BackgroundNon-ischemic cerebral enhancing (NICE) lesions following aneurysm endovascular therapy are exceptionally rare, with unknown longitudinal evolution.ObjectiveTo evaluate the radiological behavior of individual NICE lesions over time.MethodsPatients included in a retrospective national multicentric inception cohort were analyzed. NICE lesions were defined, using MRI, as delayed onset punctate, nodular, or annular foci enhancements with peri-lesion edema, distributed in the vascular territory of the aneurysm treatment, with no other confounding disease. Lesion burden and the longitudinal behavior of individual lesions were assessed.ResultsTwenty-two patients were included, with a median initial lesion burden of 36 (IQR 17–54) on the first MRI scan. Of the 22 patients with at least one follow-up MRI scan, 16 (73%) had new lesions occurring mainly within the first 200 weeks after the date of the procedure. The median number of new lesions per MRI was 6 (IQR 2–16). Among the same 22 patients, 7 (32%) had recurrent lesions. The median persistent enhancement of a NICE lesion was 13 weeks (IQR 6–30). No factor was predictive of early regression of enhancement activity with lesion regression kinetics mainly being patient-dependent.ConclusionsThe behavior of individual NICE lesions was found to be highly variable with an overall patient-dependent regression velocity.