Rescue management of recurrent or growing non-acute subdural hematoma following standalone or adjunctive middle meningeal artery embolization: A case series and systematic review

Abstract

Objective

Recurrent or growing non-acute subdural hematoma (SDH) following standalone or adjunctive middle meningeal artery embolization (MMAe) present a complex clinical challenge. This study aims to investigate the multifactorial causes of recurrence and growing SDH, including vascular and systemic contributors, and explores management strategies to improve outcomes.

Methods

We conducted a retrospective analysis of 22 patients with non-acute SDH requiring rescue treatment after adjunctive or stand-alone MMAe. Patients with documented trauma deemed responsible for the SDH expansion were excluded. Data were collected on patient demographics, clinical presentations, imaging findings, treatment approaches, and outcomes. A systematic review was also conducted across PubMed, Web of Science, Scopus, and Embase databases, adhering to PRISMA guidelines.

Results

Non-traumatic recurrent or growing SDHs were associated with MMA recanalization (27%), contralateral supply from the contralateral MMA (27%), CSF-venous fistulas (5%), and recruitments of vascular collaterals such as deep temporal artery (5%). Management strategies included, respectively, repeat MMAe using polyvinyl alcohol particles, coils, and liquid agents; contralateral MMAe, transvenous embolization for CSF-venous fistulas; and targeted embolization for other vascular contributors. Follow-up assessments were available for 14 patients (64%). Of these, 10 patients (45%) achieved complete resolution of symptoms, three patients (14%) experienced symptomatic improvement, and one patient (5%) had worsening symptoms. In terms of hematoma resolution, nine patients (41%) had complete or near-complete resolution, three patients (14%) exhibited stable hematoma size, and two patients (9%) demonstrated a reduction in hematoma size. Notably, no recurrences were observed after the final treatment. Two patients (9%) died within 10 days of the final embolization treatment due to malignancies.

Conclusion

Recurrent or growing SDHs following MMAe are linked to subdural membrane vascularity and intracranial hypotension which must be investigated and addressed. Treatment of these issues results in high cure rates.

Introductıon

Non-acute subdural hematoma (SDH) is a common and potentially debilitating condition, with an incidence of up to 58/100,000 per year in some populations, and represents a growing public health concern due to population aging. ¹ Traditional SDH treatments include conservative management and surgical evacuation, but recurrence rates can reach 30%, leading to additional hospitalizations and higher healthcare costs.^2,3 The risk is particularly higher in older adults using antithrombotics or those with hematologic malignancies.^4–8

The pathophysiology of SDH involves coagulation, inflammation, and angiogenesis. ⁹ Several studies showed that the middle meningeal artery (MMA) contributes significantly to the vascular supply of SDH membranes, promoting rebleeding and hematoma expansion.^10–12 The first report of MMA embolization (MMAe) in 2000 described complete resolution of refractory SDH. ¹³ Since then, several multicenter series and meta-analyses have shown standalone or adjunctive MMAe reduces recurrence and enables safe resumption of antithrombotics.^14–20 Preliminary results from prospective, randomized trials (EMBOLISE, MAGIC-MT, and STEM) showed that MMAe significantly reduces SDH recurrence or progression with comparable neurological outcomes to surgical treatment.^21,22

Although MMAe is safe and effective, recurrence still occurs in approximately 5% of patients that underwent surgery and adjunctive MMAe. The workup and treatment strategy of this patient population continues to be ill defined. In this study, we first include a literature review of current treatment strategies for addressing these challenging cases, and we then present our institutional experience of patients with persistent, progressive and recurrent SDH after standalone or adjunctive MMAe.

Materıals and Methods

Patient selection and study design

We conducted a retrospective observational case series of 22 consecutive patients with recurrent, persistent, or growing SDH despite prior standalone MMAe or adjunctive MMAe combined with surgical evacuation for non-acute SDHs. The patients were treated and followed between November 2020 and March 2025 at two major medical centers. Eligible patients were identified by reviewing imaging reports through the Radiology department's search engine. The study protocol was approved by the institutional review board (IRB) and informed consent was waived due to retrospective design.

Data collection and study variables

Data were collected on demographics, clinical presentation at recurrence, comorbidities, antithrombotic use, causes of recurrence, prior treatments, details of retreatment, SDH size changes, and follow-up duration. Treatment strategies were guided by multidisciplinary review based on individual patient factors. Recurrent SDH was defined as the reaccumulation or acute rebleeding on CT scan following an initial decrease in SDH size after adjunctive MMAe with surgery. Growing SDH was considered as size increase without prior reduction after standalone MMAe.

Systematic review

Literature search strategy

A systematic review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using PubMed, Web of Science, Scopus, and Embase through 5 April 2025. We used a combination of keywords and Medical Subject Headings (MeSH) terms (“subdural hematoma” AND “middle meningeal artery” AND “embolization” OR “endovascular”) to identify relevant studies on recurrent SDH management following MMAe.

Study selection

Titles and abstracts were screened to exclude irrelevant studies. Full texts of eligible articles were reviewed based on predefined criteria. Inclusion criteria were case reports or series addressing treatment of recurrent SDHs following standalone or adjunctive MMAe. Exclusion criteria included studies without outcome data, inaccessible full text, non-human or unrelated studies, technical notes, reviews, meta-analyses, abstracts, and non-English or editorial/commentary articles.

Results

Literature search results

The comprehensive literature search across four databases yielded 1640 studies. After removing 1031 duplicates, 609 articles were screened. Eight studies met the inclusion criteria and were included in the final analysis (Figure 1).

