In Reply: Middle Meningeal Artery Embolization in Adjunction to Surgical Evacuation for Treatment of Subdural Hematomas: A Nationwide Comparison of Outcomes With Isolated Surgical Evacuation

To the Editor: We appreciate the important points raised by Su et al1 regarding our recent study entitled "Middle Meningeal Artery Embolization in Adjunction to Surgical Evacuation for Treatment of Subdural Hematomas: A Nationwide Comparison of Outcomes with Isolated Surgical Evacuation."2 In the latter study, we compared middle meningeal embolization (MMAE) as adjunctive treatment to surgery (S) with isolated surgical treatment in patients with chronic subdural hematoma (CSDH). Using aggregated data from the National Vizient Clinical Database, we demonstrated that patients undergoing MMAE + S experience lower recurrence and readmission rates despite having less favorable baseline comorbidities. The authors1 highlight the importance of considering middle meningeal artery diameter when choosing patients for primary or adjunctive MMAE. This is implied by the results of a recent multi-institutional study on a large sample, assessing predictors of MMAE failure, which found middle meningeal artery diameter to be the only predictor of failure after adjustment for several variables.3 Reduced delivery of the embolic agents through small middle meningeal arteries and alternative feeding arteries to the inner and outer membranes are considered the mechanisms behind the ineffectiveness of MMAE in this group. Su et al also mentioned their experience and several studies demonstrating that the presence of diffuse MMA dilation and scattered abnormal vascular networks (MMA staining) would not affect the embolization outcome. Moreover, in a recent study by Weinberg et al,4 membranous and nonmembranous hematomas had comparable outcomes after MMAE. Interestingly, in addition to the previous observations, the embolized branch (proximal vs distal), dominancy of the embolized branch (dominant vs nondominant), number of embolized branches (1 vs more than 1), or isolated use of coils have been found not to affect the risk of recurrence.5,6 All these unexpected findings are suggestive that nuances of CSDH resolution after MMAE have not yet been elucidated. Nonetheless, because our study used a national database providing aggregate data, we were unable to stratify and assess for such factors when conducting our analyses. It is worth mentioning that, currently, cerebral angiography is not routinely performed in patients with chronic subdural hematoma, and establishing its role as a routine preoperative workup would need future studies to evaluate how angiographic findings related to the hematoma would affect the outcome of MMAE. Su et al1 mentioned the need for the identification of patients who would benefit most from MMAE and that concluding the long-term benefit and cost-effectiveness of MMAE is premature. Although we agree with these comments, we believe our study provides, while with its limitations, valuable evidence to urge future studies on these subjects. Moreover, considering that MMAE is a novel intervention lacking evidence-based guidelines and consensus recommendations on its indication, with growing interest among neurosurgeons and interventional neurologists, we believe that such a nationwide study reflecting the current state of MMAE in practice would be of equal importance, if not more, compared with clinical trials recruiting selective subjects among target populations. Furthermore, regarding the cost-effectiveness of MMAE, several previous studies have found MMAE to be associated with less or comparable overall cost compared with conventional treatments when taking reduced recurrence into account, highlighting that MMAE is a cost-effective alternative treatment option.7-9 Finally, emphasizing the points made by Su et al,1 we would like to encourage future studies to investigate the controversial observations regarding factors affecting the outcome of MMAE and preoperative workup required for patient selection for MMAE, while we await the results of several ongoing trials on the efficacy of MMAE.