Discussion

The incidence of cSDH is projected to increase in the coming decades as the population ages. Potentially 60 000 Americans will experience a cSDH annually in the next 10 years.3 MMA embolization has emerged as an alternative treatment for cSDHs due to its minimally invasive nature and apparent efficacy. This procedure was first described by Mandai et al in 2000 with a single patient whose cSDH was successfully treated using MMA embolization.12 More recently, multiple case reports and series have suggested that MMA embolization is effective in the treatment of cSDH, with a high rate of hematoma resolution and a low rate of complications.12–19 For example, Link et al examined 60 cSDHs in 49 patients and found 41 patients (84%) to have hemorrhages that were stable or decreased in size with no significant procedural complications.9 Similarly, Ban et al analyzed 72 patients with cSDHs treated via MMA embolization and found only one patient with a treatment failure (defined as either rescue surgery and/or >10 mm of hemorrhage found on postoperative imaging), and no patients experienced complications.6 By comparison, in our study, only one patient (3%) experienced a treatment-related complication, and more than 97% of patients had successful MMA embolization with reduction of their hematoma without the need for additional interventions. Notably, the complication occurred early in our series in a patient with a type III arch for whom femoral access was used.

Given the significant vascular comorbidities often seen in this patient population, we subsequently began to assess aortic arch vessel imaging prior to these interventions and transitioned almost exclusively to a radial approach. Furthermore, of the cSDHs embolized, over 60% were completely resolved within 4–6 weeks on follow-up imaging.

Because MMA embolization for cSDHs remains a relatively novel procedure, direct comparison of techniques is lacking. Such evaluations are necessary to optimize this treatment. For instance, after entering the cranium through the foramen spinosum, the MMA courses through a groove in the greater wing of the sphenoid and divides into two branches, the anterior and posterior branches.20 In the present analysis, embolization of both branches (relative to a single branch) was associated with a significantly higher frequency of complete resolution of the hematoma. In fact, none of the patients who underwent embolization of both branches experienced treatment failure. Once the MMA divides into the anterior and posterior branches, both branches continue distally to supply the dura (the anterior branch divides into small distal branches at the sphenoid angle of the parietal bone that eventually reach the vertex and occipital region, whereas the posterior branch arcs on the squamosal portion of the temporal bone, eventually branching into small distal arteries, at the parietal bone in front of the mastoid angle, which supply the posterior dura of the cranium).20 In the current analysis, although none of the patients for whom both distal and proximal MMA embolization was accomplished experienced treatment failure, this comparison was not statistically significant.

The majority of previous studies reported the use of microparticles.6 9 11 21 Our analysis found no statistically significant difference between various embolic agents. Over time, we have transitioned to using Onyx for the majority of cSDH embolizations, and we have noted neither complications nor treatment failures using this material. Additionally, nearly 70% of the cSDHs embolized with Onyx completely resolved on short-term follow-up. Similarly, Waquas et al performed MMA embolization with Onyx in eight patients and reported no recurrences.21 Onyx may allow for deeper penetration, possibly preventing collateral vessel formation.22 Furthermore, Onyx or other liquid embolic agents are permanent, and their use may avoid delayed recanalization, which might occur with particles.22 However, it should be mentioned that owing to its potential to penetrate smaller vessels, Onyx must be used with caution in the presence of dangerous anastomoses, and existing variants of the MMA origin from the ophthalmic artery are possible.23 24 Moreover, knowledge of cranial nerve blood supply for embolization with any embolic agent is imperative. In particular, the petrous branch of the MMA is a significant supplier to the facial nerve. Injury to the nerve may cause debilitating neurological and cosmetic complications.23

It should be also remembered that injecting Onyx into the MMA is extremely painful, and thus general anesthesia or prior lidocaine injection is required.25 In our series, we performed the vast majority of these cases with the patient under general anesthesia to improve visibility during the injection. Given the medical frailty of these patients, an approach using conscious sedation may ultimately be preferred, or at a minimum, immediate postoperative extubation should be prioritized.

Traditionally, femoral artery access has been used for neuroendovascular procedures; however, successful treatments have been performed recently with radial artery access, which are associated with lower complication rates.26 During the study, our institution moved into a radial first practice due to these lower rates of access site complications. Of the 21 patients with radial access, none experienced a complication or treatment failure. Hence, a transradial approach for MMA embolization of cSDH provides similar treatment success to that of transfemoral access but without the potentially life-threatening access site complications.

Owing to its retrospective nature, this study is subject to all of the biases inherent in retrospective analyses, as well as those inherent in studies with small sample sizes. In addition, treatment approaches and outcome measures were determined on the basis of the on-call attending physicians’ preferences without a set institutional algorithm or protocols for follow-up imaging. However, in general, treatment approaches are primarily based on three categories: observation with or without medical treatment such as corticosteroids or statins in patients with small asymptomatic cSDHs <8 mm in diameter, MMA embolization or observation in patients without focal neurologic deficit with cSDHs ≥8 mm in diameter and with or without midline shift, surgery with or without MMA embolization in patients with symptomatic or large cSDH with >5 mm midline shift. Outcome measures are based on radiographic measure on monthly follow-up imaging and clinical measure using the mRS score. These factors impose further possible selection bias to this study.