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Abstract
Background This study quantifies the impact of middle meningeal artery embolization (MMAE) for subdural hematomas (SDHs) by estimating a target population.
Methods A population-based study at a tertiary hospital, the main SDH facility for a four-county population, used primary ICD-10 codes over 3 years to collate SDH hospitalizations. Clinical and imaging data confirmed traumatic versus non-traumatic and acute versus non-acute (mixed or chronic) SDH. The MMAE-eligible population included patients with non-traumatic, non-acute SDH aged ≥18 years plus patients with ‘traumatic’ but non-acute SDH aged ≥60 years presenting with a fall. This was contrasted with the rate of large vessel strokes in the same population.
Results 1279 hospitalizations with a primary ICD-10 SDH diagnosis were identified, with 389 from the study population. Excluding repeat admissions, 350 patients were analyzed, 233 (67%) traumatic, and 117 (33%) non-traumatic SDH. Regarding etiology, ‘fall ≥60 years’ was the most common category in the entire cohort (n=156; 45% (95% CI 39% to 50%)). The SDH rate was 52/100 000 persons/year (95% CI 47 to 57). The rate of all non-traumatic, non-acute SDH in patients aged ≥18 years was 17/100 000 persons/year (95% CI 15 to 20), combining with ‘traumatic’ but non-acute fall-related SDH in patients aged ≥60 years yielded 41/100 000 persons/year (95% CI 36 to 47). This demographic may represent an MMAE-eligible population, exceeding large vessel stroke rates (31/100 000 persons/year) in the same population, estimating 139 387 potential MMAE cases/year (95% CI 121 517 to 158 168) in the USA.
Conclusion MMAE could transform non-acute SDH management, especially in the elderly, potentially surpassing the impact of large vessel stroke. Clinical trials are essential for validation of its efficacy and safety compared with standard management.
- Subdural
- Hemorrhage
- Embolic
- Meninges
- Statistics
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
Previous research has outlined the incidence of chronic subdural hematomas. These studies, however, precede the advent of middle meningeal artery embolization (MMAE) as a treatment option.
WHAT THIS STUDY ADDS
This study approaches the epidemiology of subdural hematomas in the setting of MMAE, aiming to identify a population that could be eligible for this procedure.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
With several randomized clinical trials nearing completion and showing promising preliminary results, analyzing population data in the context of MMAE is important. This could inform the development of care systems for managing this debilitating condition, particularly among elderly patients.
Introduction
According to the US Census Bureau (https://www.census.gov), age 65 and over is the fastest growing segment of the US population, with a growth rate five times faster than the entire population from 1920 to 2020 (https://www.census.gov/library/stories/2023/05/2020-census-united-states-older-population-grew.html). At almost 58 million, the ≥65 age group represents just over 17% of the US population. Chronic subdural hematoma (SDH) is the most common neurosurgical condition in this age group,1 and is often a cause of progressive decline in physical and cognitive health. In fact, a chronic SDH has been categorized as a sentinel health event in the elderly2 3 leading to increased mortality rates in patients with chronic SDH relative to standardized mortality data. The incidence and prevalence of chronic SDH have been increasing in recent years, reflecting the trends of the aging demographic,4 with the highest rates observed in individuals aged >70 years. Studies have reported an annual incidence ranging from 1.72 to 18.8 cases per 100 000 person-years in the general population.5 6 However, in older people, much higher rates have been reported ranging from 58/100 000 persons/year5 to 80/100 000 persons/year7 in people aged >65 years and 127/100 000 persons/year in those aged >80 years.7 The prevalence of chronic SDH has been estimated to be approximately 58–86 cases per 100 000 population,6 and it is more common in men than in women with a male-to-female ratio ranging from 2:1 to 4:1.8 9
Several risk factors have been associated with the development of chronic SDH, the most recognized being head trauma, even minor trauma, and ground level falls which account for a significant proportion of chronic SDH cases. Other risk factors include alcohol abuse, coagulopathy (eg, use of anticoagulant or antiplatelet medications), seizure disorders, hypertension, liver disease, and certain medications.3 5 Although chronic SDH is generally considered a treatable condition, it can lead to significant morbidity and mortality, especially if managed inadequately. Recurrence of chronic SDH is not uncommon. Studies have reported recurrence rates ranging from 5% to 30% after initial treatment. Factors associated with an increased risk of recurrence include advanced age, bilateral chronic SDH, larger hematoma size, and certain radiological findings.10 11 The mortality rate associated with chronic SDH ranges from 4% to 30%.12 Furthermore, chronic SDH can cause a wide range of neurological deficits and impairments in cognitive function, gait, balance, and activities of daily living.9
Preliminary results from some randomized clinical trials indicate favorable efficacy of middle meningeal artery embolization (MMAE) versus standard management for the treatment of chronic SDH.13–15 If the final results of multiple concluding trials are positive, MMAE will be added to the treatment paradigm for chronic SDH. The purpose of this study is to define the scope of MMAE by identifying a target population that could benefit from this procedure.
