Morphological changes in chronic subdural hematomas following upfront middle meningeal artery embolization: sequence, timing, and association with outcomes

OBJECTIVE Middle meningeal artery embolization (MMAE) is an increasingly utilized approach for the treatment of chronic subdural hematomas (CSDHs). The course of morphological progression of CSDHs following MMAE is poorly understood. Herein, the authors aimed to describe these morphological changes and assess their prognostic significance for the outcomes on follow-up. METHODS A single-institution retrospective cohort study of CSDH cases treated by upfront MMAE, without prior or adjunctive surgical evacuation, was performed. Clinical outcomes, complications, and the need for rescue surgery on follow-up were recorded. Hematomas were categorized into 6 morphological subtypes. All baseline and follow-up head CT scans were assessed for CSDH structural appearance, density, and loculation. Changes in CSDH size were quantified via 3D reconstruction for volumetric measurement. RESULTS Overall, 52 CSDHs in 45 patients treated with upfront MMAE were identified. Hematomas were followed for a mean of 92.9 days. Volume decreased by ≥ 50% in 79.6% of the CSDHs. The overall rescue surgery rate was 9.6%. A sequence of morphological changes after MMAE was identified. Hematomas that diverged from this sequence (5.4%) all progressed toward treatment failure and required rescue surgery. The CSDHs were categorized into early, intermediate, and late stages based on the baseline morphological appearance. Progression from early to intermediate and then to late stage took 12.7 and 30.0 days, respectively, on average. The volume of early/intermediate- and late-stage hematomas decreased by ≥ 50%, a mean of 78.2 and 47.6 days after MMAE, respectively. Early- and intermediate-stage hematomas showed a trend toward more favorable outcomes compared with late-stage hematomas. The density of homogeneous hypodense hematomas (HSDHs) transiently increased immediately after MMAE (p < 0.001). A marked decrease in density and volume 1 to 3 weeks after MMAE in HSDHs was detected, the lack of which indicated an eventual need for rescue surgery. In HSDHs, a baseline mean density of < 20 HU, and a lower density than baseline by 1 month post-MMAE were predictors of favorable outcomes. The baseline hematoma volume, axial thickness, midline shift, and loculation were not correlated with MMAE outcomes. Loculated, trabecular, and laminar hematomas, which are known to have unfavorable surgical outcomes, had MMAE outcomes similar to those of other "surgical" hematomas. CONCLUSIONS The current study was the first to describe the nature, sequence, and timing of morphological changes of CSDHs after MMAE treatment and has identified structural features that can predict treatment outcomes.