Complete resolution of massive chronic subdural hematoma with refined layered middle meningeal artery embolization: A case report

Abstract

BACKGROUND

Chronic subdural hematoma (cSDH) is typically surgically managed; however, middle meningeal artery embolization (MMAE) has recently gained attention as a minimally invasive alternative. Optimal embolization techniques and patient selection criteria remain under investigation. Here, we present a refined embolization strategy - the layered embolization technique - which enhances distal penetration and procedural safety, representing a potential advancement in MMAE for cSDH.

CASE SUMMARY

A 78-year-old female with bilateral symptomatic cSDH and significant mass effect was unsuitable for surgery due to advanced age, comorbidities, and religious considerations. Standalone MMAE using a refined layered technique achieved complete hematoma resolution and full brain re-expansion within 3 months, without complications. The layered embolization technique involved initial deep penetration of the distal neovascular branches using low-concentration particles, followed by proximal vessel occlusion with standard-concentration particles under continuous fluoroscopic guidance. This controlled approach optimizes distal embolization, minimizes premature reflux, and facilitates complete hematoma clearance. Our case illustrates the potential for broader application of upfront MMAE, even in symptomatic cSDH with large hematomas.

CONCLUSION

Standalone MMAE using layered embolization is safe and effective for managing cSDH with significant mass effect in high-risk surgical candidates.

Key Words: Chronic subdural hematoma; Significant mass effect; Middle meningeal artery embolization; Layered embolization technique; Complete resolution; Case report

Core Tip: This case demonstrates a refined layered embolization technique as a novel approach for treating chronic subdural hematoma with significant mass effect. By employing sequential low- and standard-concentration embolic suspensions, the technique achieves deep distal penetration and proximal sealing, facilitating complete hematoma clearance within three months. This approach expands the therapeutic role of middle meningeal artery embolization to high-risk or surgically unsuitable patients.

INTRODUCTION

Chronic subdural hematoma (cSDH) is a common neurological condition with an annual incidence of approximately 10 per 100000 individuals. Moreover, with population aging and the widespread use of antiplatelet and anticoagulant medications, the prevalence of cSDH is rising[1,2]. Surgical evacuation remains the standard treatment for symptomatic cases, particularly those with significant mass effect[1,2]. Middle meningeal artery embolization (MMAE) has recently emerged as a minimally invasive alternative to surgery[3-5]. However, technical refinements to enhance safety, efficacy, and hematoma clearance remain underexplored. Here, we report a case of massive cSDH with substantial mass effect successfully treated with standalone MMAE using a refined layered embolization technique, achieving complete hematoma resolution. This case highlights the potential of this novel strategy and the broader applicability of MMAE in high-risk or surgically unsuitable patients.

CASE PRESENTATION

Chief complaints

A 78-year-old female presented with preserved consciousness, slurred speech, and right-sided weakness.

History of present illness

This 78-year-old woman had sustained a head injury after a fall two weeks earlier. She subsequently developed an acute onset of slurred speech and right-sided weakness during the night on the day of presentation.

History of past illness

The patient had a medical history of hypertension, dyslipidemia, and gout. She underwent surgery for a thyroid nodule 28 years ago and surgery for genital prolapse 12 years ago.

Personal and family history

The patient is a 78-year-old female who is illiterate, widowed, and speaks Mandarin and Minnanese. She has no known drug or food allergies. She denies cigarette smoking, alcohol consumption, and betel nut use, and reports no travel history within the past three months. Her diet is regular, although she avoids beef. She received an influenza vaccination in 2023. Her family history is unremarkable, with no reported diabetes mellitus, hypertension, or cancer. She is primarily cared for by her three adult children (two sons and one daughter).

Physical examination

On admission, the patient was alert with a preserved mental status (Glasgow Coma Scale: E4V5M6). Neurological examination revealed right-sided weakness, with muscle strength in the right upper and lower limbs graded as 4/5 on the Medical Research Council scale, indicating movement against gravity with some resistance. Sensory examination, including pain perception, was normal.

Laboratory examinations

Routine blood tests, including complete blood count, electrolytes, coagulation profile, blood biochemistry, and immune and infection markers, were all within normal limits. Routine urine analysis and urinary sediment examination revealed no abnormal findings. Routine fecal testing, including occult blood testing, was also unremarkable.

