Can Head Trauma Cause an Aneurysm?

Head trauma can cause an aneurysm. Traumatic intracranial aneurysms are uncommon, representing roughly 1% of all intracranial aneurysms, but they are well documented in the medical literature and carry serious consequences when they occur. The mechanism typically involves physical damage to the wall of a blood vessel inside the skull, either from blunt force, penetrating injury, or the shearing forces that the brain experiences during rapid acceleration and deceleration. What makes these lesions particularly dangerous is how easily they are missed on initial imaging, sometimes not becoming visible for days or weeks after the original injury.

How Trauma Damages Blood Vessels Inside the Skull

The arteries that supply the brain sit in tight spaces, running along bony ridges, through narrow canals, and next to rigid structures like the falx (the membrane dividing the two brain hemispheres). When the head absorbs a blow, the brain moves relative to these fixed structures. That relative movement creates shearing and rotational forces that can tear or weaken an arterial wall. A closed head injury, the kind where nothing penetrates the skull, can generate enough of these forces to damage a vessel and set the stage for an aneurysm to develop over subsequent days or weeks.¹

Penetrating injuries are more straightforward: a projectile or bone fragment physically lacerates the artery. But blunt trauma does not need to puncture anything to be dangerous. The acceleration-deceleration forces from a car crash, a fall, or an assault can stretch an artery beyond its tolerance. Once the vessel wall is weakened, blood pressure does the rest, gradually ballooning the damaged segment outward. Traumatic brain injury has been identified as a direct cause of aneurysm formation even in people who had no pre-existing vascular problems before the injury.²

Certain locations are more vulnerable than others. Arteries running along the skull base or in deep midline positions near the falx are especially prone to shear-related damage. Traumatic aneurysms of the pericallosal artery, which runs along the inner surface between the hemispheres, are a recognized subset precisely because that artery’s proximity to the falx makes it mechanically vulnerable during head impacts.³

Traumatic Aneurysms Versus Pseudoaneurysms

Not all trauma-related bulges on an artery are the same thing. A true aneurysm involves stretching of all three layers of the vessel wall. A pseudoaneurysm, or “false aneurysm,” occurs when the inner layers are torn and blood is contained only by the thin outer layer or by surrounding tissue. Pseudoaneurysms are the more common result of trauma, and they are also more dangerous because the wall holding the blood back is far weaker.

Posterior circulation pseudoaneurysms, involving the vertebral and basilar arteries at the back of the brain, are considered particularly underdiagnosed. Despite being rare, they carry a mortality rate estimated at 40 to 60%, largely because they tend to rupture before they are discovered.² The distinction between a true aneurysm and a pseudoaneurysm matters clinically because it influences how urgently treatment is needed and which techniques are appropriate, but from the patient’s perspective, both are outpouchings on an artery that can bleed catastrophically.

When Trauma Ruptures an Aneurysm That Was Already There

There is a second way head trauma and aneurysms intersect that gets less attention: a blow to the head can rupture a pre-existing aneurysm that the person never knew about. Unruptured brain aneurysms are surprisingly common in the general population, present in roughly 2 to 3% of adults. Most never cause symptoms. But a sudden spike in blood pressure from a head impact, or the direct mechanical force transmitted through the skull, can push a vulnerable aneurysm past its breaking point.

This creates a real diagnostic puzzle. When someone arrives at a hospital after head trauma and imaging reveals a subarachnoid hemorrhage from a ruptured aneurysm, it is difficult to determine whether the trauma caused the aneurysm, ruptured a pre-existing one, or whether the aneurysm actually ruptured first and caused the person to collapse and hit their head. Without a detailed pre-trauma medical history, untangling this sequence of events can be nearly impossible.⁴

That ambiguity has real consequences. A patient found unconscious at the bottom of a staircase with a ruptured aneurysm might have fallen because the aneurysm bled, or the aneurysm might have bled because of the fall. The answer can change everything about medical management and legal accountability.

