Clinical manifestations

Presentation and course

Traumatic intracranial aneurysms are reported most frequently in the immediate setting of major head trauma, although multiple cases have been reported following relatively minor head injuries (29). Onset of clinical presentation of traumatic intracranial aneurysms can range from several hours to as long as 14 years after the injury, with a mean time of 2 to 3 weeks to presentation (13).

The most common presentation of traumatic intracranial aneurysms is hemorrhage, which is associated with a change in neurologic condition. The risk of subarachnoid hemorrhage is significant, with morbidity and mortality as high as 70%, but reduced to 30% with treatment. Clinical features of traumatic aneurysms include cranial nerve palsies, severe epistaxis, stupor, or coma, the latter most commonly as a result of delayed intracranial hemorrhage (14). Following trauma, the presence of these signs should raise suspicion of intracranial aneurysm. Different locations of traumatic intracranial aneurysms manifest in different clinical presentations. Infraclinoid aneurysms can present with massive epistaxis, cranial nerve palsies, headaches, or diabetes insipidus. Mao and colleagues reviewed 2335 patients with cerebral aneurysms; 15 of these patients had traumatic intracranial aneurysms due to blunt trauma (33). Epistaxis and ophthalmic pathologies were the most common presenting symptoms, each accounting for 40% of symptoms. Most of the infraclinoid aneurysms presented with recurrent or massive epistaxis.

Supraclinoid traumatic intracranial aneurysms most commonly present with progressive cranial nerve palsies, including blindness and ptosis. Headache and coma due to subarachnoid or intraparenchymal hemorrhage can be seen in supraclinoid, vertebrobasilar, or parafalcine traumatic intracranial aneurysms. Distal cortical intracranial aneurysms can present with seizures or expanding skull fracture (33). When an intracavernous aneurysm ruptures into the cavernous sinus a carotid-cavernous fistula can result. Occasionally, in infants, a skull fracture may "grow" concomitant with the enlargement of an aneurysm because the skull sutures are not fused (16). Posterior circulation traumatic intracranial aneurysms are rare and can present with oculomotor nerve palsy. Traumatic aneurysms cannot be differentiated from saccular aneurysms by these presenting clinical features, although angiographic features may sometimes distinguish them.

The location of the aneurysm depends on the nature and path of the injury. Nonpenetrating or blunt trauma results in damage to the petrous, cavernous, or supraclinoid internal carotid artery, or to the peripheral cortical branches. Distal cortical branches underlying displaced skull fractures and distal anterior cerebral artery branches such as the pericallosal, which lies against the fixed falx cerebri, are at particular risk (14). Penetrating trauma destroys structures in the direct path of the injury. Transseptal and transcallosal trajectories put middle cerebral artery branches at risk for direct injury.

In a typical patient presenting with traumatic intracranial aneurysm, the level of consciousness is initially depressed due to the trauma itself followed by a lucent period after which secondary deterioration occurs because of intracranial hemorrhage (41). The hemorrhage may be subarachnoid, intracerebral, intraventricular, or subdural, depending on aneurysm location. Headache is prominent. Compressive cranial nerve palsies caused by the enlarging aneurysm may occur later, but an abducens palsy can be present within the first few days due to raised intracranial pressure. Epistaxis, which can be massive, develops when a petrous or intracavernous internal carotid artery aneurysm associated with a basal skull fracture ruptures. The aneurysm may be asymptomatic and discovered incidentally in 10% to 20% of cases during neuroimaging. In a patient with an extraventricular CSF drain, acute sanguinous ventriculostomy output may be the sign of underlying aneurysmal rupture (14).

