Association of Inner Membrane Visibility on Noncontrast CT With Response to Middle Meningeal Artery Embolization in Chronic Subdural Hematoma

<h3>BACKGROUND AND PURPOSE:</h3> Chronic subdural hematoma (CSDH) is characterized by inflammatory and angiogenic membrane formation. Although middle meningeal artery embolization (MMAE) targets this vascular supply and reduces recurrence, insufficient hematoma regression occurs in some patients. We hypothesized that inner membrane visibility on noncontrast CT (NCCT), a potential marker of membrane characteristics, is associated with response to MMAE in CSDH. <h3>MATERIAL AND METHODS:</h3> We retrospectively reviewed patients with CSDH who underwent MMAE at two institutions between July 2019 and November 2024. Inner membrane visibility on NCCT was graded as none (0%), partial (&gt;0% to &lt;90%), or complete (≥90%). The primary outcome was hematoma non-response, defined as rescue surgery or relative hematoma volume ≥90% at 3 months. Secondary imaging outcomes included 3-month absolute and relative hematoma volumes across NCCT inner membrane visibility categories. <h3>RESULTS:</h3> Forty-five patients comprising 56 treated hemispheres were included. NCCT inner membrane visibility was classified as none in 16 hemispheres, partial in 33, and complete in 7. Interrater agreement for NCCT grading was substantial (κ=0.64), and agreement between NCCT- and immediate post-MMAE CT-based classifications was almost perfect (κ=0.81). Binary classification of complete versus non-complete visibility also showed almost perfect agreement between NCCT and immediate post-MMAE CT (κ=0.84). At 3 months, both absolute and relative hematoma volumes increased stepwise from none to partial to complete visibility (both P&lt;.001). Hematoma non-response was significantly more frequent in hemispheres with complete NCCT inner membrane visibility than in those with non-complete visibility (57.1% vs 6.1%; P=.003). In an exploratory Firth-penalized logistic regression model adjusting for baseline hematoma volume and Embosphere size, complete visibility was associated with hematoma non-response (adjusted OR, 17.37; 95% CI, 2.36–224.88; P = .005). <h3>CONCLUSION:</h3> Complete inner membrane visibility on baseline NCCT was associated with hematoma non-response after MMAE in this small exploratory cohort. This hypothesis-generating finding requires validation in larger independent cohorts.