Objective Middle meningeal artery embolization (MMAe) is a well-described minimally invasive approach in the management of chronic subdural hematomas (cSDH). The MMA typically arises from the external carotid artery and is one of the first branches off the internal maxillary division as it courses through the foramen spinosum to arrive intracranially. However, risks associated with the procedure exist as ectopic origins of the MMA - such as from the ophthalmic artery or aberrant anastomoses from its lacrimal branches to the ophthalmic artery territory - can result in inadvertent blindness or cranial neuropathies from non-target embolization. A pre-procedural indicator of MMA origin aberrancy maybe useful for guiding clinical decision-making for the safety of MMAe. This study aims to elucidate the possible correlation of the diameter of the foramen spinosum to the existence of an ectopic origin of the MMA or alternate anomalies that may preclude a successful embolization procedure.

Methods This retrospective analysis includes all patients having undergone MMAe from December 2018 to July 2022 in a single institution. Primary endpoint was defined as procedure completion with documented angiographic successful MMA embolization and follow-up imaging within minimum 30 days post MMAe. Cohort demographics, size of SDH on pre-procedural CT head, diameter of foramen spinosum on CT head, presence of aberrant MMA anatomy on angiography, reason for abortion of procedure if applicable, size of SDH on follow-up, and adjunct procedures performed such as SEPS, craniotomy, or subdural drain were recorded.

Results 131 NASDH patients underwent 172 MMAe. Patient demographics, procedural data, and statistical analyses are to be reported at the time of final presentation. Median range of foramen spinosum size as measured on the axial plane - referred to as the Spinosum Roentgen Index (S.R.I.) - was 2 to 3 mm long axis diameter. Spinosum size measurements were correlated with MMA size on angiography. S.R.I. values less than 2 or those in the 1.5 mm to 2 mm range led to one of the following clinical scenarios: A) small MMAs which often shut down too early with proximal PVA clumping, noting poor intraprocedural dural blush and less reduction in collection size on follow-up imaging; B) replaced MMA from normal variant such as ophthalmic artery, precluding subsequent embolization procedure; C) exploration of contralateral larger sized MMA yielded cross flow to the affected hemisphere.

Conclusions Assessment of pre-procedural head CTs prior to MMA embolization for not only subdural hematoma characteristics, but skull base osseous evaluation and S.R.I. recording has the potential to make neurointerventionalists aware of pitfalls that are otherwise experienced unexpectedly during a given procedure. This preliminary data suggests incorporation of S.R.I. values could be useful in the triaging of this rising-in-prevalence neurointerventional procedure. Such knowledge could alter one’s approach to embolization from the get-go, or perhaps not even proceed with intervention in small index values, thereby reducing patient risk and operator time commitment. Larger scale studies are needed to further validate this index.

Disclosures E. Hallman: None. Z. Shaff: None. S. Sundararajan: None. H. Nasser: None. R. Williams: None. B. Baxter: None. D. Shaff: None.