During war, penetrating shell fragment injuries and gunshot wounds are frequent. Most victims die immediately from the direct effects of the injury, but should they survive, the next catastrophic event is often a ventricular or brain track hematoma. Experience from the Iraq war has produced the largest study of traumatic intracranial aneurysms yet reported (06). A total of 408 patients with closed or penetrating head injuries were evaluated, 187 of them with cerebral angiography. Forty seven of these patients experienced vascular injuries, with penetrating injuries from explosive blasts constituting the majority of the cases. Traumatic intracranial aneurysms were detected in 31 cases. Other vascular injuries observed were extracalvarial aneurysms, arterial dissections, and arteriovenous fistulae. Most (16) of the intracranial aneurysms were found in the anterior communicating artery and were due to penetrating fragments through the orbitofrontal region. The rest of the intracranial aneurysms were located in the middle cerebral, internal carotid, middle meningeal, and posterior inferior cerebellar arteries. The six vertebral artery lesions (four extracalvarial aneurysms, one dissection, and one fistula) were all due to penetrating injury to the neck (06).

Prognosis and complications

The prognosis of a patient with a traumatic aneurysm depends on the severity of the inciting injury, intactness of the aneurysm, treatment rendered, and the timing of treatment. Clinical factors that correlate with outcome include: (1) vital signs on admission; (2) Glasgow Coma Scale on admission; (3) bilaterality of hemispheric injury; (4) presence of intraventricular, subarachnoid, or intracerebral hemorrhage; (5) presence of missile or intracranial bony fragments; and (6) mass effect. Surprisingly, in one prospective study of penetrating craniocerebral injury, no correlation between the presence of intracerebral hemorrhage and outcome was evident, whereas a high correlation was evident after subarachnoid hemorrhage, carrying a mortality rate of 68% (30).

The risk of subarachnoid hemorrhage is significant, with morbidity and mortality as high as 70%, but reduced to 30% with treatment. Current literature strongly supports active surgical or endovascular management of traumatic aneurysms compared to conservative therapy. Traumatic conservative management is associated with high morbidity and mortality and not recommended as traumatic aneurysms tend to enlarge over days or weeks. Rupture occurs in half the cases with an estimated mortality of 31% to 70%, whereas the mortality of surgically treated persons prior to aneurysm rupture is less than 20%, depending largely on comorbid factors (25; 02). Spontaneous healing occurs in approximately 20% of cases, usually within a few months (03; 39; 27). Pseudoaneurysms tend to grow faster than true aneurysms and appear to rebleed more frequently (28). Ultimately, the majority of traumatic intracranial aneurysms need to be aggressively managed.

Hydrocephalus, vasospasm, and cerebral edema are frequent complications.

Clinical vignette

A healthy, 6-year-old female was a restrained rear-seat passenger in an motor vehicle accident. The side impact imparted a significant rotational component to the injury. The patient was intubated in the field due to a Glasgow Coma Scale score of 4. Her initial head CT demonstrated large left frontal hemorrhage with interhemispheric extension.

Her hospital coursed involved CSF diversion by ventriculostomy and intense hyperosmolar therapy, with brief use of barbiturates to maintain intracranial pressure less than 20. Two weeks after the injury, routine head CT demonstrated new intraventricular density suggesting acute blood.

Consequently, angiography revealed a pericallosal artery aneurysm at the epicenter of the hematoma.

Typical traumatic aneurysm appearance of a broad base with irregular lumen convinced the surgeons to trap the aneurysm by craniotomy via a frontal interhemispheric approach. After opening the aneurysm and using suction to evacuate the intra-aneurysmal clot, a clip successfully isolated the aneurysm from the ACA circulation.

The patient recovered well and within two weeks was transferred to acute rehabilitation with right leg spastic paresis.

Biological basis

Etiology and pathogenesis

Traumatic intracranial aneurysms are located in regions where subarachnoid arteries transitions in an area of rigid structure. Common locations are the skull base, distal dural ring, and pericallosal and callosomarginal areas close to the falx cerebri. The shearing forces associated with the skull base result in arterial injury at the transition point of the internal carotid artery, which is fixed at the skull base in the subarachnoid space. Skull base traumatic aneurysms most commonly involve the petrous or cavernous carotid artery and are almost invariably associated with base of skull fracture. The peripheral traumatic intracranial aneurysms are divided into perifalx and distal cortical aneurysms. The distal anterior cerebral artery segments and branches can be damaged by the shearing forces against the falx cerebri. Perifalx aneurysms involve the anterior cerebral, posterior cerebral, or superior cerebellar arteries by compressing the arteries against the falx cerebri and tentorium cerebelli. Distal cortical traumatic aneurysms are due to depressed or linear skull fractures, or dural lacerations, injuring the surface cortical branches of the middle cerebral or anterior cerebral arteries (33). Traumatic intracranial aneurysms of the middle meningeal artery usually result from skull fracture crossing the artery in the temporal region (24).

