Abstract

Background: Middle meningeal artery embolization (MMAe) has emerged as a safe and efficacious treatment for chronic subdural hematoma (cSDH). Performing this procedure on an outpatient basis has the opportunity to accelerate recovery and provide economic advantages. However, data supporting such protocols remain limited. This study aims to substantiate the feasibility of outpatient MMAe by describing its success at our institution.

Methods: A single-center retrospective cohort analysis of all patients undergoing outpatient MMAe for cSDH was conducted between August 2023 and March 2025. Primary outcomes included procedural complication rates, postprocedural emergency department (ED) return rates, and 30-day readmission rates. Secondary outcomes included hematoma recurrence or expansion, degree of symptom resolution, and radiographic outcomes.

Results: 64 patients were included in the analysis, with a median age of 76 years (interquartile range [IQR]: 68–80). The majority of embolizations (77%) served as primary treatment. The median hematoma depth was 11 mm (IQR 7–15), with bilateral hematomas present in 42% of cases. No intra-procedural complications occurred; however, two patients suffered minor postprocedural complications. The 30-day readmission rate was 5% (n = 3), with no readmissions within 48 h. 17% of patients (n = 11) returned to the ED – the median time from embolization to ED presentation was 12 days (IQR 4–17 days). Among 52 patients (81%) with long-term follow-up, 4% suffered hematoma recurrence requiring surgical drainage, 58% achieved complete resolution of symptoms, and 29% showed improvement in symptoms.

Conclusion: The study suggests that outpatient MMAe can be both safe and feasible for select patients with cSDH.

Keywords: Endovascular, Middle meningeal artery embolization, Outpatient, Protocol, Subdural hematoma

INTRODUCTION

Chronic subdural hematoma (cSDH) is an extremely common neurosurgical condition with an estimated annual incidence of up to 20/100,000 persons.[ 8 ] Traditional management typically includes either craniotomy, bedside drainage, or conservative monitoring with serial imaging.[ 8 ] However, middle meningeal artery embolization (MMAe) has emerged as an extremely safe, minimally invasive, and highly efficacious alternative, both in the form of adjunctive and primary treatment for cSDH.[ 2 , 9 , 16 ] With the recent publication of several large-scale randomized controlled trials, it also represents a rapidly evolving field of neurosurgical investigation.[ 2 , 9 , 16 ]

In addition to its efficacy, much of the utility of MMAe can be attributed to its minimally invasive nature, including transradial access and conscious sedation, both of which allow for early mobilization. Embolization addresses the underlying pathophysiology of the hematoma’s chronicity by disrupting the blood supply to the hematoma’s neomembrane and thus leads to lower rates of recurrence.[ 1 ] MMAe has notable economic benefits as well. Given its low complication rate and anesthetic burden, patients typically spend less time in the hospital, require fewer resources and thus, incur lower hospital costs compared to prolonged inpatient hospitalizations associated with craniotomy.[ 12 ]

These advantages lead to one question: can MMAe for cSDH be routinely performed on an outpatient basis? Our experience suggests that the answer is yes. In our practice, we have consistently achieved success in safely performing both primary and adjunctive MMAe’s on an outpatient basis. This success is largely due to our approach to vascular access, sedative choice, and early mobilization efforts. Thus, in this article, we share the framework of our outpatient MMAe protocol, including an analysis of our patient demographics, clinical and radiographic variables, and outcomes to substantiate the efficacy and generalizability of this protocol. In doing so, we aim to enable other endovascular specialists and their patients to benefit from this innovative approach to cSDH management.