Figure 1.

PRISMA flow diagram showing the literature review process.

Baseline characteristics of included studies

The characteristics of ten cases of recurrent SDH after failed MMAe in eight studies are summarized in Table 1. Patient ages ranged from 46 to 78 years, with a majority being male (63%). Initial treatment modalities for non-acute SDHs included subdural evacuation port system (SEPS), burr hole irrigation and craniotomy evacuation, with up to three recurrences prior to MMAe. Various embolic materials were utilized, including polyvinyl alcohol (PVA) particles, Onyx, N-butyl cyanoacrylate, embosphere microspheres, and coils. Recurrence after MMAe occurred between one week and three months and was attributed to factors such as organized hematoma with new collateral pathways, contralateral MMA neovascularization, blood supplies from the deep temporal artery or dural arteriovenous fistula (dAVF), brain tumors or metastases, and cerebrospinal fluid (CSF) leakage. Recurrent SDHs were managed through a variety of approaches, including craniotomy evacuation with capsulectomy, contralateral MMAe and burr hole craniostomy. Follow-up ranged from one month to two years, with eight patients achieving complete or near-complete resolution without further recurrence.

Table 1.

Characteristics of ten cases of recurrent SDH after failed MMAe in eight studies.

Study	Country	Study design	Total number of patients	Age (years)	Gender	Comorbidities	Antithrombotic medications	Initial presenting symptoms	Laterality of SDH	Subsequent treatment modalities	Embolic material in the initial MMA embolization	Number of recurrences after initial MMA embolization	Time from MMA embolization to recurrence	Presenting symptoms for recurrent SDH (number)	Reason of recurrence after MMA embolization	Treatment management for recurrent SDH	Embolic material in the subsequent embolization	Clinical outcome at follow-up	Radiological outcome at follow-up	Duration of follow-up
Bhenderu et al., 2023	USA	Case report	2	46	Male	NA	NA	Neck pain and headaches	Bilateral	1st: Bilateral MMA embolization 2nd: Burr hole evacuation and epidural blood patch (final treatment)	NA	1	1 week	Worsening lethargy	CSF leak	Burr hole evacuation and epidural blood patch (3 times)	None	Asymptomatic	Complete resolution, no recurrence	3 months
				78	Female	NA	NA	Headache and retro-orbital pain	Left	1st: Unilateral MMA embolization and mini-craniotomy evacuation 2nd: Craniotomy evacuation and epidural blood patch (final treatment)	NA	1	1 week	Prolonged decreased consciousness	CSF leak	Craniotomy evacuation and epidural blood patch (3 times)	None	Asymptomatic	Complete resolution, no recurrence	1 month
Chihara et al., 2013	Japan	Case report	1	59	Male	Alcoholic liver cirrhosis, pulmonary emphysema, severe thrombocytopenia	NA	Hemiplegia	Left	1st: Burr hole irrigation 2nd: Burr hole irrigation 3rd: Burr hole irrigation and unilateral MMA embolization 4rd: Craniotomy evacuation and capsulectomy (final treatment)	PVA particles (250–355 microns)	1	3 months	None	Organized hematoma and new collateral pathways	Craniotomy evacuation and capsulectomy	None	NA	Complete resolution, no recurrence	2 years
Hubbard et al., 2022	USA	Case report	2	NA	NA	Hypertension	NA	Seizure	Right	1st: Subdural evacuation port system and unilateral MMA embolization 2nd: Contralateral MMA embolization (final treatment)	Onyx	1	2 weeks	Headache	Contralateral MMA neovascularization	Contralateral MMA embolization	PVA particle and coil	Asymptomatic	Near-complete resolution, no recurrence	1 month
				NA	NA	Hypertension	NA	Progressive headache and nausea	Left	1st: Subdural evacuation port system and unilateral MMA embolization 2nd: Craniotomy evacuation and contralateral MMA embolization (final treatment)	Onyx	1	2 weeks	Gait imbalance and confusion	Contralateral MMA neovascularization	Craniotomy evacuation and contralateral MMA embolization	PVA particle and coil	Asymptomatic	Near-complete resolution, no recurrence	6 weeks
Ikeda et al., 2018	Japan	Case report	1	74	Male	Extracranial malignant tumor, pancytopenia	None	Hemiparesis	Left	1st: Burr hole irrigation with drainage 2nd: Burr hole irrigation with drainage 3rd: Burr hole irrigation with drainage and unilateral MMA embolization 4rd: Craniotomy evacuation and capsulectomy (final treatment)	n-BCA	1	6 days	NA	Metastases from the gastric cancer (stage IV adenocarcinoma) to the hematoma capsule	Craniotomy evacuation and capsulectomy	None	NA	NA	NA
Kanazawa et al., 2019	Japan	Case report	1	72	Female	None	NA	Gait disorder and progressive consciousness disturbance	Right	1st: Burr hole drainage 2nd: Craniectomy evacuation 3rd: Craniectomy evacuation 4th: Craniectomy evacuation and bilateral MMA embolization (final treatment)	n-BCA and coil	1	NA	NA	Angiosarcoma originating from the skull	No additional treatment due to progressive deterioration	None	Patient died 16 days after the first surgery	NA	NA
Kulhari et al., 2023	USA	Case report	1	57	Female	Ulnar vein thrombosis, hypertension, hypothyroidism	Rivaroxaban	Worsening headaches	Left	1st: Unilateral MMA embolization 2nd: Embolization of deep temporal artery (final treatment)	Embosphere Microspheres (100–300 microns)	1	1 month	NA	Blood supply from prominent deep temporal artery	Embolization of deep temporal artery	Embosphere Microspheres (100–300 microns)	Asymptomatic	Complete resolution, no recurrence	6 months
Rutledge et al., 2021	USA	Case report	1	50s	Male	NA	NA	Headaches	Left	1st: Unilateral MMA embolization 2nd: Contralateral MMA embolization (final treatment)	Coil	1	1 month	None	Blood supply from contralateral MMA	Contralateral MMA embolization	Liquid embolic agent	NA	Near-complete resolution, no recurrence	3 months
Shotar et al., 2021	France	Case report	1	64	Male	Alcohol abuse, Lewy body dementia, and pulmonary embolism	NA	NA	Bilateral	1st: Bilateral burr hole craniostomy and bilateral MMA embolization 2nd: Burr hole craniostomy (final treatment)	Embosphere Microspheres (300–500 microns)	1	3 months	Gait disturbance and confusion	Dural arteriovenous fistula of superior sagittal sinus	Burr hole craniostomy	None	NA	Complete resolution, no recurrence	3 months