Histologically, traumatic intracranial aneurysms are categorized as true aneurysms or false pseudoaneurysms or dissecting aneurysms. Compared to saccular aneurysms that have an intact adventitia and intima, true traumatic aneurysms are dilations of the arterial wall with only an intact adventitia. False traumatic pseudoaneurysms is a rupture of all layers of the intracranial vessel with an associated perivascular hematoma. Dissecting traumatic intracranial aneurysms form after trauma that splits the arterial wall layers with false lumen forming between the intima and elastica as blood enters through the intimal tears. Regardless of the histologic subtype of injury, the management remains the same, and all traumatic intracranial aneurysms need to be aggressively treated.

Epidemiology

Traumatic intracranial aneurysms constitute less than 1% of adult aneurysms; however, they account for more than 20% of pediatric aneurysms (22; 33). Unlike in adults where female and male preponderance is the same, in pediatric population, it is more commonly males that are affected, and this is thought to be due to their higher risk of blunt head injury (29). The incidence of traumatic intracranial aneurysms caused by penetrating trauma across studies is approximately 2% to 6% across studies (03). After a gunshot wound to the brain, the incidence of traumatic aneurysm in persons surviving 48 hours is 3% (30). Of 2187 persons with penetrating head injury in the Vietnam war, only two traumatic aneurysms were documented, but this number was probably an underestimate because not all brain-injured persons underwent angiography (17). When persons were evaluated systematically, as in the Iran-Iraq conflict, 3% of those with penetrating head wounds demonstrated an intracranial aneurysm (01). Among wartime patients with closed and penetrating head injuries deemed to warrant angiography, there was a 34% prevalence of vascular injuries, with traumatic intracranial aneurysms constituting the majority (06). Shrapnel and gunshot wounds show similar rates of aneurysm formation (01; 30). Stab wounds to the head, on the other hand, carry a much higher risk of all types of vascular injuries (30%), with aneurysm formation in 10% to 12% of cases (26; 15). Although closed head injury is the most common cause of traumatic aneurysms, the frequency with which they occur remains uncertain. The 10-year incidence of traumatic intracranial aneurysm after blunt traumatic brain injury was found to be 0.65% (48). In a single center experience, motor vehicle accidents were the most common cause of traumatic aneurysm after blunt head trauma (33). Males, younger age group, base of skull fracture, intracerebral hemorrhage, and high impact traumatic brain injury are risk factors for development of traumatic intracranial aneurysms (48).

The reported incidence of vascular injury in civilian penetrating brain injury (cvPBI) ranges between 38% and 50%. This risk is higher when a projectile penetrates the cranium in the fronto-basal region, when trajectory of the projectile traverses both hemispheres or is in close proximity to the circle of Willis, and when intraventricular or subarachnoid hemorrhage is present (08). Of all vascular injuries associated with civilian penetrating brain injury, traumatic intracranial aneurysms are the most common (39%), followed by arterial dissections (29%), arterial occlusion (21%), and arterio-venous fistulas (11%). Approximately 96% of the injuries are limited to the anterior circulation, namely the middle cerebral artery and internal carotid artery. Although CTA has limited overall sensitivity in detecting arterial injuries in civilian penetrating brain injury (72.7% sensitivity and 93.5% specificity), it is fairly reliable in identifying traumatic aneurysms in this patient population (100% sensitivity and specificity). Conventional angiography remains superior to CTA for detecting overall arterial injury; however, the clinical utility in the acute setting remains ambiguous (31).