MATERIALS AND METHODS

Study design

A retrospective analysis of all patients who had undergone outpatient MMAe for cSDH over a 20-month period between August 2023 and March 2025 was conducted. Embolizations were classified as outpatient when patients underwent embolization and were discharged from the hospital on the same day. Before embolization, all patients had initially received neurosurgical evaluation with diagnosis and management of subdural hematoma in the acute hospital setting. The senior author treated all patients included in the analysis at our institution. Immediately following their procedure, patients recovered in the postanesthesia care unit until fit for discharge home. Demographic, clinical, radiologic, and procedural details were collected up to the most recent follow-up period. Neurologic status was quantified using the Glasgow Coma Scale (GCS) at the time of clinic evaluation, immediately preembolization, at the time of discharge, and at the time of last follow-up. The severity of clinical presentation was stratified using the Markwalder grading scale (MGS),[ 19 ] which is a 5-point scale (0–4) that has been frequently employed to assess the neurological status of patients with cSDH.[ 2 , 19 , 22 ] The grading scale is as follows: MGS 0 (no neurologic abnormalities), MGS 1 (alert and oriented; headache or mild deficits), MGS 2 (disoriented or drowsy; moderate focal deficit), MGS 3 (severely depressed consciousness; severe focal deficit such as hemiparesis), or MGS 4 (comatose with no motor response to noxious stimuli). For the purposes of our cohort, MGS 0–1 was classified as mild clinical presentation, MGS 2 as moderate, and MGS 3–4 as severe. Patients were excluded if no clinical follow-up data were available. Hematoma depth was rigorously validated through a two-step process: primary reliance on formal radiology reports generated by board-certified neuroradiologists, and for reports lacking an explicitly stated hematoma depth, performance of measurements by an independent board-certified neuroradiologist within the IntelliSpace Radiology Portal (© Koninklijke Philips N.V, Nashville, TN).

Outcomes and follow-up

The primary outcomes that were measured included the procedural complication rate, emergency department (ED) return rate for hematoma or embolization-related symptoms, and the 30-day readmission rate for hematoma or embolization-related symptoms. Secondary outcomes included hematoma recurrence or expansion (defined as recurrence of preprocedural symptoms or new symptoms attributed to an increased hematoma volume observed on imaging), degree of symptom resolution (classified as complete resolution of, improvement in, no relief, or worsening of preembolization symptoms), and radiographic outcome (defined as complete regression of hematoma, decrease in hematoma size, no change in hematoma size compared to preprocedural imaging, or hematoma expansion).

Statistical analysis

Data analysis was performed using the Statistical Package for the Social Sciences Version 25 (IBM Corp, Armonk, NY, USA) and Jamovi (The Jamovi Project, open source). Continuous variables were summarized as medians with interquartile ranges (IQRs), and categorical variables were summarized as frequencies with percentages.

Ethical considerations

The study was conducted in accordance with The Code of Ethics of the World Medical Association. It also followed institutional guidelines, laws, and ethical standards and received approval from the institutional review board (Reference Number 11121, 2025). As a retrospective chart review, patient consent was not required, but confidentiality and data protection measures were strictly adhered to throughout the study process. All reporting has been made in line with STROBE Guidelines.[ 25 ]

RESULTS

Patient selection

64 patients (n = 64) underwent outpatient MMAe during the specified time period and were included in the final analysis. A summary of the demographic data can be found in Table 1 . The median age at treatment was 76 years (IQR 68–79.5 years), with a slight male predominance (64%, n = 41). Hypertension and hyperlipidemia were the most prevalent comorbidities in our cohort, present in 80% (n = 51) and 73% (n = 47) of patients, respectively. This was followed by coronary artery disease (34%, n = 22), diabetes (34%, n = 22), and heart failure (17%, n = 11). Just under half of patients (47%, n = 30) had no smoking history, while 41% (n = 26) were former smokers, and 13% (n = 8) were current smokers. 27% (n = 17) of patients were taking some form of anticoagulation or antiplatelet therapy at the time of embolization: this included five patients on apixaban or rivaroxaban alone (n = 5), one patient on apixaban and aspirin (n = 1), eight on a single antiplatelet agent alone (n = 8), and three on dual antiplatelet therapy alone (n = 3).