Case series

A total of 195 patients underwent standalone or adjunctive MMAe for treatment of SDH in our institute between November 2022 and March 2025. This retrospective case series focused on 22 patients with recurrent SDH despite undergoing MMAe. The cohort comprised 14 males and 8 females, with an mean age of 74.5 ± 9.8 years (range: 54–91). All patients had various comorbidities, including cardiovascular diseases, diabetes mellitus, pancytopenia, and malignancies. At first presentation, about half of the patients were on antiplatelet or antithrombotic therapy. In detail, six patients (27%) were taking 81 mg aspirin alone, one patient (5%) was on a combination of 81 mg aspirin and 5 mg Apixaban, one patient (5%) on 81 mg aspirin and 10 mg Xarelto, one patient (5%) on 5 mg Apixaban alone, and one patient (5%) on 10 mg Xarelto alone. Clinical presentations included altered mental status, headaches, frequent falls, dizziness, and extremity weakness. Eleven patients (50%) presented with unilateral SDHs, while 11 (50%) had bilateral convexity hematomas. Initial management strategies involved standalone MMAe in 10 patients (45%) and adjunctive MMAe combined with surgical interventions including SEPS drain placement in 12 patients (55%). Standalone MMAe was performed in patients with small SDH (<15 mm) and mild symptoms such as headaches. In the initial MMAe procedures at presentation, PVA particles were the sole embolic material used in 12 patients (55%), a combination of PVA particles and coils was used in eight patients (36%), coils alone in one patient (5%), and Onyx alone in one patient (5%) (Table 2).

Table 2.

Characteristics of 22 cases of recurrent SDH after failed MMAe.