Imaging examinations

Brain computed tomography (CT) demonstrated bilateral cSDH with mass effect (3.3 cm on the right and 1.64 cm on the left). Selective pre-embolization angiography of the middle meningeal artery (MMA) revealed the anterior and posterior branches supplying the external membranes of the hematomas, demonstrating a contrast blush indicative of pathological neovascularization (Figure 1).

Figure 1 Selective middle meningeal artery angiograms during embolization. A: Posterior branch angiogram demonstrating the anterior (a) and posterior (b) middle meningeal artery branches. Contrast blush (black arrow) denotes pathological neovascularization of the dural membranes, with the microcatheter tip positioned distally within the posterior branch (white arrowhead); B: Anterior branch angiogram demonstrating the anterior (a) and posterior (b) middle meningeal artery branches and the meningo-ophthalmic artery anastomosis (c), with contrast blush indicating pathological neovascularization (black arrows) and the microcatheter tip advanced beyond the meningo-ophthalmic origin to prevent reflux (white arrowhead).

FINAL DIAGNOSIS

The final diagnosis was massive cSDH with substantial mass effect.

TREATMENT

Given the patient’s advanced age, comorbidities, and personal religious considerations, MMAE was selected as the treatment instead of surgical evacuation. To minimize the risk of non-target embolization, hazardous anastomoses - particularly with the ophthalmic artery - were carefully identified, and the microcatheter was advanced beyond the origin of the meningo-ophthalmic artery to prevent reflux.

Embolization was performed using spherical polyvinyl alcohol (PVA) particles (Embozene^™, 400 μm, 2 mL) initially suspended in 5 mL of non-ionic iodinated contrast medium (iohexol, 370 mg/mL), yielding a standard-concentration suspension with a 1:2.5 (v/v) particle-to-contrast ratio. To facilitate deeper distal penetration into the pathological microvascular network, a low-concentration suspension was prepared by diluting a 3.5-mL aliquot of the standard suspension (containing 1 mL of PVA particles) with an additional 3.5 mL of iohexol, resulting in a final 1:6 (v/v) ratio. The preparation protocols and clinical objectives for both embolic concentrations are summarized in Table 1.

Table 1 Preparation and clinical objectives of the layered embolization technique.

Suspension	PVA particles (mL)	Contrast medium (mL)	Ratio (v/v)	Clinical objective
Standard concentration	2	5	1:2.5	Proximal sealing and vessel stasis
Low concentration	1	6	1:6	Deep penetration of distal neovascular network

PVA: Polyvinyl alcohol; v/v: Volume-to-volume ratio.

A layered embolization technique was employed. The microcatheter was first advanced distally into the selected MMA branch, where the low-concentration suspension was slowly injected to achieve deep penetration of the neovascular network. This was followed by the administration of the standard-concentration suspension to fill and seal the proximal MMA branches, ensuring robust and complete vascular occlusion.

The injection proceeded under continuous fluoroscopic guidance until complete vessel stasis was confirmed angiographically. Intraprocedural cone-beam CT following MMAE demonstrated contrast penetration into the subdural space (Figure 2), consistent with deposition of PVA particles.

Figure 2 Axial intraprocedural cone-beam computed tomography before and after middle meningeal artery embolization. A: Pre-embolization computed tomography; B: Post-embolization computed tomography demonstrating contrast penetration into the subdural space (black arrows), indicative of spherical polyvinyl alcohol particle deposition.

OUTCOME AND FOLLOW-UP

Follow-up CT scans at 1, 2, and 3 months post-procedure showed complete hematoma resolution and significant brain re-expansion (Figure 3). No procedure-related complications occurred.

Figure 3 Axial brain computed tomography showing progressive resolution of chronic subdural hematoma following middle meningeal artery embolization. A: Pre-embolization image illustrating extensive bilateral chronic subdural hematoma; B: One-month post-embolization image showing substantial hematoma reduction; C: Two-month post-embolization image demonstrating continued hematoma clearance; D: Three-month post-embolization image showing complete hematoma resolution and excellent brain re-expansion.

DISCUSSION

MMAE is increasingly recognized as a safe and effective minimally invasive treatment for selected patients with cSDH[1,4,5]. Current guidelines recommend its use in patients with mild symptoms or small hematomas (< 10 mm thickness and < 5 mm midline shift), while surgical evacuation remains the first-line therapy for patients with large hematomas or neurological deficits[4,5]. Accordingly, the role of upfront MMAE in patients with significant mass effect is uncertain. Our case demonstrates the successful use of a refined layered embolization technique - designed to enhance distal penetration and proximal sealing - achieving complete hematoma resolution and potentially broadening the applicability of MMAE to high-risk or surgically unsuitable patients.