Why These Aneurysms Are Easy to Miss

One of the more unsettling aspects of traumatic intracranial aneurysms is that they often do not show up on the first round of imaging. Research reviewing prior case reports has found that the rate of detecting a traumatic aneurysm on the day of injury is only about 54%. In nearly half of cases, the lesion needs time to “mature,” meaning the damaged vessel wall gradually weakens and balloons outward over days to weeks before it becomes visible on a scan.⁵

This is a problem because bleeding from traumatic aneurysms often occurs within the first two weeks after injury. A patient can be discharged from the hospital after what appears to be a routine recovery from a head injury, only to suffer a devastating hemorrhage days later. One reported case involved a patient who experienced a seizure 46 days after the original brain injury while in rehabilitation; imaging revealed a large ruptured pericallosal artery aneurysm that required emergency surgical clipping.⁶

The imaging tools themselves also have limitations. CT angiography, the workhorse scan used in most emergency departments, performs reasonably well for detecting vascular injuries in the neck but is demonstrably less reliable for intracranial injuries. One study comparing CT angiography to traditional catheter-based angiography for penetrating brain injuries found that CT angiography’s diagnostic accuracy was notably worse for injuries inside the skull than outside it.⁷ For patients with skull-base fractures near major blood vessels or any sign of vessel-wall irregularity, repeated screening is advisable rather than relying on a single negative scan.⁵

Surgical and Endovascular Treatment

Because traumatic aneurysms, especially pseudoaneurysms, carry such a high risk of rupture, the goal of treatment is to exclude the aneurysm from the circulation as quickly as possible. Waiting and watching tends to produce worse outcomes than active intervention. The available approaches generally fall into a few categories:

Surgical clipping or trapping: A neurosurgeon places a metal clip across the neck of the aneurysm or isolates the damaged segment entirely. In some cases, the damaged artery must be sacrificed, and a bypass is performed to reroute blood flow around the trapped segment. One reported case involved a ruptured pseudoaneurysm on the middle cerebral artery that was treated by trapping the damaged section while a bypass from the superficial temporal artery maintained blood flow to the downstream brain tissue.⁸
Flow-diverter stents: A mesh tube is threaded through the blood vessels and deployed across the damaged segment, redirecting blood flow away from the aneurysm while preserving the main artery. This approach has shown promising results. A review of pediatric cases treated with flow diversion alone reported a high rate of complete aneurysm obliteration with few complications.⁹ In adults, single-center experience with flow-diverter stents for traumatic internal carotid artery aneurysms has confirmed that the technique can safely eliminate the aneurysm while conserving the parent artery.¹⁰
Endovascular coiling: Platinum coils are packed into the aneurysm sac through a catheter to promote clotting and seal it off. This works better for true aneurysms with a defined neck than for pseudoaneurysms, which often lack enough intact wall to hold coils in place.

For extracranial traumatic aneurysms affecting the carotid or vertebral arteries in the neck, the picture can be somewhat less urgent. A prospective study tracking patients with traumatic cerebrovascular injury found that roughly 39% of extracranial traumatic aneurysms were no longer visible on follow-up imaging, another 39% had gotten smaller, and only about 19% had grown. No patient in that cohort suffered a stroke after antiplatelet therapy was started.¹¹ This suggests that not every trauma-related aneurysm requires immediate procedural intervention, but close monitoring remains essential.

Blast Exposure and Aneurysm Risk in Military Personnel

An emerging area of research links cumulative blast exposure to a higher prevalence of brain aneurysms even in the absence of a single dramatic head injury. A study of 564 Special Operations Forces members who underwent brain MRI found intracranial aneurysms in about 6% of the group overall. But when the researchers split the group by cumulative blast exposure, the difference was stark: roughly 9.5% of the high-exposure group had aneurysms, compared to about 2.7% of the low-exposure group. The odds of having an aneurysm were nearly four times higher for those with greater blast exposure, and this association held even after accounting for other variables.¹²

This finding is significant because blast waves produce a different kind of mechanical stress on the brain than a conventional blow to the head. The pressure wave passes through the skull and subjects blood vessels to rapid compression and expansion. The fact that cumulative exposure, not just single high-intensity events, was linked to aneurysm presence suggests that repeated low-level blasts may cause progressive vessel-wall damage. Among all brain MRI findings evaluated in the study, intracranial aneurysms were the only one statistically associated with cumulative blast exposure.¹²

Children and Traumatic Aneurysms

Traumatic aneurysms make up a disproportionately large share of all intracranial aneurysms in children. In adults, the vast majority of brain aneurysms are the “berry” type that form spontaneously at vessel branching points, typically influenced by high blood pressure, smoking, or genetic factors. In children, those risk factors have not had time to operate, so the causes of aneurysms skew differently. Reported estimates suggest traumatic aneurysms account for 14 to 39% of all pediatric intracranial aneurysms.¹³

The same review found that in children, traumatic aneurysms typically arise at the skull base or from the more distal branches of the anterior and middle cerebral arteries, consistent with direct vessel-wall injury or acceleration-induced shear.¹³ This means that for any child presenting with an intracranial aneurysm, a careful history for prior head trauma is particularly important, even if the injury seemed minor at the time.

