Clinical Evaluation

TICAs of the posterior circulation frequently occur in the setting of severe head trauma, and as previously stated, often involve penetrating injuries to the cranium or skull fractures adjacent to intracranial arteries. Thus, most patients present in coma or with a depressed level of consciousness. The exception to this rule is low-velocity penetrating trauma, such as stab wounds, where patients may not have alteration of consciousness or intracranial bleeding due to the severity of head trauma. The neurosurgeon must maintain a high level of suspicion in these cases, as the incidence of false aneurysm formation in high-velocity and low-velocity penetrating head trauma is 4 and 10%, respectively.

The delay between the initial trauma and hemorrhage from the false aneurysm can range from hours to months, but averages between 2 and 3 weeks. TICA should remain high on the differential diagnosis for any patient with a history of head trauma that presents with a significant amount of subarachnoid hemorrhage (SAH) on the initial noncontrast head computed tomography (CT) scan or develops a delayed sudden neurological decline.

Imaging

Widespread use of contrast-enhanced CT imaging has been proposed as a reason for a decreased incidence in diagnosing TICAs as it has replaced traditional catheter angiography in the initial evaluation of head trauma.

In the setting of severe head trauma, CT imaging of the brain will typically reveal diffuse intracranial hemorrhage (extra-axial, intracerebral, subarachnoid, or frequently a combination). A significant amount of SAH should raise the suspicion for presence of a TICA. Similarly, the location of hemorrhage will lend a clue as to the location of a possible TICA—for example, isolated fourth ventricle hemorrhage is suspicious for a traumatic aneurysm of the distal posterior inferior cerebellar artery (PICA).

Cerebral catheter angiography remains the gold standard for the identification of TICA. TICAs frequently appear as an irregular caliber change or dilation of an artery. In contrast to saccular aneurysms, TICAs most often do not occur at an arterial branching point. Care must be taken to evaluate the entirety of the posterior fossa circulation, including both PICAs beyond their origin from the vertebral artery. This is accomplished via injection of both vertebral arteries. Failure to visualize both PICAs may lead to missed diagnosis of TICA of the distal PICA ( 1 in algorithm ).

Suspicion should be maintained for pseudoaneurysm formation in the setting of penetrating trauma as well as blunt trauma with skull fractures adjacent to the posterior arterial circulation. In the setting of penetrating trauma, it is important to have a low threshold for obtaining follow-up vascular imaging particularly if there was a significant amount of associated SAH even in the setting of negative imaging at initial evaluation. Quality of noninvasive vascular imaging (CT angiography or MR angiography) varies by institution, as does the availability of digital subtraction angiography. Therefore, decisions on what type of imaging to obtain and the specific follow-up interval should be made on a patient- and institution-specific basis.

Differential Diagnosis

The presence of a posterior circulation aneurysmal dilatation in the setting of an adjacent penetrating trauma essentially confirms the diagnosis. Arteriovenous fistulas can also occur following a penetrating head injury and should be ruled out. In rare cases, aneurysmal rupture could precede a traumatic head injury and one may encounter a more typical saccular-type (true) aneurysm in the posterior circulation.

Choice of Treatment and the Influence of Intracerebral Hematoma

Careful evaluation of the mechanism of injury and the mode of presentation must be made in order to determine appropriate treatment strategies. As mentioned earlier, blunt dissecting arterial injuries, particularly those involving the vertebral arteries, may present with either ischemic sequelae if the dissection plane is subintimal or with hemorrhage if the integrity of the adventitia is compromised. The presence of an aneurysmal dilatation or vessel irregularity in close proximity to a penetrating trauma implies pseudoaneurysm formation. While conservative therapy with antiplatelet or anticoagulation may be appropriate for “ischemic” type injuries ( 3 in algorithm ), traumatic pseudoaneurysms should be treated by parent vessel sacrifice if possible (see below) ( 4 in algorithm ). Although described in several case reports, we do not believe that vessel-sparing procedures such as clipping or coil obliteration of the pseudoaneurysm dome can reliably achieve definitive treatment in these circumstances due to the injury involving all layers of the vessel wall. If exclusion of the aneurysm with preservation of the parent vessel is to be attempted, it should be performed under direct microsurgical visualization such that clip ligation of the aneurysm neck is confirmed to include healthy vessel wall layers. There are reports of endovascular treatments of TICAs which spare the parent vessel, but one must be mindful of the risk of recanalization and delayed rupture for the aforementioned reasons.

The choice of treatment of TICAs of the posterior circulation depends on the specific location of the aneurysm, the type of injury, the clinical status of the patient, and the presence of associated injuries such as intracerebral hematoma or parenchymal injury to the territory supplied by the affected artery. Endovascular therapy, including coil occlusion of the affected artery segment or the use of liquid embolics, is recommended in cases where endovascular access is feasible and noneloquence of the distal territory supplied by the affected artery is clear. On the other hand, microsurgery is reserved for cases that require aneurysm trapping with distal revascularization or in patients with an associated hematoma that requires surgical evacuation ( 5 in algorithm ). Knowledge of the various segments beyond which a posterior circulation vessel can be safely occluded with minimal clinical sequelae is crucial (see below). In the setting of significant parenchymal injury to an eloquent cerebral territory supplied by the injured vessel, stand-alone vessel sacrifice without distal bypass can be considered without additional morbidity. For example, a posterior cerebral artery (PCA) pseudoaneurysm in a patient with an associated ipsilateral occipital lobe hemorrhage and homonymous hemianopsia may still be considered for therapeutic occlusion of the affected PCA segment without the need for a bypass ( 6 in algorithm ).

In cases where parent vessel sacrifice alone would result in unacceptable ischemic sequelae, either open surgical resection and end-to-end anastomosis or trapping and bypass graft to the distal arterial segment is necessary. The preferred location for bypass and type of graft is determined by the specific vessel ( 4, 5 in algorithm ). For example, a proximal PICA injury should be treated by resection of the pseudoaneurysm and end-to-end anastomosis or trapping and distal PICA–PICA or OA–PICA anastomosis, whereas a proximal PCA pseudoaneurysm often requires an end-to-side STA-PCA bypass.

In cases where the diagnosis of pseudoaneurysm has been made and a significant hematoma requiring surgical evacuation exists, careful consideration should be given to open surgical parent vessel sacrifice at the time of clot evacuation. Alternatively, endovascular sacrifice can be performed followed by surgical evacuation of the hematoma.