A large series of civilian penetrating brain injury was reported from the level 1 trauma center at the University of Chicago. In this dataset, the frequency of vascular injury, including both the arterial and venous sinus systems, was found to be 57% higher than other civilian penetrating brain injury series (32). In part, this may be due to more inclusive definition of vascular injuries that is not restricted to only traumatic intracranial aneurysms. Analogous to the previously reported literature, arterial injury was observed in 26 out of 72 (36%) of the cohort. A total of 37 arterial injuries were described (some patients have more than one injury), the most prevalent of which was traumatic intracranial aneurysm (30%) and equal involvement of all major vessels in the anterior circulation (72% of all injured vessels), with an equal split amongst anterior cerebral artery, middle cerebral artery, and internal carotid artery.

Prevention

Traumatic intracranial aneurysms can also be seen in iatrogenic injury following endoscopic pituitary surgery, paranasal sinus surgery, skull base surgery, and ventriculostomies.

Differential diagnosis

It is important to distinguish traumatic intracranial aneurysms and true saccular aneurysms as the natural history is different between the two. A combination of history and anatomic location of the aneurysm can help differentiate the two. Angiographically, true saccular aneurysms occur at vessel branch points, whereas traumatic aneurysms occur at peripheral location near the falx cerebri or at the skull base and at non-branch points of vessels. The chance of traumatic intracranial aneurysm is much higher in the following situations: (1) a blurry or no aneurysm neck; (2) abrupt change in diameter and/or irregular wall in the parent artery; (3) aneurysm sac with delayed filling and emptying; and (4) irregular or strange aneurysm shape (37). When the history of trauma is recent and a fracture or missile track is evident, it should raise the suspicion of a traumatic etiology. The diagnosis of traumatic intracranial aneurysm should also be considered when there is: (1) delayed neurologic deterioration after trauma; (2) unusual location of hemorrhage; (3) orbitofaciocranial injury; (4) recurrent epistaxis; (5) enlarging skull fracture; or (6) progressive cranial nerve palsies.

Diagnostic workup

Penetrating head injuries produce a substantial risk of intracranial vascular injury; therefore, there should be a high clinical suspicion for traumatic intracranial aneurysms. In head trauma patients, a head CT scan is performed to document the extent of the trauma as well as the presence of intracranial hemorrhage. Cerebral edema, missile tracts, bone and other fragments, and contiguous lesions may be seen. High-resolution contrast-enhanced CT scans combined with 4-vessel cerebral angiography provided adequate data for diagnosis of vascular injuries in most cases (04). CT angiography is the screening modality of choice for the initial workup as it can be obtained rapidly. CTA can be limited by the field of view and can be further limited by superimposed brain injury, bony fragments, and metal artifact. One study, though limited by small sample size, reported that CT angiography had a 100% sensitivity and specificity in detecting traumatic intracranial aneurysms (09). With its ready availability and swift acquisition, CT angiography of the head and neck is the appropriate first-line investigation for neurovascular injury in most trauma patients, with conventional cerebral angiography employed for inconclusive CT angiography or in the setting of immediate operative intervention (47).

Although CT angiography is a sensitive noninvasive screening method for intracranial aneurysms, conventional cerebral angiography remains the reference standard for diagnosing cerebral aneurysm and is advocated as the initial screening modality by some authors (12; 14; 05).

If following blunt craniofacial injury, a patient presents with delayed neurologic deficits, intracranial bleeding in unusual subarachnoid hemorrhage, recurrent epistaxis, or if the carotid canal is involved with a basilar cranial fracture or skull base fractures, a conventional angiogram is recommended due to improved sensitivity for detection of intracranial vessel injuries (34). Additionally, in cases when bone artifact interferes with CTA imaging, DSA is recommended to allow for adequate visualization of the intracranial circulation. In military trauma patients, screening angiography has been recommended with a penetrating head injury of any kind, a known surgically treated traumatic intracranial aneurysm, a nonpenetrating blast injury to the head with a presenting Glasgow Coma Scale score of less than 8, evidence of vasospasm, or evidence of spontaneous decrease in cerebral blood flow (06). Radiographic risk factors for arterial injuries include the trajectory of the injury being proximal to the circle of Willis or being bihemispheric, the presence of subarachnoid hemorrhage or intraventricular hemorrhage, and a high severity score of the intraventricular hemorrhage or subarachnoid hemorrhage. Presence of these factors may help determine the need for a conventional angiogram (08).