Age (years)	Gender	Comorbidities	Antithrombotic medications	Initial presenting symptoms	Laterality of SDH	Subsequent treatment modalities	Embolic material in the initial MMA embolization	Number of recurrences after initial MMA embolization	Time from initial MMA embolization to recurrence	Presenting symptoms for recurrent SDH (number)	Reason of recurrence after MMA embolization	Embolic material in the subsequent embolization	Clinical outcome at last follow-up	Radiological outcome at follow-up	Follow-up time
83	Male	Acute myeloblastic leukemia, hypertension, hyperlipidemia, chronic kidney disease	None	Frequent falls	Right	1st: Unilateral MMAe 2nd: Unilateral burr hole evacuation with drainage 3rd: Unilateral MMAe (Final treatment)	PVA particle (150–250 microns) and coil	2	4 weeks	Persistent falls and left lower weakness	Recanalization of MMA	PVA particle (150–250 microns) and coil	Patient died 10 days after treatment for recurrent SDH due to relapsed recurrent AML	NA	NA
86	Male	Hypertension, hyperlipidemia, heart failure, coronary artery disease, atrial fibrillation, chronic kidney disease	Aspirin 81 mg	Frequent falls, lightheadedness, left sided weakness	Right	1st: Unilateral MMAe and Unilateral SEPS 2nd: Contralateral MMAe (Final treatment)	PVA particle (150–250 microns) and coil	1	4 weeks	None	Blood supply from contralateral MMA	PVA particle (150–250 microns) and coil	Resolution of symptoms	Complete resolution	4 months
79	Male	Coronary artery disease, atrial fibrillation, myocardial infarction	Aspirin 81 mg and Apixaban 5 mg	Headache	Bilateral	1st: Bilateral burr hole evacuation with drainage and bilateral MMAe 2nd: Left MMAe and left mini craniotomy evacuation with drainage (Final treatment)	Coils	1	8 weeks	Severe headache	Recanalization of left MMA	PVA particle (150–250 microns) and coil	NA	NA	NA
65	Male	Coronary artery disease, atrial fibrillation, myocardial infarction, NK/T cell lymphoma, pancytopenia	Apixaban 5 mg	Dizziness	Right	1st: Unilateral MMAe 2nd: Embolization of deep temporal artery and burr hole evacuation (Final treatment)	PVA particle (150–250 microns)	1	3 weeks	None	Blood supply from deep temporal artery	PVA particle (150–250 microns)	Patient died 1 day after treatment for recurrent SDH due to respiratory distress and acute progressive metabolic acidosis	NA	NA
55	Female	Parkinson's disease	None	Severe headache	Right	1st: Unilateral minicraniotomy evacuation with drainage and MMAe 2nd: Unilateral minicraniotomy evacuation with drainage and contralateral MMAe (Final treatment)	PVA particle (150–250 microns)	1	1 week	Increasing headache with nausea	Blood supply from contralateral MMA	PVA particle (150–250 microns) and coil	Improvement in symptoms	Near-complete resolution	2 months
69	Male	Hypertension, hyperlipidemia, diabetes mellitus, hepatocellular carcinoma, chronic hepatitis C, persistent encephalopathy, hypothyroidism, chronic kidney disease	None	Altered mental status	Bilateral	1st: Bilateral MMAe 2nd: Left MMAe (Final treatment)	PVA particle (150–250 microns)	1	3 weeks	None	Recanalization of left MMA	Coil	NA	NA	NA
63	Male	Hypertension, hyperlipidemia, diabetes mellitus, hypothyroidism	None	Headache	Right	1st: Unilateral MMAe and SEPS 2nd treatment: Right craniotomy evacuation without drainage and bilateral MMA embolization 3rd: CSF-venous fistula embolization (Final treatment)	1st MMAe: Onyx 18 2nd MMAe: PVA particle (150–250 microns)	2	2 weeks	Worsening headache, left sided numbness and weakness	Cerebrospinal fluid venous fistula	Onyx 18	Resolution of symptoms	Near-complete resolution	1 month
76	Male	Hypertension, dyslipidemia, coronary artery disease, atrial fibrillation, aortic valve regurgitation	Aspirin 81 mg and Xarelto 10 mg	Headache, difficulty walking	Bilateral	1st: Bilateral MMAe and left SEPS 2nd: Left MMAe (Final treatment)	PVA particle (150–250 microns)	1	10 weeks	None	Recanalization of left MMA	PVA particle (250–355 microns) and coil	Resolution of symptoms	Interval decrease in size	3 month
83	Male	Hypertension, hyperlipidemia, heart failure	Aspirin 81 mg	Headache	Bilateral	1st: Left craniotomy and left MMAe 2nd: Bilateral MMAe (Final treatment)	PVA particle (45–150 microns)	1	8 weeks	Right side weakness and word finding difficulty	Recanalization of left MMA	PVA particle (150–250 microns)	Resolution of symptoms	Stable in size	5 months
68	Male	Monoclonal B-cell lymphocytosis	None	Headache	Right	1st: Unilateral MMAe 2nd: Right side burr hole evacuation, left side MMAe, right side ADT artery and STA embolization	PVA particle (150–250 microns)	1	3 weeks	Worsening left lower extremity weakness, ongoing right-side headaches	Blood supply from contralateral MMA, anterior deep temporal (ADT) artery and superficial temporal artery (STA)	Embosphere particle (100–300 microns) and Onyx 18	NA	NA	NA
83	Female	Hypertension, aortic valve sclerosis, hyperlipidemia, diabetes, hyperthyroidism, chronic hepatitis C, glaucoma, dementia, epilepsy	Aspirin 81 mg	Frequent falls	Left	1st: Unilateral burr hole evacuation without drainage and MMAe 2nd: Bilateral MMAe (Final treatment)	PVA particle (150–250 microns)	1	12 weeks	Frequent falls	Blood supply from contralateral MMA	PVA particle (150–250 microns)	Resolution of symptoms	Complete resolution	4 months
75	Male	Hypertension, hyperlipidemia, coronary artery disease, chronic hepatitis C, end stage liver disease, chronic thrombocytopenia and coagulopathy, recurrent bladder cancer	None	Headache	Left	1st: Unilateral MMAe 2nd: Contralateral MMAe (Final treatment)	PVA particle (150–250 microns)	1	10 weeks	Altered mental status	Blood supply from contralateral MMA	PVA particle (150–250 microns)	Improvement in symptoms	Stable in size	2 weeks
54	Female	Hypertension, atrial fibrillation, hypothyroidism, dementia	Xarelto 10 mg	Headache	Bilateral	1st: Bilateral burr hole evacuation without drainage and bilateral MMAe 2nd: Right MMAe (Final treatment)	PVA particle (150–250 microns)	1	3 weeks	Worsening headache	Recanalization of right MMA	PVA particle (150–250 microns) and coil	Resolution of symptoms	Near-complete resolution	6 weeks
74	Female	Obstructive hydrocephalus	None	Headache and imbalance	Right	1st: Unilateral MMAe 2nd: Right craniotomy evacuation with drainage (Final treatment)	PVA particle (150–250 microns) and coil	1	3 weeks	None	NA	NA	Improvement in symptoms	Near-complete resolution	1 month
81	Female	Hypertension, hyperlipidemia, hypothrodisim, cervical spondylosis	None	Headache, dizziness, falls	Bilateral	1st: Bilateral MMAe 2nd: Bilateral burr hole with drainage (Final treatment)	PVA particle (150–250 microns) and coil	1	3 weeks	Worsening headache	NA	NA	Improvement in symptoms	Complete resolution	4 months
71	Male	Hypertension, dyslipidemia, coronary artery disease, lung adenocarcinoma	Aspirin 81 mg	Right lower extremity weakness	Bilateral	1st: Bilateral MMAe and SEPS 2nd: Right burr hole without drainage (Final treatment)	PVA particle (150–250 microns)	1	2 weeks	None	NA	NA	Resolution of symptoms	Interval decrease in size	2 weeks
64	Female	Hypertension, hyperlipidemia, diabetes, alcoholic cirrhosis, encephalopathy, pancytopenia	None	Confusion	Left	1st: Unilateral MMAe 2nd: Left cranioctomy with drainage (Final treatment)	PVA particle (150–250 microns)	1	4 weeks	Altered mental status, right-sided weakness	NA	NA	Resolution of symptoms	Complete resolution	2 months
77	Male	Hyperlipidemia	Aspirin 81 mg	Frequent falls, right sided weakness	Bilateral	1st: Bilateral MMAe and right burr hole with drainage 2nd: Left burr hole with drainage (Final treatment)	PVA particle (150–250 microns) and coil	1	4 weeks	None	NA	NA	Resolution of symptoms	Near-complete resolution	6 months
79	Female	Hypertension, hyperlipidemia, obstructive sleep apnea	Aspirin 81 mg	Right hand discoordination, memory difficulty, unsteadiness	Bilateral	1st: Bilateral MMAe and burr hole with drainage 2nd: Right mini-cranioctomy	PVA particle (150–250 microns) and coil	1	4 weeks	Left sided weakness	NA	NA	NA	NA	NA
78	Male	Hypertension, hyperlipidemia, obesity	None	Headache	Bilateral	1st: Bilateral MMAe 2nd: Bilateral burr hole with drainage (Final treatment)	PVA particle (150–250 microns) and coil	1	3 weeks	Headache, dizziness, gait imbalance	NA	NA	NA	NA	NA
91	Female	Hypertension, chronic kidney disease, diabetes, asthma	None	Generalized weakness and frequent falls	Left	1st: Unilateral MMAe and burr hole evacuation with drainage 2nd: Contralateral MMAe (Final treatment)	PVA particle (300–500 microns)	1	2 weeks	Altered mental status, gait imbalance, falls	Blood supply from contralateral MMA	Coil	Worsening mental status	Stable in size	3 weeks
84	Male	Hypertension, hyperlipidemia, diabetes	None	Frequent falls, headache	Bilateral	1st: Bilateral MMAe 2nd: Bilateral burr hole with drainage (Final treatment)	PVA particle (150–250 microns) and coil	1	4 weeks	Worsening headache, dizziness, gait imbalance	NA	NA	NA	NA	NA

