Onyx dilution reduces time to resolution of chronic subdural hematomas after middle meningeal artery embolization.

Background: The benefit of distal embolite penetration for middle meningeal artery (MMA) embolization in chronic subdural hematomas (cSDH) remains controversial.

Objective: To compare the use of diluted Onyx with undiluted Onyx in the management of cSDH.

Methods: This is a retrospective study of patients with cSDH who underwent MMA embolization using Onyx 18 at our institution. The study population was divided into two subgroups based on whether the Onyx used was diluted or not. Baseline characteristics and technical aspects were compared. Primary outcome was cSDH resolution at follow-up. Secondary outcomes included time to resolution and duration of procedure. Univariate statistical analysis was performed.

Results: Of the 111 MMA embolizations performed at our institution, 99 were performed using Onyx 18 only. Within this cohort, 53 (53.5%) cases used standard Onyx and 46 (46.5%) cases used diluted Onyx. The diluted Onyx group had significantly greater volume of embolic agent used measured radiographically (P<0.001). There was no significant difference in duration of procedure. The percentage of cSDH resolution at last follow-up was similar between the two groups (P=0.98), but the time to resolution was significantly shorter in the diluted Onyx group (P=0.02).

Conclusion: The use of diluted Onyx for MMA embolization is associated with greater embolization volume achieved under similar procedural times. While the percentage of patients who achieved cSDH resolution with diluted Onyx is similar to that for standard Onyx, the time to cSDH resolution is significantly shorter. Adoption of Onyx dilution can be considered in MMA embolization for cSDH.