Blunt force trauma is an impact injury to the body that does not break the skin but can cause significant damage beneath the surface. An aneurysm is a balloon-like bulge that forms in the wall of a blood vessel due to a localized weakness. When a blood vessel wall is subjected to extreme force, such as from a car accident or severe fall, it can be damaged, leading to the formation of an aneurysm, particularly a pseudoaneurysm. This serious complication of non-penetrating trauma most often affects the arteries in the head, neck, and chest. The mechanical forces from the injury directly compromise the integrity of the vessel structure, which can then balloon outward under the continuous pressure of circulating blood.
The Mechanism of Arterial Wall Damage
The wall of a healthy artery is composed of three distinct layers: the inner lining called the intima, the middle muscular layer known as the media, and the outer connective tissue layer called the adventitia. Blunt force trauma creates powerful compressive, stretching, and shearing forces that can physically tear or damage these layers. The injury often begins with a tear in the delicate intima, exposing underlying layers to circulating blood.
This initial tear allows blood to forcefully enter the middle layer, separating the layers in a process called arterial dissection. This dissection creates a false channel for blood flow within the artery wall itself, weakening the overall structure.
If the injury progresses and ruptures all three layers, the blood may be contained only by surrounding tissue, forming a clot-lined sac. This sac, contained only by outer tissue and not the original vessel wall layers, is specifically called a pseudoaneurysm, or “false aneurysm.” This is the most common form of aneurysm following blunt force trauma. Because the pseudoaneurysm wall lacks the strong arterial layers, it is inherently unstable and carries a higher risk of rupture and rapid growth compared to other aneurysms.
Types and Locations of Traumatic Aneurysms
Trauma-induced aneurysms are broadly categorized based on their anatomical location, typically occurring where arteries are fixed or run close to bony structures.
Intracranial aneurysms, found within the brain, often result from severe head trauma, such as skull fractures or rapid deceleration injuries. These cerebral pseudoaneurysms commonly affect distal arteries, such as the anterior or middle cerebral arteries, where the vessel is sheared against fixed structures like the falx cerebri or the skull base.
Extracranial aneurysms, outside the skull, frequently involve the carotid and vertebral arteries in the neck. These injuries occur when the neck is subjected to extreme hyperextension, severe rotation, or direct compression, as seen in certain sports injuries or motor vehicle accidents. The sudden, violent movement can stretch and tear the arterial walls against the vertebrae.
Traumatic aneurysms are predominantly pseudoaneurysms, meaning they are contained hematomas outside the true vessel wall, which distinguishes them from the more common saccular aneurysms that form due to degenerative causes.
Symptoms and Diagnostic Imaging
The symptoms of a traumatic aneurysm can be highly varied and often do not appear immediately following the injury, sometimes manifesting days or even weeks later, which complicates diagnosis.
For extracranial aneurysms in the neck arteries, symptoms may include localized neck pain, a headache that progressively worsens, or neurological deficits like stroke-like weakness or numbness. Carotid artery involvement can also cause Horner’s syndrome, which is a combination of a drooping eyelid and a constricted pupil on the affected side.
Intracranial aneurysms often present with a severe, sudden headache, which may indicate rupture and bleeding into the brain tissue or surrounding spaces. Other symptoms include vision changes, such as double vision or loss of sight, or cranial nerve palsies caused by the enlarging aneurysm pressing on nearby nerves. Any delayed neurological decline after blunt trauma should raise suspicion due to the high risk of hemorrhage.
Diagnosis relies on specialized imaging techniques to visualize the damaged blood vessels and the aneurysm sac. Computed Tomography Angiography (CTA) is often the initial, quick test, using an injected dye to create detailed images of the blood vessels. Magnetic Resonance Angiography (MRA) is another non-invasive option providing high-resolution images without the use of X-rays.
The most definitive method is Digital Subtraction Angiography (DSA), or cerebral angiography. This invasive procedure involves threading a catheter through an artery up to the affected vessel while injecting a contrast agent. DSA provides the clearest, real-time images of blood flow and the aneurysm’s precise structure, which is essential for treatment planning.
Treatment Approaches
Management of traumatic aneurysms is urgent due to their unstable nature and high risk of rupture, which is significantly greater than that of non-traumatic aneurysms. The primary goal of treatment is to secure the damaged vessel and prevent life-threatening hemorrhage. The choice of intervention depends heavily on the aneurysm’s location, size, and the patient’s overall condition.
Endovascular repair is often the preferred, least invasive option, performed using a catheter inside the blood vessel. This approach includes coiling, where platinum coils are packed into the aneurysm sac to promote clotting and seal the defect. Stenting involves placing a mesh tube to divert blood flow away from the damaged area, allowing the vessel wall to heal. Specialized flow-diverting stents are used for larger or complex pseudoaneurysms, encouraging the vessel wall to seal off the sac entirely.
Surgical intervention is necessary for lesions that are not easily accessible or treatable endovascularly. Open surgery may involve clipping the aneurysm’s neck to exclude it from circulation or trapping the damaged segment. If the parent vessel must be sacrificed, a bypass procedure may be performed to restore necessary blood flow to the downstream brain tissue.
For very small, stable aneurysms, observation with close follow-up imaging may be considered alongside medical management. Antiplatelet therapy may be used to prevent clot formation, but this requires careful monitoring due to the inherent instability of post-traumatic pseudoaneurysms.