Table 1:

Baseline patient demographics.

Clinical characteristics

A delineation of clinical characteristics and procedural metrics is provided in Table 2 . The most prevalent symptom at the time of evaluation was headache, affecting 69% of patients (n = 44), followed by gait instability (33%, n = 21) and light-headedness (23%, n = 15). Mild cognitive impairment was present in 15 patients (23%), including confusion in seven patients (11%, n = 7). 8% of patients (n = 5) presented with weakness. Of note, one patient with preexisting dementia demonstrated cognitive dysfunction at the time of evaluation but for the sake of data collection was not classified as presenting with cognitive impairment as it was present at baseline before developing cSDH.

Table 2:

Clinical and procedural characteristics.

Notably, 36% (n = 23) of patients presented with other miscellaneous symptoms including nausea or vomiting, visual disturbances, paresthesia, or seizure-like episodes, while 5% (n = 3) were asymptomatic. Although asymptomatic, these three patients underwent MMAe due to concern for progressing hematomas with associated radiographic evidence of mass effect, in conjunction with the patients’ preferences for minimally-invasive management.

The severity of presentation, as assessed by the MGS, revealed that the vast majority of patients (89%, n = 57) exhibited mild symptoms (MGS 0–1), with approximately 10% (n = 7, 11%) presenting with moderate symptoms markwalder grading scale (MGS 2). The most common American Society of Anesthesiology scores were 3 (52%, n = 33) and 2 (34%, n = 22); 14% of patients (n = 9) did not have a score reported.

The median preembolization hematoma depth was 11 mm (IQR 7–15 mm). Regarding hematoma laterality, 42% (n = 27) of cases were bilateral, while 28% (n = 18) were left-sided and 30% (n = 19) were right-sided. Over half of patients (53%, n = 34) demonstrated midline shift, with a median shift of 4 mm (IQR 3–5 mm).

Procedural metrics and complications

In terms of treatment classification, the majority of embolizations (77%, n = 49) served as primary treatment, while 23% (n = 15) were performed after surgical evacuation (that occurred during a previous, separate encounter) had failed to treat the patient’s hematoma [ Table 2 ]. For these adjuvant cases, the median time from surgical intervention to embolization was 24 days (IQR, 6–41 days). Conscious sedation was utilized for 69% (n = 44) of procedures, and the remaining 31% (n = 20) performed under general anesthesia. Of the cases performed with conscious sedation, the median cumulative midazolam dose was 2.75 mg (IQR, 2–4 mg), and the median cumulative fentanyl dose was 87.5 mcg (IQR, 50–137.5 mcg). A dexmedetomidine drip was also utilized in all of these cases.

All but seven procedures were performed through right radial access (89%, n = 57); two cases (3%) were performed through right ulnar access, and five cases (8%) required conversion from radial to femoral access. Liquid embolic agents were used in 95% (n = 61) of procedures, with three (n = 3) of these cases utilizing a combination of liquid embolic agent and coiling. Alternatively, coiling alone was utilized in 5% (n = 3) of cases. In all instances, Onyx^™ 18 (Medtronic, Minneapolis, MN) was the embolic agent used and Avenir^® (Wallaby Medical, Laguna Hills, CA) was the coil system used for embolization.

Procedure duration varied based on laterality, with unilateral procedures lasting a median of 67 min (IQR 53–85 min) and bilateral procedures lasting a median of 88 min (IQR 67– 137 min). For access site closure, TR^™ bands (Terumo Medical Corporation, Somerset, NJ) were utilized in transradial cases, with both a TR^™ band and MYNX CONTROL^® Vascular Closure Device (Cordis. Miami Lakes, FL) being used for the cases requiring conversion to transfemoral access.

