Hyperdense Capsule Sign at Noncontrast CT as an Indication for Middle Meningeal Artery Embolization for Nonacute Subdural Hematomas: A MAGIC-MT Trial Post Hoc Analysis.

Background Hematoma recurrence and progression remain common challenges in nonacute subdural hematomas (SDHs). The understanding of indications for middle meningeal artery embolization (MMAE) is limited. Purpose To investigate the utility of the hyperdense capsule sign (HDCS) at noncontrast CT for identifying potential candidates for MMAE for nonacute SDH. Materials and Methods In this post hoc analysis of the MAGIC-MT randomized controlled trial (September 2022 to December 2023) comparing adjunctive MMAE and usual care, participants were grouped by HDCS presence or absence at noncontrast CT. The primary outcome was symptomatic recurrence or progression of SDH. The Cochran-Mantel-Haenszel χ2 test, propensity score matching (PSM), multivariable analysis, and P value for interaction were used for subgroup comparisons. Results Among 697 participants included in this analysis (median age, 69 years [IQR, 61-74 years]; 575 male participants), 444 (63.7%) showed HDCS presence. Primary outcome incidence was lower in the embolization versus usual-care group among participants with the HDCS (5.0% vs 12.0%, P = .009; after PSM: 4.1% vs 11.2%, P = .04) but not among those without the HDCS (9.4% vs 5.6%, P = .24; after PSM: 10.3% vs 5.0%, P = .13), with an interaction between MMAE and HDCS presence (P = .01; after PSM: P = .01). The proportion of participants experiencing a serious adverse event was lower in the embolization versus usual-care group among those with the HDCS (5.9% vs 15.1%, P = .002; after PSM: 5.8% vs 15.5%, P = .02) but not among those without the HDCS (8.7% vs 5.6%, P = .34; after PSM: 9.4% vs 5.8%, P = .30), with a significant interaction (P = .01; after PSM: P = .02). Conclusion For participants with nonacute SDH, the presence of the HDCS was associated with a lower rate of recurrence or progression among those who underwent MMAE compared with those receiving usual care. HDCS may potentially help identify candidates for MMAE for nonacute SDH. Clinical trial registration no. NCT04700345 © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Kallmes in this issue.