Recurrent or growing SDHs, with or without new or worsening symptoms, occurred at a mean interval of 4.5 ± 3.0 weeks after the initial MMAe. Fourteen patients (64%) presented with symptoms of recurrent hematoma, including worsening headache, dizziness, extremity numbness and weakness, altered mental status, frequent falls, or word-finding difficulties. All patients exhibited increased hematoma size on follow-up CT scan, confirming recurrence or growing. Angiography demonstrated recanalization of embolized MMA branches in six patients (27%), contralateral MMA supply of SDH membranes in six patients (27%), collateralization from the deep temporal artery in one patient (5%), and CSF-venous fistula in one patient (5%). Two patients (9%) experienced two recurrences following initial MMAe. In one case, the patient was initially treated with standalone MMAe using PVA particles, but was found to have worsening symptoms and a growing SDH and burr hole evacuation was performed. Following a second recurrence, the patient underwent repeat standalone MMAe using both PVA particle and coil. In the other case, the patient initially underwent SEPS drainage along with adjunctive MMAe using Onyx, and upon significant recurrence of the SDH underwent craniotomy evacuation and a second adjunctive MMAe using PVA particles. After the second recurrence, patient underwent CSF-venous fistula embolization as the final treatment. Among 14 patients (64%) requiring repeat embolization in the final treatment, a combination of PVA particles and coils were utilized in six patients (27%), PVA particles alone in four patients (18%), coils alone in two patients (9%), Onyx 18 alone in one patient (5%), and a combination of Embosphere particle and Onyx 18 in one patient (5%). Additionally, rescue craniotomy was performed in two standalone (9%) and four adjunctive MMAe cases (18%), while rescue burr hole evacuation was employed in seven standalone (33%) and two adjunctive MMAe cases (9%). Of the 22 patients in our case series, two patients (9%) died during hospitalization due to severe comorbidities and complications unrelated to the procedures and SDH. An additional six patients (27%) were lost to follow-up, with no available clinical or radiological data. For the remaining 14 patients (64%), the mean follow-up duration was 2.5 ± 1.8 months. At the last follow-up, clinical outcomes revealed that nine patients (41%) experienced complete symptom resolution, four patients (18%) showed symptomatic improvement, and one patient (5%) had worsening mental status. Follow-up CT scans showed complete or near-complete hematoma resolution in nine patients (41%). While SDH size remained stable in three patients (14%), an interval decrease in hematoma size was observed in two patients (9%). No further recurrences were observed in any patient following the final treatment.

Illustrative cases

Case 1

A 63-year-old male with a medical history of hypertension, hyperlipidemia, diabetes mellitus, and hypothyroidism presented with a 5-day history of persistent headaches. Non-contrast CT scan revealed a right holohemispheric non-acute SDH measuring 12 mm in thickness, with a hyperdense component and a 10 mm leftward midline shift (MLS). The SDH caused significant mass effect, including effacement of the body, atria, and occipital horn of the right lateral ventricle. The patient underwent right-sided evacuation with SEPS (Medtronic, Minnesota, USA), followed by right MMAe with Onyx 18 (Medtronic, Minnesota, USA). The patient was discharged three days later with improvement in both hematoma size and MLS, which was reduced to 6 mm on postoperative CT scan.