Primary outcomes

A summary of primary outcomes can be found in Table 3 . No intra-procedural complications were reported. Two patients (3%, n = 2) experienced minor immediate postprocedural complications, both of which were access site hematomas. None of these patients were on antiplatelet or anticoagulation agents before their procedure.

Table 3:

Primary outcomes.

The 30-day readmission rate was 5% (n = 3). Reasons for readmission included one patient with hematoma recurrence (manifested by hemiplegia and word-finding difficulty) on postembolization day 28 requiring surgical evacuation, a patient with acute kidney injury unlikely to have been related to the procedure (but included due to its 4-day proximity to embolization), and a patient suffering from a posterior-territory ischemic stroke 3 days after embolization. However, when considering that this patient’s infarct occurred on the side opposite of embolization, along with radiographic evidence of stenosis of the posterior cerebral artery ipsilateral to the infarct, it is unlikely that the patient’s MMAe was responsible for this event. In addition, a fourth patient did require readmission for surgical evacuation of a recurrent hematoma, but this occurred 45 days postembolization.

11 patients (17%, n = 11) returned to the ED following MMAe for procedure or hematoma-related complications, with a median time from embolization to ED presentation of 12 days (IQR, 4–17 days). Of these patients, only one (2%, n = 1) presented within 48 h postembolization, which was a case of postprocedural internuclear ophthalmoplegia developing in a delayed fashion several hours after returning home. This patient did not require readmission and experienced complete resolution of their symptoms by the time of their next follow-up. Beyond this patient and the four previously-mentioned cases of readmission, the remaining 6 patients presenting to the ED experienced only transient episodes for which they were sent home on the same day: these included (1) an episode of gait, vision, and word-finding difficulty, (2) an episode consisting of headache, word finding difficulties, and vision changes, (3) a patient with a brief experience of paresthesia and blurry vision, (4) a patient with isolated upper extremity weakness (and radiographic evidence ruling out acute infarct), and (5,6) two instances of near-syncopal episodes. All six patients were able to be safely sent home on the same day of presentation, and all six experienced complete resolution without sequelae by the time of their next follow-up in the clinic.

Secondary outcomes: Clinical

A secondary outcomes summary is provided in Table 4 . Long-term clinical follow-up data were available for 52 patients (81%), with a median follow-up duration of 2.3 months (IQR 1–4.5 months). Regarding symptom resolution at the last follow-up, more than half of patients (58%, n = 30) experienced complete resolution of their preembolization symptoms. An additional 29% (n = 15) demonstrated improvement in their preembolization symptoms, while 13% (n = 7) did not experience any benefit. Regarding neurologic status at the last follow-up, all but one patient (98%, n = 51) displayed a GCS of 15. Of note, the one outlier had a history of dementia and had been confused at baseline before developing their cSDH (GCS 14, 2%, n = 1). Four patients (8%, n = 4) experienced recurrence of their hematoma following embolization, two of which manifested as hemiparesis and were the previously mentioned patients requiring hospital admission for surgical evacuation. The other two patients experienced worsening of their preembolization symptoms accompanied by radiographic evidence of hematoma expansion; however, both episodes of recurrence resolved by the time of final follow-up.

Table 4:

Clinical and radiographic outcomes.

Outcomes: Radiographic

Radiographic outcomes were documented in 52 patients (81%), with a median radiographic follow-up duration of 9 weeks (IQR 5.6–20.6). An exemplary radiographic timeline of one of our patients is provided in Figure 1 . At the time of final radiographic follow-up, approximately a third of patients (33%, n = 17) demonstrated complete regression of their hematoma, 58% of patients (n = 30) exhibited partial regression, 10% (n = 5) showed stable hematoma size, and none (0%, n = 0) demonstrated expansion.

Figure 1:

(a and b) Computed tomography (CT) scans of a patient in their 70’s demonstrating a subdural hematoma over the left cerebral convexity measuring approximately 2 cm in thickness. (c and d) 6-month follow-up CT demonstrated resolution of the hematoma.

