection vessel wall between the 2 groups (P＞0.05). At follow-up, the enhancement of the dissection vessel wall in the improvement group was significantly decreased compared with the unimprovement group (P＜0.001). Conclusion HR-MRI can be used to evaluate the morphological changes of the lumen and wall of CCAD before and after drug treatment. Patients with younger age and relatively mild lumen stenosis at baseline can achieve better outcomes after drug treatment.