Two weeks later, the patient returned with worsening right-sided headaches and gait instability. Repeat CT scan showed reaccumulation of the right-sided SDH measuring 15 mm with an increased leftward MLS to 12 mm. Selective angiography of the right MMA demonstrated recanalization of the central MMA branches supplying the hypervascular SDH. Selective angiography of the left MMA also revealed crossover of distal branches supplying the right dural membranes. The patient underwent right-sided craniotomy evacuation followed by bilateral MMAe using PVA particles (Contour 150–250, Boston Scientific, Marlborough, USA). The patient was discharged after four days with improvement in hematoma size to 8 mm and MLS to 6 mm on postoperative image.

One week after discharge, the patient presented with new-onset left hemibody numbness, tingling, and weakness. CT scan revealed a recurrence of the right SDH measuring 13 mm with an increased leftward MLS to 10 mm. Given the repeated recurrence despite prior treatments, a CSF leak was considered as a potential contributing factor. Total spine MRI revealed no evidence of an extradural collection or definite spinal CSF leak; however, brain MRI showed subtle findings, including a reduced mammillopontine interval and anterior displacement of the pons, suggestive of intracranial hypotension. A lateral decubitus dynamic CT myelogram encompassing the entire spine identified a CSF-venous fistula at the right T4-T5 neural foramen. Transvenous embolization of the right T4-T5 and T3-T4 neural foraminal veins, paraspinal veins, and the epidural venous plexus was performed using Onyx 18. The procedure was completed without complications, and the patient was discharged five days later in stable condition. At the one-month follow-up, the patient reported complete resolution of symptoms, including headache and neurological deficits. Additionally, follow-up CT scan demonstrated significant improvement, with the right SDH measuring 3 mm and complete resolution of the MLS (Figures 2 and 3).

Figure 2.

(A) Axial CT scan at initial presentation showing a right holohemispheric mixed-density SDH and leftward MLS. (B) Axial CT scan after SEPS drain placement, showing reduction in SDH size and MLS. (C) Selective ECA angiography prior to embolization demonstrating prominent branches of the MMA. (D) Selective MMA angiography after embolization with Onyx 18, showing occlusion of the distal branches. (E) Axial CT scan at the first recurrence, revealing reaccumulation of the right SDH with increased leftward MLS. (F) Postoperative axial CT scan following right-sided craniotomy evacuation, demonstrating reduction in SDH size and MLS. (G) Selective angiography of the right MMA showing recanalized central branches supplying the SDH membranes. (H) Selective angiography of the right MMA after embolization with PVA particles (Contour 150–250), demonstrating distal occlusion of recanalized branches.

Figure 3.

(A) Selective left MMA angiography demonstrating crossover of distal branches supplying the right dural membranes. (B) Selective left MMA angiography after embolization with PVA particles (Contour 150–250), showing occlusion of collateral branches. (C) Axial CT scan at the second recurrence, showing reaccumulation of the right SDH with increased leftward MLS. (D-E) Lateral decubitus spine CT myelogram revealing contrast filling (white arrows) at the level of the right T4-T5 neural foramen. (F) Anterior-posterior and (G) lateral X-rays after trans-venous embolization showing onyx cast and closure of the CSF-venous fistula. (H) Axial CT scan at one-month follow-up, demonstrating near-complete resolution of the right SDH with no remaining the MLS.

Case 2

A 83-year-old male with a history of acute myeloblastic leukemia (AML), hypertension, hyperlipidemia, and chronic kidney disease presented with frequent falls. Non-contrast CT scan revealed a right frontoparietal chronic SDH measuring up to 9 mm in thickness with associated mass effect, resulting in a 7 mm leftward MLS. Selective angiography of the right MMA identified the prominent anterior and posterior branches with a meningo-lacrimal branch originating from the anterior division of the MMA at the level of the sphenoid ridge and traveling to the orbit. A microcatheter was navigated distal to this branch, and the anterior and posterior divisions of the MMA were embolized using PVA particles (Contour 150–250), followed by coil embolization of the proximal MMA just past its entry into the foramen spinosum. The procedure was completed without complications, and the patient was discharged in stable neurological condition.

One month later, the patient returned with persistent falls and left lower extremity weakness. A repeat CT scan showed a growing SDH measuring up to 26 mm with an increasing leftward MLS of 12 mm. The patient underwent a burr hole evacuation without drainage, which resulted in a reduction in SDH size of 11 mm and leftward MLS of 8 mm. However, the patient required a prolonged 14-day hospital stay due to chemotherapy and daily platelet transfusions. Two weeks after discharge, the patient underwent repeat CT scan due to ongoing concerns of re-bleeding and persistent transfusion needs. The scan showed a second growing SDH measuring 26 mm and leftward MLS of 11 mm. Selective angiography of the right MMA revealed persistent flow past the previously placed coils, with normal-appearing anterior and posterior divisions of the MMA. The meningo-lacrimal branch traveling into the orbit and terminating in the superolateral region without associated choroidal blush was again identified. This branch was embolized with a coil, and both anterior and posterior MMA divisions were embolized using PVA particles (Contour 150–250). Post-embolization angiography confirmed complete occlusion of the distal branches of both MMA divisions and the meningo-lacrimal branch. Despite successful embolization, the patient's recurrent AML, persistent pancytopenia and transfusion-refractory thrombocytopenia persisted. Given the lack of response to platelet transfusions and worsening clinical condition, after discussions with the family and care team, a transition to comfort-focused care was decided. The patient died 10 days after the embolization procedure (Figures 4 and 5).