DISCUSSION

MMAe has radically transformed the management of cSDH. At its core, the pathophysiology of cSDH consists of a tightly woven interplay between inflammation, angiogenesis, and microhemorrhage.[ 5 ] More specifically, the presence of blood beneath the dural space creates an inflammatory environment rich in vascular growth factors.[ 11 ] This subsequently drives the formation of friable, immature vasculature prone to bleeding, and establishes a self-perpetuating cycle of microhemorrhage and inflammation that maintains the chronicity of the hematoma. MMAe directly combats this process by terminating the hematoma’s blood supply, thus placing a halt on the underlying feedback loop and allowing the hematoma to regress.

In this study, we present a retrospective cohort of 64 patients who underwent outpatient MMAe for cSDH, with the goal of evaluating the feasibility and safety of this approach. Importantly, our study found no readmissions within 48 h following outpatient MMAe, a finding that strengthens the case for both the feasibility and safety of same-day discharge protocols. This is particularly relevant when considering the brevity of a typical inpatient admission for MMAe, which is unlikely to capture any complications that otherwise would not have been caught in the immediate postprocedural recovery period. Indeed, while hospital length of stay following MMAe varies across institutions, our data indicate that complications did not cluster in this early postprocedural window. Thus, complications that arise beyond this window would not have been prevented or managed differently had the embolization been performed on an inpatient basis. This suggests that routine inpatient admission may not offer meaningful additional clinical benefit and instead may expose patients to the potentially unnecessary risks and costs associated with hospitalization. This perspective is consistent with the broader endovascular literature, where outpatient treatment paradigms for procedures such as cerebral angiography and aneurysm coiling have been repeatedly implemented in a safe and successful manner.[ 7 , 21 , 27 , 28 ] Taken together, these findings argue that outpatient MMAe is not only a safe alternative to inpatient care but also in many cases may represent the more pragmatic and patient-centered approach.

Recently published evidence from three large-scale, multicenter randomized controlled trials (EMBOLISE, STEM, AND MAGIC-MT) has convincingly demonstrated not only the efficacy but also the impressive periprocedural safety profile of MMAe for cSDH.[ 2 , 9 , 16 ] All three studies show consistently low rates of major complications and no significant increase in short-term adverse outcomes when utilized both alone and as an adjunct to conventional management.[ 2 , 9 , 16 ] The data from our institutional cohort aligned with these findings, with over 85% of patients achieving resolution or improvement of symptoms.

The demographic similarities between our patient cohort and those of the large-scale trials strengthen the argument for performing this procedure on an outpatient basis. In addition, our cohort, although limited by its comparatively small sample size and retrospective design, also includes a significant proportion of patients with bilateral disease – an exclusionary characteristic in several of these trials. Furthermore, of the 18 patients on preprocedural anticoagulation or antiplatelet agents, none experienced complications related to their procedure or recurrence of their hematomas. Taken together, these findings underscore the efficacy of MMAe for cSDH and thus support the wide-reaching applicability of its implementation on an outpatient basis.