Aneurysms from Surgical Procedures

Trauma does not have to come from an accident or assault. Surgical procedures on or near the skull base can inadvertently injure an intracranial artery and trigger aneurysm formation. These iatrogenic traumatic aneurysms are rare, but when they occur, the consequences are serious given the risk of delayed intracranial hemorrhage and the complexity of managing a vascular injury in a recently operated-on surgical field.¹⁴

One reported case involved a patient undergoing routine endoscopic sinus surgery for chronic sinusitis who suffered an accidental injury to a branch of the anterior cerebral artery, resulting in a pseudoaneurysm.¹⁴ Most surgical-related cases in the literature have followed transsphenoidal surgery, an approach through the nose to reach the pituitary gland, where the operative corridor passes close to major arteries.¹⁵ These cases are a reminder that any procedure involving instruments near intracranial vessels carries some risk of vascular injury, and post-operative monitoring should account for that possibility.

The Medicolegal Dimension

The question of whether head trauma caused or contributed to an aneurysm rupture comes up frequently in legal and forensic settings. If a person dies from a ruptured brain aneurysm after being assaulted, was the attacker responsible for the death? The answer often hinges on whether the aneurysm existed before the trauma and, if so, whether the trauma caused it to rupture.

A published forensic case report illustrates how this plays out. An autopsy determined that the cause of death was massive intracranial hemorrhage from a ruptured aneurysm of the internal carotid artery, associated with head trauma from blunt and sharp force. The forensic team concluded that the aneurysm rupture was “strictly correlated” to the head trauma, likely through a combination of acceleration-deceleration forces and the body’s biochemical stress response to injury. The medicolegal conclusion was that whoever was responsible for the head trauma should be considered accountable for the death.¹⁶

Cases like this underscore that the medical and legal communities do recognize head trauma as a legitimate cause of aneurysm rupture, even when a pre-existing aneurysm was present. The “eggshell skull” doctrine in many legal systems holds that you take your victim as you find them: if someone has an undiagnosed aneurysm and your assault causes it to burst, the pre-existing vulnerability does not reduce your liability. Forensic pathologists evaluating these cases rely on autopsy findings, the pattern and severity of head injuries, the location of the aneurysm relative to the trauma, and the timeline of events to establish causation. The integration of all available evidence, rather than any single finding, drives the conclusion.¹⁶

For patients, families, and attorneys navigating these situations, the key takeaway is that the relationship between trauma and aneurysms is medically established and legally actionable, but proving the connection in any individual case requires detailed clinical and pathological evidence. The ambiguity that makes diagnosis so challenging in the hospital also makes causation difficult to prove in a courtroom.

1
PubMed Central. Traumatic Intracranial Aneurysm Formation following Closed Head Injury
2
PubMed Central. Post-traumatic intracranial pseudo-aneurysms of posterior circulation: a comprehensive review of an under-diagnosed and rare entity
3
Neurotrauma Reports. Traumatic Pericallosal Artery Aneurysms: A Systematic Review of Clinical Presentation, Treatment, and Outcomes
4
PubMed. The relationship of blunt head trauma, subarachnoid hemorrhage, and rupture of pre-existing intracranial saccular aneurysms
5
PubMed Central. Delayed massive epistaxis from traumatic intracranial aneurysm after blunt facial injury
6
PubMed. Delayed traumatic cerebral aneurysm after brain injury
7
Journal of Neurosurgery. A comparison of digital subtraction angiography and computed tomography angiography for the diagnosis of penetrating cerebrovascular injury
8
PubMed Central. Ruptured proximal middle cerebral artery traumatic pseudoaneurysm treated with bypass-assisted trapping surgery: A case report
9
PubMed. Endoluminal flow diversion as a primary treatment strategy for pediatric traumatic intracranial aneurysms: a case-based review of literature
10
PubMed. Treatment of Traumatic Internal Carotid Artery Aneurysm by Flow-Diverter: A Single-Center Experience
11
Journal of Neurosurgery. Extracranial traumatic aneurysms due to blunt cerebrovascular injury
12
RSNA / Radiology. Brain MRI Analysis of Cumulative Blast Exposure and Intracranial Aneurysms in Special Operations Forces
13
SpringerLink / Childs Nervous System. Traumatic intracranial aneurysms in childhood and adolescence. Case reports and review of the literature.
14
PubMed. Iatrogenic traumatic intracranial aneurysm after endoscopic sinus surgery
15
PubMed. Traumatic intracranial aneurysms complicating anterior skull base surgery
16
Forensic Science International: Reports. Medico-legal analysis of the correlation between head trauma and aneurysm rupture: A case report