Methods
Defining the study population
The study design adheres to previously established methodology for population-based analyses.16 17 Three crucial parameters were considered: a clearly demarcated population, sufficient accessibility to accurately estimate disease burden, and reliable disease markers. The target population for this study encompassed four counties constituting the primary service area of a large tertiary referral hospital, equipped with a level 1 trauma center and a comprehensive stroke facility. Initially, International Classification of Disease (ICD-10) codes corresponding to SDHs were identified (table 1). Hospitalized patients with a primary ICD-10 diagnosis of a SDH were recorded over a 3-year period (2017–2019) within the target population. This period was selected to mitigate year-to-year variations.
ICD-10 diagnostic codes and description for subdural hematomas (SDHs)
Subsequently, Diagnostic Related Group (DRG) codes associated with these hospitalizations were compiled. By analyzing county-level data and comparing patients’ residences to the treatment facility, it was determined that over 90% of patients with these DRG codes within the four-county primary service area received treatment at the study hospital. This indicates substantial access within the target population, crucial for accurately estimating disease rates. By employing this methodology we aimed to ensure representative data collection, facilitating a comprehensive analysis of the scope of MMAE for SDH within the specified population.
Estimation of population that may be eligible for MMAE
The medical records and imaging studies at admission were reviewed for all patients to confirm that the coded etiology—that is, traumatic versus non-traumatic—was correct and to classify the SDH as acute versus chronic or mixed. Demographic variables were recorded to divide these by age and gender. SDHs that were classified as ‘traumatic’ were further reviewed for the mechanism of trauma. These were divided into ‘fall’, ‘motor vehicle accident’ and ‘other’. The last group included patients with assault or unknown causes.
The rate of SDHs was calculated per 100 000 persons per year for the four-county primary service area with a target population of 213 000 in 2019. This was based on 90% of the patients presenting to our hospital with these diagnoses and accounting for similar rates of SDH in the remaining 10%. These rates were calculated separately for traumatic and non-traumatic SDHs. Since the focus of this analysis is to define the scope of MMAE, patients aged ≥60 with a coded ‘traumatic’ SDH were included if the cause of trauma was a fall and imaging findings indicated chronic or mixed density SDH. The results were extrapolated to the current US population estimate of 336 million based on data from the US Census Bureau (https://www.census.gov).
Results
A total of 1279 patients were hospitalized over the 3-year study period with a SDH as classified by the ICD-10 codes. Of these, there were 389 admissions from the four-county target population. After excluding repeat admissions for the same patient in the same year, 350 patients with new hospitalizations for a primary diagnosis of SDH from the target population were analyzed. The majority (76%) of patients were aged ≥60 years (figure 1). Gender distribution showed a higher proportion of men (n=197, 56%) than women (n=153, 44%). Notably, this difference was more pronounced in the younger age group, with a more even distribution observed in the ≥60 age group (figure 1). In terms of race, almost all of the patients (n=332, 95%) were classified as white/Caucasian, which is reflective of the regional demographics.
Top panel: Distribution by age groups showing that the majority of patients were aged ≥60 years. Bottom panel: Distribution of gender by age group.