The development of substantial and otherwise unexplained subarachnoid hemorrhage or delayed hematoma should also prompt consideration of vascular injury and angiography. The timing of angiography is still controversial. Late presenting aneurysms may be missed by early angiography, prompting some authorities to suggest delaying the procedure from initial presentation. Early angiography should be considered in the setting of severe head injuries, and a follow-up angiogram should be obtained if the initial study was negative (14). Bell and colleagues recommend a diagnostic angiography in war victims to be done as soon as possible; in their series, two aneurysms ruptured less than 10 days after the trauma (06). CT angiography has also been useful for preoperative surgical planning, allowing delineation of the aneurysmal shape and its anatomical relationship to surrounding vessels and bone (04; 45). When a carotid-cavernous fistula is documented, angiography with subtracted films must be carefully scrutinized because early filling of the fistula may mask an aneurysm.

A poorly defined aneurysmal neck, an irregular appearance, a location at the periphery of the vessel rather than at its bifurcation, and delayed filling and emptying of the aneurysm are angiographic features that may help differentiate traumatic from congenital or other acquired intracranial aneurysms (14).

Vasospasm may occur after either closed or penetrating head injury, but its frequency is uncertain and ranges widely in series of closed head injury (30). In wartime penetrating injuries causing traumatic aneurysms, the incidence of vasospasm can exceed 50% (06). When multiple aneurysms are present, the location of vasospasm is unreliable in determining which aneurysm has bled (20). Transcranial Doppler studies show increased velocities, suggesting vasospasm in about 40% of persons after closed head injury, which closely correlates with the amount of blood in the basal cisterns. Incidence of vasospasm peaks at 14 days and can be effectively treated with balloon angioplasty or intra-arterial nicardipine. Those with vasospasm have lower Glasgow coma scores compared to those without.

Management

The aim of management is to prevent aneurysmal rupture and bleeding and to exclude the aneurysm from the circulation, irrespective of size, once the patient is stabilized. Although a few reports in the literature show that traumatic intracranial aneurysms can resolve with time (36; 42), many reports show a high rate of expansion and rupture, and a high morbidity and mortality with rupture (02). In addition, traumatic intracranial aneurysms have an unpredictable behavior, which makes observation risky (18). Thus, most sources strongly recommend treatment of traumatic intracranial aneurysms.

There are reports of both microsurgery and endovascular treatments for traumatic intracranial aneurysms. The surgical method of treatment depends on the location and morphology of the aneurysm as well as on the nature of the inciting injury. When associated with intracerebral hemorrhage resulting in mass effect and elevated intracranial pressure, emergent open surgical treatment with evacuation of the space occupying lesion is recommended. At the same time, the aneurysm can be repaired with the preferred treatment for the aneurysm, which is to clip it while maintaining the integrity of the parent vessel. However, this is possible in only 10% to 15% of cases because of a lack of a discrete neck (01; 02). When the aneurysm is unclippable, trapping with excision, wrapping, or simple excision can be performed. This is often complicated when parent vessel preservation is important, particularly when eloquent territory is at risk. A backup strategy of aneurysm resection with bypass and trapping of the aneurysm can be considered. Because the wall of the majority of these aneurysms is made of clot, intraoperative rupture is common. The mortality rate with open surgery can be as high as 20% (23). Mortality is substantially lower when the aneurysm is unruptured. Intraoperative cerebral protection, such as barbiturate use combined with moderate hypothermia, is an essential consideration for patients in whom vessel reconstruction will require temporary occlusion of the parent vessel.