Description of outpatient protocol

Our outpatient protocol encompasses several key components with the goal of optimizing procedural efficiency as well as patient comfort and safety: this begins as soon as the patient is evaluated in the clinical setting. For example, special care must be taken when managing a patient’s outpatient medications in the periprocedural setting – this is especially true for anticoagulation or antiplatelet therapy. In such instances, we follow a standardized institutional protocol in which these agents are typically discontinued before the procedure and held for 3-month postembolization, if medically safe. For patients at risk of critical thrombosis, such as those with recent cardiac stent placement, atrial fibrillation, or upcoming cardiac procedures, the relevant specialist is consulted to determine the appropriate management of the patient’s antiplatelet or anticoagulant therapy. Procedurally, we preferentially utilize right radial access, as evidence has demonstrated that this reduces the risk of access-site complications, provides more comfort for the patient, and encourages earlier ambulation.[ 3 , 30 ] Specifically in MMAe, the transradial approach has been shown to decrease procedure time and risk for postoperative delirium without sacrificing technical feasibility, complication rates, or functional outcomes. [ 13 , 26 , 31 ] Regarding anesthetic management, procedures are performed, if possible, under conscious sedation with dexmedetomidine, as it allows us to minimize respiratory depression while maintaining adequate sedation.[ 4 , 10 , 24 ] Before embolization, lidocaine is locally administered through intra-arterial catheter to mitigate the trigeminocervical reflex,[ 18 , 29 ] which reduces unwanted movement and minimizes the risk of hemodynamic instability.[ 14 ] Immediately following the procedure, TR^™ bands (Terumo Medical Corporation, Somerset, NJ) are used to facilitate closure and hemostasis. We do not perform postprocedural imaging before discharge for the majority of patients. In the clinic setting, follow-up imaging is obtained at least once in all patients and then on an as-needed basis thereafter.

Economic implications

The implementation of outpatient MMAe protocols has the potential to create significant cost savings. This is primarily due to the fact that same-day discharges bypass the accumulation of inpatient hospitalization costs. When considering that a large majority of the cSDH patient population is comprised of Medicare beneficiaries over the age of 65,[ 15 , 23 ] in addition to evidence showing that elderly patients are especially prone to complications the longer they remain hospitalized,[ 17 ] the economic benefits are further amplified. The streamlined recovery afforded by these protocols also has the potential to decrease indirect costs associated with time away from employment. Although one recent study from Hung et al.[ 12 ] compared the costs of different levels of inpatient care in MMAe patients, a formal cost analysis of inpatient versus outpatient MMAe has yet to be performed. Such an investigation would provide valuable insight into the development of outpatient MMAe protocols.

Future directions

Several groups of authors have described the benefits of same-day discharge paradigms for their endovascular patients.[ 7 , 21 , 27 , 28 ] This was initially proposed for MMAe amidst the COVID-19 crisis[ 6 ] and has since been gaining momentum as institutions recognize its ability to reduce healthcare utilization and costs while offering a similar safety profile to inpatient embolizations.[ 20 ] This growing body of literature should help other interventionalists develop similar protocols. MMAe comprises a small portion of the overarching field of neuro-endovascular intervention, and the cSDH patient population represents a unique subgroup of this larger endovascular population. Multicenter studies are needed to validate our findings.

Limitations

This study has several limitations, including both its single-center, retrospective design and its limited sample size of 64 patients. Given the specific focus of this study on outpatient MMAe, our cohort’s clinical and radiographic characteristics may differ from those of the typical cSDH patient and thus reflect an inherent selection bias in our study design. This is evidenced by the relatively small midline shift (median 4 mm, IQR 3–5 mm) present at baseline in our cohort compared to other study populations[ 2 , 9 , 16 ] and highlights the importance of considering a patient’s entire clinical and radiographic presentation when deciding if they are a candidate for outpatient embolization. Finally, all embolizations in this study were performed by a single interventionalist and thus reflect their individualized practice patterns and potentially limit the generalizability of our results.

CONCLUSION

This study offers encouraging preliminary evidence that outpatient MMAe can be both safe and effective for cSDH. Taken together, outpatient MMAe represents the opportunity to align clinical efficacy, accelerated recovery, and economic benefit. Multicenter studies are needed to validate the findings of the study.

Ethical approval:

The research/study was approved by the Institutional Review Board at OUHSC Institutional Review Board, number 11121, dated March 2025.

Declaration of patient consent:

Patient’s consent not required as patient’s identity is not disclosed or compromised.

Financial support and sponsorship:

Nil.

Conflicts of interest:

Dr. Shakir is a consultant for the following companies: ©Terumo, ©Stryker, ©Imperative Care Inc., and ©Q’Apel Medical Inc.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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