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BOSTON — In U.S. Special Operations Forces personnel, greater repeated blast exposure is associated with a higher prevalence of intracranial aneurysms, according to a recent study. An intracranial aneurysm is a weak, bulging area in a blood vessel wall in the brain, often described as balloon-like. While many remain asymptomatic until discovered or ruptured, a burst aneurysm causes a life-threatening hemorrhage that requires immediate medical emergency care.
The retrospective study published in the journal Radiology determined the prevalence of structural brain MRI abnormalities in Special Operations Forces personnel and examined their association with cumulative blast exposure. This was quantified using the generalized blast exposure value.1
U.S. Special Operations Forces, which include the Green Berets, 75th Ranger Regiment, Navy SEALs and the Marine Forces Special Operations Command, among others, are elite, highly trained military units designed for covert, high-risk and time-sensitive missions beyond the capability of conventional forces. They also are a uniquely high-risk population for brain injury because of frequent exposure to both low- and high-level blasts during combat operations and tactical training. Unlike single-event traumatic brain injuries, these exposures are often repetitive, subclinical and cumulative, which raises concerns about potential long-term neurologic effects that conventional diagnostic criteria might not capture.
MRI is typically used to evaluate traumatic brain injuries, but interpreting structural brain abnormalities in military populations is challenging because of high prevalence of nonspecific lesions observed in both patients with traumatic brain injuries and noninjured controls. That can complicate efforts to distinguish injury-specific markers from incidental findings.
Structural abnormalities, including vascular lesions, are most prevalent in Special Operations Forces, and the study investigated whether any of these findings correlate with cumulative blast exposure as quantified by generalized blast exposure value. This information could improve clinical interpretation of routine MRI in blast-exposed military personnel and inform future screening strategies, the study authors suggested.
The study authors are affiliated with Massachusetts General Hospital in Boston; University of Genoa in Genoa, Italy; University of Regensburg Medical Center in Regensburg, Germany; Home Base Program, Massachusetts General Hospital in Charlestown, MA; and Home Base Program & Harvard Medical School in Boston.
“This study is the first to examine the relationship between cumulative blast exposure and structural brain MRI findings in a large group of U.S. Special Operations Forces,” said lead author Sara De Giorgi, MD, radiologist and postdoctoral research fellow in neuroradiology at Massachusetts General Hospital, in a press release by the Radiological Society of North America. “We found that intracranial aneurysms were more common in individuals with higher blast exposure.”
Click to Enlarge: Association between cumulative blast exposure and aneurysm presence. (A) Bar graph shows the aneurysm prevalence among participants with high versus low cumulative blast exposure, based on the sample median of log10(generalized blast exposure value [GBEV] + 1) = 6.55. Aneurysms were more frequent in the high-exposure group (9.5%; 21 of 220 participants) compared with the low-exposure group (2.7%; six of 220 participants). (B) Forest plot shows the odds ratio and relative risk for aneurysm presence in the high-exposure group compared with the low-exposure group. Estimates are presented with 95% CIs (horizontal bars). The vertical dashed line at x = 1 indicates the null effect. Source: Radiological Society of North America
In the study, 564 Special Operations Forces personnel (mean age 43 years old, 563 total men) were evaluated in the Comprehensive Brain Health and Trauma Program. All participants underwent 3T brain MRI with time-of-flight MR angiography (MRA). Imaging findings were extracted from structured neuroradiology reports. Blast exposure was quantified using the generalized blast exposure value, a numerical score that measures the cumulative impact of repeated low-intensity blasts (e.g., from training). Using a quantitative measure of blast exposure enabled the researchers to identify the association of structural brain MRI abnormalities with cumulative blast exposure in a population where MRI findings are often nonspecific and challenging to interpret, the press release explained.
The study’s most prevalent MRI finding was white matter hyperintensities (215 of 564 participants, 38.1%), followed by intracranial aneurysms (33 of 564 participants, 5.9%). Among all MRI findings, only intracranial aneurysms were associated with cumulative blast exposure. No association was observed for other structural abnormalities, including white matter hyperintensities, the investigators pointed out.
The researchers found that aneurysm prevalence was greater in the high-exposure group (21 of 220 participants, 9.5%) compared to the low-exposure group (6 of 220 participants, 2.7%), the press release reported.
“Intracranial aneurysms were three times more common in highly exposed personnel,” De Giorgi said in the press release. “Even after accounting for other health factors such as age and blood pressure, the association remained significant. These findings suggest that repeated blast exposure may leave a measurable vascular signature in the brain.”
Special Operations Forces personnel have a vastly different injury pattern compared to civilian trauma. These servicemembers can face years of low-level blast exposure from shockwaves that pass through the brain with no external injury visible, which can leave lasting effects that are only now being detected with advanced imaging, De Giorgi explained.
The study’s results suggested a possible long-term vascular effect of repeated low-level blast exposure during years of service, which can be observed with routine MRI scans. The authors recommended that screening MRAs may be warranted in this population of servicemembers.
In an editorial on subclinical repetitive head trauma, the editorial authors discussed the findings of this Radiology study on repeated blast exposure. They noted the study found that almost 40% of aneurysms originated from the cavernous segment of the internal carotid artery, which is unexpected, yet mechanistically plausible. The involvement of the cavernous internal carotid artery was theorized to be due to repetitive blast exposure contributing to focal vascular remodeling in segments under high strain.2
Typically, traumatic intracranial aneurysms are the result of a single impact injury, but this study’s findings suggest that repetitive subclinical blast exposure may result in chronic cerebrovascular injury different from those observed in conventional trauma registries. The study provides a valuable addition to efforts to create normative data benchmarks for military personnel, according to the editorial writers.
Limitations of the study included lack of longitudinal follow-up of these aneurysms, which were mostly small, and the unexplored clinical implications of their extradural location. However, the editorial writers acknowledged this study adds immense value to understanding the changes in the cerebrovascular compliance in response to chronic repetitive blast exposure.
While the study adjusted for age, body mass index, systolic and diastolic blood pressure and total cholesterol, future analyses should include additional parameters such as modifiable lifestyle factors for aneurysm development (e.g., smoking, coffee consumption, sleep and physical activity), the editorial writers recommended.
- De Giorgi S, Diociasi A, Khalid RN, Strotzer QD, Degn P, Rand KE, Gabali S, Hirschberg RE, Sorg SF, Lev MH, Gupta R. Brain MRI Analysis of Cumulative Blast Exposure and Intracranial Aneurysms in Special Operations Forces. Radiology. 2026 Apr;319(1):e252415. doi: 10.1148/radiol.252415. PMID: 41979463.
- Maralani PJ, Pai V. Subclinical Repetitive Head Trauma: A Potential New Risk Factor for Brain Aneurysms. Radiology. 2026 Apr;319(1):e260599. doi: 10.1148/radiol.260599. PMID: 41979456.