MMAE has been validated as an effective adjunct to standard therapy, significantly reducing recurrence and treatment failure, without increasing major complications[3-5]. The scanning transmission electron microscopy trial (a randomized controlled trial) further showed that, in the non-surgical standard-treatment subgroup, primary MMAE reduced the rate of treatment failure from 56% to 19%[5]. Additional studies support the favorable safety of standalone MMAE, reporting lower recurrence rates and fewer complications compared with surgery, particularly in older patients, those with multiple comorbidities, or individuals receiving long-term antiplatelet or anticoagulant therapy[1,2]. Nonetheless, patients with larger hematomas are typically directed to surgery, resulting in substantially larger hematomas in the surgical cohorts of current trials. Refinements in embolization technique remain underexplored, and studies evaluating technical modifications to enhance efficacy and safety are lacking. Our proposed layered embolization strategy improves the stability of particle deposition and, more importantly, expands the role of MMAE for patients currently considered unsuitable for standalone embolization.

Liquid embolic agents, such as Onyx and n-butyl cyanoacrylate, provide excellent distal penetration and real-time visualization. However, their clinical application is frequently constrained by high costs, technical complexity, and inherent risks, including dimethyl sulfoxide toxicity, catheter entrapment, and unintended proximal vessel sacrifice resulting from microcatheter reflux[6-8]. In contrast, particle-based agents offer a more cost-effective alternative with a favorable safety profile derived from their biocompatibility and technical simplicity[7,9]. Notably, comparative studies of MMAE for cSDH have demonstrated no significant differences in success, recurrence, or surgical rescue rates when comparing PVA particles to liquid agents[7,8,10].

Nevertheless, particle delivery often encounters the “log-jamming” effect, where inter-particle friction causes premature proximal occlusion, preventing distal saturation[8,11]. While microcatheter distalization has been shown to improve distal deposition and increase complete resolution rates[12,13], our layered embolization technique advances this concept by strategically modulating flow dynamics to enhance distal delivery.

Initially, a low-concentration suspension preserves laminar flow, ensuring that the 400-μm microspheres behave as discrete units. This minimizes inter-particle friction and facilitates delivery to the absolute geometric limits of the pathological vascular bed[11]. A subsequent transition to a standard-concentration suspension promotes proximal stacking, forming a dense embolic column. This sequential layering ensures comprehensive distal saturation and durable devascularization. By optimizing rheological delivery, this technique circumvents the limitations of conventional particle-based agents, achieving the deep penetration typically associated with liquids while maintaining the safety profile of particles.

The selection of 400-μm calibrated microspheres for MMAE optimizes safety by integrating anatomical morphometrics with neovascular pathophysiology[7,11,14]. This diameter provides a geometric barrier against non-target embolization through hazardous extracranial-intracranial anastomoses, specifically those supplying the ophthalmic circulation and the vasa nervorum of cranial nerves[7,15,16]. Because critical pathways - such as meningo-ophthalmic anastomoses (100-300 μm), the central retinal artery (approximately 160 μm), and microvascular nerve supplies - overlap with smaller particle sizes (150-250 μm), 400-μm microspheres are physically precluded from these vessels. This size threshold effectively eliminates the risk of iatrogenic blindness or ischemic neuropathy, such as facial nerve palsy, during potential hemodynamic reversals[7,15,16]. Additionally, by preventing distal penetration into micro-collateral networks (< 100 μm), 400 μm microspheres preserve physiological perfusion to the surrounding healthy tissue and scalp, mitigating the risk of ischemic necrosis[11,14,17,18].

The therapeutic target in cSDH is the neovascular outer membrane, characterized by fragile macrocapillaries (sinusoids) fed by hypertrophied arterial branches[1,14,19]. The 400-μm particle is precisely calibrated to the distal MMA trunks (400-800 μm) and the origins of neovascular feeders (100-400 μm)[15]. By occluding the arteriolar level, these spheres “close the tap” on the vascular nidus, arresting the exudative cycle[9,11,14]. Clinical evidence suggests that 300-500-μm particles maintain comparable efficacy and success rates while reducing the risk of non-target complications compared to smaller 150-250-μm PVA particles[7,9,11].