When parent vessel occlusion is an option, endovascular techniques can be considered, especially when no mass effect is present. When the traumatic aneurysm is located distally along the parent vessel, occlusion can be performed with coils or nBCA. However, when the aneurysm is located more proximally along the parent vessel, parent vessel occlusion can be performed following a balloon test occlusion. Coiling alone without parent vessel sacrifice of the aneurysm is associated with a high risk of recurrence and hemorrhage since pseudoaneurysm formation is common. Stent-assisted coiling or flow diversion have become increasingly described in the durable treatment of these lesions (38; 05; 40). If the patient fails a balloon test occlusion, one can consider clip reconstruction using a clip-wrap approach or clip occlusion with bypass.

The rate of preservation of the parent artery is higher with endovascular as compared to open brain surgery. In a study, 62% of 13 consecutive peripheral distal anterior cerebral artery (ACA) and middle cerebral artery (MCA) traumatic aneurysms were successfully embolized without compromising the parent vessel (12). Aneurysms treated endovascularly frequently require retreatment. The need for postoperative antiplatelet therapy can make endovascular treatment even more challenging, especially when a patient is presenting with trauma; however, risk of in-stent thrombosis often outweighs the risk of hemorrhage (18). Future designs may incorporate coated devices to lessen the dependence on antiplatelet agents after endovascular therapy (40).

Ligation of the proximal parent artery is the least preferred treatment and must be gradually accomplished over 48 hours to diminish the likelihood of aneurysm rupture. Aneurysms of the supraclinoid internal carotid artery should be clipped, failing which, they should be wrapped. Cavernous and petrous carotid aneurysms may be trapped surgically or endovascularly, wrapped, or excised. Peripheral branch lesions should be excised if clipping is not possible. The adequacy of collateral supply and tolerance to potential occlusion of the vessel should be assessed preoperatively whenever feasible. This may be done endovascularly in good grade patients with balloon occlusion while monitoring cerebral blood flow and neurologic status. Prophylactic intracranial revascularization prior to ligation of an aneurysm at the skull base is recommended.

Unlike the situation with spontaneous aneurysms, for traumatic intracranial aneurysms no recommendations exist regarding intervening at a certain aneurysm size. Although in the largest available series traumatic intracranial aneurysms that ruptured tended to be larger than unruptured aneurysms at diagnosis (8.275 mm vs. 3.15 mm), this was not statistically significant, and all of the aneurysms increased in size on follow-up angiography. Of 13 aneurysms that were not treated, primarily because of small size, most resolved or stabilized on follow-up angiograms, with 1 of 13 rupturing, resulting in death (06).

Outcomes

Traumatic intracranial aneurysms have a higher rate of rupture and growth compared to true saccular aneurysms. It is estimated that 40% will hemorrhage and 21% will grow in size on follow-up imaging. Most will rupture in 2 to 3 weeks after initial diagnosis.

Because traumatic intracranial aneurysms are rare, no large case studies documenting long-term outcomes are available. Moon and colleagues described their case series of patients with traumatic pseudoaneurysms located in the cavernous/ophthalmic segments and M2 segment of the middle cerebral artery (35). Treatment included trapping of the internal carotid artery, balloon occlusion of the internal carotid artery after passing a balloon occlusion test, and clipping of the middle cerebral artery lesions.

Special considerations

Pregnancy

Aneurysmal subarachnoid hemorrhage during pregnancy is a rare but serious obstetric complication. Literature on management is scant. In general, neurosurgical considerations take precedence over obstetric considerations. Ruptured aneurysms should be treated as they would in patients who are not pregnant, and unruptured aneurysms should be treated if they are symptomatic or enlarging (44).

Anesthesia

Care should be taken to prevent raising intracranial pressure during surgery. Intracranial pressure should be monitored and appropriately lowered with osmotic therapies or with periodic hyperventilation. Barbiturates, etomidate, or isoflurane are preferred anesthetic agents because they decrease cerebral metabolic rate and provide some protection to the ischemic penumbra. Complete circulatory arrest with deep hypothermia is necessary in complex cases but has not been specifically evaluated in traumatic aneurysms.