Aggravation of rainbow sign on hematoma membrane by arterial spin labeling predicts chronic subdural hematoma recurrence following middle meningeal artery embolization

Background Recurrence remains a critical challenge in patients with chronic subdural hematoma (CSDH) treated with middle meningeal artery embolization (MMAE), yet the underlying mechanisms and reliable predictors of this phenomenon remain poorly understood. Current predictors of recurrence rely on invasive or radiation-based techniques, prompting the need for non-invasive imaging markers. This study aimed to evaluate the ‘rainbow sign aggravation’ by arterial spin labeling (ASL) on the hematoma membrane as a predictor of CSDH recurrence after MMAE. Methods We retrospectively studied ASL scans from 100 patients with CSDH who underwent MMAE between October 2022 and March 2025. The rainbow sign was defined as the hyperperfusion on the outer hematoma membrane. Inter-rater reliability, univariate analyses, and logistic regression were used to assess associations between the rainbow sign and recurrence. Results In the 100 patients who underwent MMAE, the pre-embolization rainbow sign was identified in 29 (29.0%) cases while the post-embolization rainbow sign was observed in eight (8.0%). Post-embolization rainbow sign and rainbow sign aggravation were significantly correlated with recurrence (P<0.001 for both), while no recurrence occurred in patients with a resolved rainbow sign. Subgroup analysis showed that rainbow sign aggravation was correlated with persistent headache (χ²=32.683, P<0.001), motor strength weakness (χ²=51.981, P<0.001), and worse neurological outcomes (χ²=33.076, P<0.001). Conclusion The dynamic changes in the rainbow sign following MMAE correlated with the treatment response, with rainbow sign aggravation a significant predictor of hematoma recurrence. Integrating this marker into clinical assessments might enable personalized treatment strategies to reduce recurrence and improve outcomes in patients with CSDH.