Midline Shift as a Predictor of Clinical and Radiological Outcomes Post-MMA Embolization

Background Chronic subdural hematoma (cSDH) is common in the elderly and often requires surgery due to significant morbidity, with recurrence rates of 2%‐37%. Middle meningeal artery (MMA) embolization is a promising minimally invasive alternative. Pre‐embolization midline shift (MLS), a key marker of cSDH severity, may predict clinical and radiological outcomes. Recognizing MLS as a prognostic factor can refine treatment strategies and improve patient outcomes. Methods We conducted a retrospective descriptive analysis of patients with cSDH who underwent MMA embolization at our community‐based Comprehensive Stroke Center between April 2019 and November 2024. Hematoma thickness and midline shift (MLS) were assessed on axial and coronal CT scans as the maximum thickness measured perpendicular to the brain surface, directed toward the skull's center. MLS was quantified by drawing a line connecting the most anterior and posterior points of the falx cerebri, then a perpendicular line from this axis to the septum pellucidum, with deviation recorded in millimeters. Results A total of 140 patients with cSDH were included, with 67% male and 33% female subjects, and a mean age of 74 years (range: 37‐97). Median pre‐procedural cSDH thickness and MLS were 15 mm and 7.5 mm (range: 0‐15 mm) Among them, 67% (n=94) had MLS <5 mm, while 33% (n=46) had MLS ≥5 mm. Pre‐procedural mRS distribution for MLS <5 mm was 0 in 30%, 1‐2 in 44%, and 3‐5 in 26%, whereas for MLS ≥5 mm, it was 0 in 20%, 1‐2 in 67%, and 3‐5 in 13%. Baseline cSDH thickness for MLS <5 mm was 0‐10 mm in 45%, 11‐20 mm in 49%, and >20 mm in 6%, while for MLS ≥5 mm, it was 0‐10 mm in 15%, 11‐20 mm in 70%, and >20 mm in 15%. Treatment strategies included standalone embolization (59%), embolization following prior surgical failure (6%), and embolization with concurrent surgical evacuation (35%). Unilateral embolization was performed in 47%, while 53% underwent bilateral embolization, with a 100% technical success rate. Post‐procedural median MLS was reduced to 5.5 mm (range: 0‐11 mm). The median cSDH thickness for patients with MLS <5 mm was 9 mm at 24 hours, 7 mm at 2 weeks, 5 mm at 6 weeks, 4.5 mm at 90 days, and 4 mm at last follow‐up. Contrastingly, for those with MLS ≥5 mm, median thickness was 14 mm at 24 hours, 13 mm at 2 weeks, 9 mm at 6 weeks, 6 mm at 90 days, and 5 mm at last follow‐up. Final mRS outcomes in the MLS <5 mm group were: 0 in 27%, 1‐2 in 39%, and 3‐5 in 34%. For the MLS ≥5 mm group, final mRS was 0 in 20%, 1‐2 in 60%, and 3‐5 in 20%. Conclusion Our findings suggest that pre‐embolization MLS is a key predictor of post‐procedural clinical and radiological outcomes, with greater MLS correlating with a slower reduction in cSDH thickness and varied functional recovery. However, a large‐scale randomized controlled trial is needed to validate our preliminary findings.