The paradigm shift toward MMAE for cSDH represents a transition toward targeted, low-stress solutions in personalized geriatric neurosurgery[2,14]. The decision to prioritize MMAE over conventional drainage often lies at the intersection of biological risks, such as high recurrence associated with cerebral atrophy[8], and physiological constraints, specifically low anesthetic tolerance[9]. Conventional interventions, such as burr-hole craniostomy, typically necessitate general anesthesia, posing significant risks to patients with severe systemic comorbidities (American Society of Anesthesiologists Class III/IV) or high frailty (Modified 5-item Frailty Index ≥ 2)[20,21]. For these vulnerable populations, the physiological stress of endotracheal intubation and the elevated risk of postoperative complications and functional decline often outweigh the immediate benefits of surgical evacuation[9,20]. Consequently, MMAE emerges as a viable alternative that can be performed under local anesthesia, effectively mitigating the systemic surgical impact for patients otherwise deemed “unfit for surgery”[2,8].

Beyond addressing frailty, MMAE reconciles the tension between clinical necessity and patient autonomy. As a minimally invasive alternative, it functions as an “active bridge” for patients who decline conventional surgery due to the perceived invasiveness of a craniotomy. Furthermore, MMAE maintains a superior safety profile regarding antithrombotic management, as it can often be performed without the complete cessation of antiplatelet or anticoagulant therapy[2]. This capacity to bypass the precarious balance between hemorrhagic and embolic risks is frequently the deciding factor in multidisciplinary consultations[2].

Previous studies have shown variable timelines for complete hematoma resolution after MMAE. Catapano et al[12] reported relatively rapid clearance, with 63% of patients achieving resolution at 3 months and 92% at 6 months, whereas Liu et al[22] observed complete resolution in approximately half of patients, typically requiring 5-6 months and up to 1 year in some cases. For burr-hole evacuation, Chang et al[23] reported a median resolution time of 161 days, with only 47.5% of patients achieving full resolution within 6 months. These discrepancies likely reflect differences in patient populations, hematoma characteristics, and follow-up protocols. Nevertheless, across both surgical and endovascular approaches, most patients achieve clearance within 6 months.

Comparative data support the superiority of MMAE over conventional management. Catapano et al[24] reported complete hematoma resolution in 63% of patients at 3-6 months after MMAE compared with 22% after surgery; additionally, a systematic review and meta-analysis by Sattari et al[14] demonstrated higher rates of complete resolution with MMAE than with conventional treatment (61.9% vs 26.4%; relative risk = 2.01, 95% confidence interval: 1.10-3.68, P = 0.02). This advantage reflects the ability of MMAE to interrupt the vascular supply to fragile neovessels within the hematoma membrane, whereas surgical or conservative approaches primarily evacuate the hematoma without addressing its underlying source.

In our case, bilateral hematomas resolved progressively following MMAE, with the larger right-sided gradational type requiring a longer clearance period than the smaller left-sided homogeneous collection (Figure 3). Established predictors of clearance include baseline hematoma volume, with larger collections resolving more slowly[13,19,22], and internal architecture, as homogeneous and laminar types resolve faster than trabecular or separated types[17,22]. Advanced age also correlates with delayed resolution, and brain re-expansion is often incomplete in those with baseline cerebral atrophy, underscoring the role of patient-related factors[17,22]. Conversely, the type of embolic material used has not been shown to significantly influence resolution rates[13,17,22].

By ensuring robust distal penetration, our refined layered technique effectively targets the neovascular network sustaining hematoma persistence, achieving full clearance and brain re-expansion within three months, even in large symptomatic cases. However, the inherent limitations of a single case report preclude the direct generalizability of these findings to the broader cSDH population. Given the expanding role of MMAE in cSDH management, further technical refinement is warranted. Larger-scale prospective studies or randomized controlled trials are essential to validate this strategy, optimize patient selection, and evaluate long-term safety and efficacy.

CONCLUSION

This case demonstrates standalone MMAE using a refined layered embolization technique as a safe and effective alternative to surgical evacuation, with applicability even in patients with large hematomas and high surgical risk. By enhancing distal targeting while minimizing premature occlusion and reflux, this approach facilitated complete hematoma resolution. Further studies are needed to validate this strategy, define optimal patient selection, and confirm long-term outcomes.