Tapan Mehta, MBBS, MPH
Chronic subdural hematoma (SDH) can be challenging to manage. Although, surgical evacuation with craniotomy or burr hole are very effective interventions, the recurrence rates are reported to be more than 30% with a great variability. The incidence of chronic SDH in the age group 70-79 increases to 7.35/100,000 per year from an overall average population incidence of 1.72/100,000. Along with an increasing life expectancy, the incidence of cardiovascular diseases requiring antiplatelet and anticoagulant medications is also increasing. Patients who develop chronic subdural hematoma and stop antiplatelet/anticoagulant medications are not only at a higher risk for ischemic cardiovascular events, they also are typically high risk neurosurgical candidates for hematoma evacuation procedures. An alternative minimally invasive intervention could significantly impact this population.
Subdural hematoma (SDH) formation occurs due to the tearing of bridging veins. Chronic subdural hematomas are shown to develop an outer membrane with neovascularization along with the dura. Histopathological studies have shown ongoing inflammation at the site of chronic SDH and presence of angiogenic factors. The neovascularization with presence of very small arteries (50 mu) connecting to dural branches of the middle meningeal artery (MMA) have also been demonstrated. Theoretically, embolization of MMA would decrease the “leaking” of these vessels. Several retrospective studies have reported the possibility of usefulness of MMA embolization in specific setting of chronic subdural hematoma. Link et al. demonstrated that among the 50 cases treated with MMA embolization, 91.1% patients with chronic SDH (previously untreated or recurrent after surgical evacuation) were able to avoid surgery with clinical improvement and decrease in size of the hematoma. Ban et al., in a prospective cohort study of 541 chronic subdural hematoma patients (72 patients receiving MMA embolization and 469 receiving conventional treatment), demonstrated that the treatment failure rate in the MMA embolization group was lower than the conventional treatment group (1.4% vs 27.5%, adjusted odds ratio 0.056; 95% confidence interval: 0.011 – 0.286; P = .001). There are several similar case reports and case series published with good outcomes as of now.
Considering the benefit of distal penetration, most of the literature available favors using polyvinyl alcohol particles for embolization of middle meningeal artery in chronic recurrent SDH. However, little is known about recanalizations of the vessels in such cases, and how the dural vessels are affected. A majority of the published literature supports that MMA embolization in chronic SDH is safe. However, operators must have a detailed knowledge of anatomy, especially external to internal collaterals and their variations, in addition to experience with different embolic materials.
An ongoing clinical trial (NCT03307395) is investigating safety and efficacy of MMA embolization for symptomatic chronic medically refractory subdural hematoma. Although we would need more evidence before MMA embolizations become standard of care for chronic symptomatic SDH, the importance of this topic is likely to increase with an increase in proportion of elderly patients on lifelong antiplatelet and anticoagulation medications.