Figure 4.

(A) Axial CT scan at initial presentation showing a right frontoparietal chronic SDH and leftward MLS. (B) Lateral and (C) anterior-posterior selective right MMA angiography prior to embolization demonstrating the anterior and posterior divisions of the MMA and a meningo-lacrimal branch (white arrows) originating from the anterior division of the MMA at the level of the sphenoid ridge. (D) Lateral and (E) anterior-posterior selective right MMA angiography after embolization with PVA particles (Contour 150–250), showing occlusion of the distal branches of the MMA while preserving the meningo-lacrimal branch. (F) Lateral and (G) anterior-posterior selective common carotid artery (CCA) angiography illustrating the location of the coil (black arrows) at the proximal MMA just past its entry into the foramen spinosum. (H) Axial CT scan at first recurrence revealing reaccumulation of the right SDH with increased leftward MLS.

Figure 5.

(A) Postoperative axial CT scan following burr hole evacuation procedure showing reduction in right SDH size with decreased leftward MLS. (B) Axial CT scan at second recurrence demonstrating reaccumulation of the right holohemispheric SDH with increased leftward MLS. (C) Lateral and (D) anterior-posterior selective right MMA angiography prior embolization revealing persistent flow past previously placed coils (black arrows) and visualization of the meningo-lacrimal branch (white arrows) without associated choroidal blush. (E) Lateral and (F) anterior-posterior selective right ECA angiography demonstrating successful occlusion of the MMA branches using PVA particles (Contour 150–250) and additional coils (black arrows).

Case 3

A 55-year-old female with a history of Parkinson's disease and prior deep brain stimulation presented with three days of severe headaches and two episodes of emesis. Non-contrast CT scan revealed a right holohemispheric chronic SDH measuring up to 11 mm in thickness with a small acute component, associated with mass effect causing a 10 mm leftward MLS. Initial treatment included a right craniotomy for SDH evacuation with drain placement, followed by right MMAe with PVA particles (Contour 150–250). Postoperative CT scan showed a reduction in SDH size to 7 mm and an improvement in the MLS to 4 mm. The postoperative course was uneventful, and the patient was discharged five days later in stable condition.

One week later, the patient returned with worsening headaches and nausea. Repeat CT scan demonstrated reaccumulation of the right SDH measuring up to 16 mm, with new acute blood products and an increased leftward MLS of 13 mm. The patient underwent a right minicraniotomy for SDH evacuation with drain placement. Following the surgery, selective angiography of the right external carotid artery (ECA) and MMA showed complete occlusion of the right MMA. Subsequent angiography of the left MMA identified multiple branches crossing the midline, filling the most distal branches of the right MMA and supplying the right SDH membranes. Embolization of the frontal and parietal branches of the left MMA was performed using PVA particles (Contour 150–250). Additionally, a coil was placed proximally, and the petrosquamosal branch was also embolized with PVA particles (Contour 150–250). The procedures were completed without complications and postoperative CT scan demonstrated a reduction in the size of the right SDH to 10 mm and an improvement in the MLS to 7 mm. The patient was discharged six days later in stable condition. At the two-month follow-up, symptoms related to SDH were completely resolved and CT scan demonstrated significant improvement, with the SDH reduced to 3 mm and complete resolution of the MLS (Figures 6 and 7).

Figure 6.

(A) Axial CT scan at initial presentation showing a right chronic SDH and leftward MLS with bifrontal deep brain stimulator electrode leads (white arrows) terminating in the region of the subthalamic nuclei. (B) Postoperative axial CT scan following right craniotomy evacuation, showing reduced SDH size and MLS. (C) Lateral and (D) anterior-posterior selective angiography of the right MMA prior to embolization, showing prominent branches of the MMA (E) Lateral and (F) anterior-posterior selective angiography of the right MMA after embolization with PVA particles (Contour 150–250), demonstrating distal occlusion of the MMA branches. (G) Axial CT scan at first recurrence showing increased SDH size and MLS (H) Postoperative axial CT scan following right mini-craniotomy evacuation for recurrent SDH, showing improvement in SDH size and MLS.

Figure 7.

(A) Lateral and (B) anterior-posterior selective left MMA angiography prior to embolization revealing distal branches (white arrows) extending contralaterally across the midline to supply the right dural membranes. (C) Lateral and (D) anterior-posterior left CCA angiography after embolization of the MMA with PVA particles (Contour 150–250) and a coil (black arrows), showing complete occlusion of the MMA main trunk and branches (E) Axial and (F) coronal CT scan at two-month follow-up demonstrating nearcomplete resolution of the right SDH and the absence of MLS.

Dıscussıon

SDH arises from the disruption of fragile bridging veins crossing the subdural space, often following minor trauma or in patients with risk factors such as advanced age, antithrombotic therapy, or coagulopathy. The hematoma triggers inflammation, neovascularization, and formation of fragile membranes, promoting recurrent bleeding.^23,24 MMAe targets these hypervascular membranes responsible for ongoing hematoma growth. ²⁵ By reducing their blood supply, MMAe helps mitigate rebleeding and facilitates hematoma resolution. Despite its effectiveness, MMAe is not without limitations and certain challenges persist. Recanalization of embolized MMA branches, contralateral supply from the opposing MMA, and intracranial hypotension such as in ventriculoperitoneal shunt overdrainage have been implicated in recurrent or growing hematomas. Moreover, comorbidities such as leukemia, thrombocytopenia, and the use of antithrombotic drugs, further compound the risk of recurrence. Our study demonstrates these multifactorial causes of recurrent or growing hematomas in patients undergoing MMAe and presents workup and treatment strategies addressing these challenges.