The distribution of the diagnostic codes (figure 2) shows that more of these were coded as ‘traumatic’ than ‘non-traumatic’ SDHs. After a review of the medical records and imaging studies, some of the patients (n=17) that were coded as ‘non-traumatic’ were found to have a traumatic etiology and were appropriately reassigned. The most common etiology for the trauma coding was a ‘fall’, in almost 80% of the cases. While the proportion of traumatic versus non-traumatic SDHs was similar across different age groups, ‘fall’ as an etiology significantly increased with age and was the cause of over 90% of ‘traumatic’ SDHs in the ≥60 age group (figure 3). In fact, ‘fall ≥60’ represented the most common category of all SDH hospitalizations (n=156, 45%, 95% CI 39% to 50%).
Top panel: Distribution of ICD-10 codes for patients hospitalized with a subdural hematoma from the target population over a 3-year period. The bottom left panel shows that most of these patients were identified with a ‘traumatic’ code. The bottom right panel shows that a ‘fall’ was the most common etiology among patients identified as having a traumatic subdural hematoma. MVA, motor vehicle accident.
Top panel: Distribution of ‘traumatic’ versus ‘non-traumatic’ subdural hematoma by age group. The bottom panel shows that a ‘fall’ as the cause of traumatic subdural hematoma was signficantly higher in the ≥60 age group (>90%) than in those aged <60 years. MVA, motor vehicle accident.
To delineate the scope of potential MMAE candidates, patients aged ≤18 years (n=16, 4.2%) were excluded. This yielded a SDH rate of 52/100 000 persons/year (95% CI 47 to 57) for the study population, encompassing both traumatic and non-traumatic etiologies and establishing the upper limit for potential MMAE eligible patients. Excluding traumatic SDHs and confining the analysis to non-traumatic SDHs with non-acute or mixed density ‘chronic’ subdural hemorrhage resulted in a rate of 17/100 000 persons/year (95% CI 15 to 20).
Given the prevalence of falls as the predominant etiology for traumatic SDHs in patients aged >60 years, a subgroup analysis focused on this demographic was conducted. Specifically, the incidence of patients aged ≥60 years presenting with a fall and mixed density subdural hemorrhages on imaging was calculated, yielding a rate of 24/100 000 persons/year (95% CI 22 to 27) for the study population.
Finally, combining the rates of all patients with non-traumatic, non-acute SDHs aged ≥18 years along with all patients ≥60 years presenting with a fall resulted in an incidence of 41/100 000 persons/year (95% CI 36 to 47) in our study population for patients potentially eligible for MMAE. These findings were extrapolated to the current US population of 336 million (https://www.census.gov) to estimate the total number of cases (figure 4) possibly receiving MMAE at 139 387 cases per year (95 CI 121 517 to 158 168). These rates and total numbers were juxtaposed with previously published estimates16 of large vessel strokes (internal carotid artery, middle cerebral artery M1 and M2 segments and basilar artery) at 31/100 000 persons/year or 101 801 annual cases (95 CI 78 225 to 134 381) to contextualize the scope of MMAE procedures relative to endovascular stroke therapy (figure 4).
Rates of different categories of patients with subdural hematoma (SDH) and estimated total cases are shown in relation to the previously published rates of large vessel strokes from the same population.16 A potential target population for middle meningeal artery embolization procedures is defined by patients with non-traumatic, non-acute subdural hematoma aged ≥18 years combined with fall-related traumatic but non-acute subdural hematomas in patients aged ≥60 years. *Internal carotid artery, middle cerebral artery M1 and M2 segments and basilar artery.
Discussion
This analysis focused on nearly all patients with SDH from a target population treated at the study hospital, ensuring accessibility for accurate disease rate assessment. Moreover, this study population aligns with those used in previous estimations of rates for large vessel occlusion,16 18 allowing a comparison between the scope of endovascular therapy for stroke and minimally invasive procedures for SDHs. These estimations suggest a potential MMAE eligible SDH population that exceeds endovascular therapy for large vessel strokes. Our estimates are likely to be on the conservative side given the much higher reported incidence of chronic SDH in the elderly.5 7 We also only identified those patients with a primary ICD-10 code for a SDH, and there could be patients hospitalized with another primary condition and a secondary diagnosis of SDH who are not included in this analysis, further suggesting that the real estimates could be higher.
