Middle meningeal artery embolization (MMAE) now has randomized evidence from five completed trials, with pooled analyses increasingly favoring benefit. Yet no trial, and no predictor identified to date, explains which patients fail treatment through a vascular mechanism. We propose that a subset of chronic subdural hematoma (CSDH) patients has clinically significant membrane supply from arteries beyond the MMA — the accessory meningeal, ascending pharyngeal, and occipital arteries — the same anastomotic network that makes multi-vessel assessment standard practice in dural arteriovenous fistula (DAVF) treatment planning. We review the anatomic basis for this network, direct evidence from DAVF literature linking multiple feeders to treatment failure, and gaps in how CSDH trials have characterized MMA anatomy. We propose a multi-vessel angiographic assessment protocol, adapted from DAVF practice, to identify this subset prospectively.