The efficacy of MMAe is likely influenced by the embolic material and penetration depth. Liquid embolics are more likely to achieve a deeper penetration, but the distal penetration can be prevented by challenges in navigating branches of the MMA (such as the anterior or frontal branch through the sphenoid wing) away from dangerous anastomosis. However, clinical studies have yielded less conclusive results regarding the superiority of liquid embolics over particles. A multicenter analysis comparing Onyx, PVA particles, and n-BCA found no significant differences in radiological improvement, surgical rescue rates, or major complications among these agents. ²⁶ Similarly, a separate study comparing Onyx and PVA particles reported equivalent embolization failure rates and surgical rescue outcomes, although late follow-up CT scans showed a greater reduction in hematoma thickness in the PVA particle group. ²⁷ Coils, either alone or in combination with particles, have also shown promise, with a study reporting that standalone coil embolization was sufficient to prevent recurrence. ²⁸ Another study found no differences in surgical rescue rates or hematoma volume reduction when comparing coil-only embolization to PVA particle and coil combination. ²⁹ A recent study showed that aggressive embolization targeting both frontal and parietal MMA branches with distal penetration yielded lower surgical rescue rate compared to nonaggressive penetration with proximal coiling and nonaggressive penetration alone. ³⁰ In our study, we observed recanalization of previously embolized branches with PVA, and we even identified a case involving PVA particles plus proximal coiling with recanalization of the main MMA trunk and branches after few weeks, necessitating a more aggressive second embolization using additional coils and particles. Despite these studies, there is no consensus on the optimal embolic material or technique. Although ongoing trials continue to explore safety and efficacy, further randomized studies comparing liquid embolics and PVA particles are needed to guide technique and material selection.

While unilateral MMAe is effective for treating unilateral SDH, recurrent or growing hematomas may still occur due to alternative vascular supply. In such cases, the contralateral MMA can play a significant role in maintaining the vascular supply to the affected dura. Lam et al. reported a refractory chronic SDH where recurrence occurred despite two surgical treatments. ³¹ Selective angiography revealed that the parasagittal region of the hematoma was supplied by the contralateral MMA, prompting bilateral MMAe and midline craniotomy evacuation. Follow-up CT scan demonstrated complete hematoma resolution. Similarly, in our study, contralateral angiography in cases of recurrent non-acute SDH after unilateral MMAe demonstrated robust vascular supply from the contralateral MMA. These cases were successfully addressed by contralateral MMA embolization that resulted in a more extensive and definitive devascularization of subdural membranes. This observation raises the question for the need of upfront bilateral embolization in unilateral SDH cases to reduce the recurrence risk. Further prospective studies are needed to compare unilateral versus bilateral MMAe in patients with unilateral SDH, especially for determining its potential advantages in hematoma resolution and recurrence prevention despite increased costs and higher exposure to complications.

CSF-venous fistulas arise from abnormal communications between the spinal subarachnoid space and adjacent paraspinal veins.^32,33 These fistulas are an underrecognized cause of spontaneous intracranial hypotension (SIH), frequently presenting with orthostatic headaches.^34,35 Diagnosis often requires advanced imaging such as lateral decubitus digital subtraction myelography. ³⁶ Transvenous Onyx embolization has recently demonstrated high efficacy and safety by sealing the aberrant venous connections. ³⁷ However, diagnosis may be delayed in the absence of typical SIH symptoms, as observed in one of our cases, where a CSF-venous fistula led to recurrent SDH despite multiple MMAe. Ultimately, transvenous embolization resolved the fistula and prevented further recurrence. Similarly, Madhavan et al. reported four cases of combined SDH and CSF-venous fistula treated with concurrent MMAe and transvenous Onyx embolization in a single session, demonstrating the necessity of addressing both pathologies to prevent recurrence. ³⁸ dAVFs represent another pathological vascular connection associated with SDH recurrence. Yajima et al. reported a case of refractory SDH caused by dAVF, treated successfully with n-BCA embolization, resulting in complete resolution of both dAVF and SDH on follow-up imaging. ³⁹

This study has several limitations. First, the retrospective design inherently introduces risks of selection bias and unmeasured confounding variables. Second, the treatment approaches were not standardized and varied based on institutional and operator preferences, which may contribute to selection bias. Third, although we included consecutive patients from two centers, the sample size remains relatively small and may limit generalizability. Lastly, follow-up imaging and clinical assessments were not uniformly available for all patients, with 36% lost to follow-up, which may have introduced attrition bias and affected the robustness of outcome analysis. These factors underscore the need for prospective studies with standardized protocols and longer follow-up to validate our findings.

Conclusıon

Recurrent or growing SDHs following MMAe are linked to subdural membrane vascularity and intracranial hypotension which must be investigated and addressed. While MMAe effectively reduces recurrence and promotes hematoma regression, optimal outcomes require tailored approaches incorporating aggressive embolization techniques, contralateral MMA evaluation, and management of underlying systemic and anatomical contributors. Advanced imaging and novel therapies, such as transvenous embolization of CSF-venous fistulas, play an increasingly important role. Further studies comparing different embolic materials, bilateral versus unilateral MMAe in patients with unilateral SDH, and multimodal strategies are needed to refine management in complex cases. A comprehensive, individualized approach remains essential to reduce recurrence and improve outcomes in this challenging population.