Falls among the elderly are a major public health concern leading to significant hospitalizations and mortality. Epidemiological studies19 consistently highlight falls as a leading cause of injury-related hospitalizations and mortality among older adults worldwide. Due to physiological vulnerabilities like age-related brain atrophy and weakened blood vessels, the elderly are prone to SDHs even from minor head trauma and ground level falls.20 21 Elderly patients are often on antiplatelet or anticoagulant therapy, further heightening this risk and increasing the chances of recurrence post-treatment. The cascade of inflammation and neoangiogenesis, which perpetuates chronic recurring SDHs,22 often initiates from a minor acute SDH. Elderly patients, particularly those aged ≥60 years, presenting with falls constituted almost half of all SDH hospitalizations in our analysis. Early intervention targeting the inflamed meninges may break the cycle leading to debilitating chronic SDHs in these patients.
Relative to endovascular stroke therapy—a resource-intensive endeavor necessitating round-the-clock readiness, a streamlined workflow, specialized equipment, and dedicated devices—MMAE procedures for SDHs are comparatively non-urgent, less demanding, and relatively less complex. Endovascular stroke therapy saw a steep growth in the first few years following 2015 with a doubling of the number of procedures in just 2 years and sustained a 24% compound annual growth rate for the first 6 years.16 Currently, one-third to one-half of all large and medium vessel strokes undergo endovascular therapy,16 and that is 6 years after multiple trials showing its superior efficacy. The number of MMAE procedures currently performed is unknown, but if ongoing clinical trials consistently demonstrate superior efficacy and safety of MMAE compared with standard surgical or medical management, their adoption and proliferation are likely to occur rapidly and may exceed the early growth phase of acute stroke interventions. Combined with the rate of chronic SDH, especially including falls in the elderly, it is possible that MMAE could become the dominant neurovascular procedure in the coming years. Of course, this all hinges on the current randomized clinical trials showing superior efficacy and safety of this procedure against contemporary management.
Study limitations
The findings of our study are inherently shaped by the geography, demographics, and overall health profile of the population studied. Conducted within a level 1 trauma and comprehensive stroke center serving as the primary facility for SDH cases within its catchment area, our analysis reflects a rural region situated within the ‘stroke belt’. Consequently, our study may not offer a comprehensive representation of other geographic or demographic contexts, especially those with superior geriatric health outcomes. Therefore, caution should be exercised when generalizing these results to diverse populations across different regions. To address some of these limitations, we adhered to established methodologies for population studies and provide data extraction methods that may facilitate replication in other settings.
Additionally, we identified potential inaccuracies in the coding of ‘traumatic’ versus ‘non-traumatic’ cases. For instance, patients initially presenting with traumatic SDHs may later develop chronic SDH but continue to be coded as traumatic cases. While we attempted to mitigate these coding inaccuracies by reviewing clinical notes and imaging studies for all patients, it is conceivable that coding errors may have led to missed cases.
Conclusion
MMAE for SDHs addresses one of the most prevalent and debilitating conditions among the rapidly expanding elderly population. Our projections suggest that the demographic eligible for MMAE of around 140 000 cases per year could surpass even that of large vessel strokes. This is despite these estimates erring on the conservative side, considering the higher reported incidence of chronic SDH in the elderly as well as our focus solely on patients hospitalized with a primary diagnosis of SDH. The non-emergent nature of MMAE procedures, coupled with their lower resource intensity and relative lack of complexity compared with other neurovascular interventions, could lead to a swift increase in their frequency, potentially rendering them the most performed neurovascular procedure.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
Ethics statements
Patient consent for publication
References
Footnotes
X @Ansaar_Rai, @dhairyalakhani
Contributors ATR contributed to the study design, data analysis and manuscript preparation. AAH, DAL and ART contributed to data collection. AHS contributed to manuscript review.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests ATR has a consulting agreement with Cerenovus. AHS has a consulting agreement with Cerenovus, Stryker, and Medtronic.
Provenance and peer review Not commissioned; internally peer reviewed.