Introduction

Traumatic intracranial aneurysms (TICAs) can present with both diagnostic and management challenges. Intracranial aneurysms related to trauma comprise ≤1% of all cerebral aneurysms and are associated with morbidity and mortality rates as high as 50%. TICAs are most commonly associated with blunt head trauma and less commonly a result of penetrating trauma. TICAs are more commonly reported in the pediatric population rather than adults. The delayed presentation and difficult diagnosis of TICAs can contribute to the high mortality rates ( 1 , 2, 3 in algorithm ). A male predominance has been described, likely attributable to the greater frequency of head trauma in young males. Traumatic aneurysms typically involve vessels in the anterior circulation, likely explained by the arteries’ relationship to the falx cerebri and skull base, which can result in shearing forces during trauma leading to arterial wall destruction and aneurysm formation. Traumatic aneurysms tend to form distal on the anterior cerebral artery (ACA) and are at risk of being missed on diagnostic testing. This potential for delayed diagnosis can also help explain the high morbidity and mortality rates observed in these patients.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Which traumatic brain injury patients have a high risk of TICA and when should they undergo vascular neuroimaging?

   
   
2. 
   

   Open versus endovascular treatment for TICAs.

   
   
3. 
   

   Ideal timing for TICA treatment.

Whether to Treat

Most authors agree that surgical treatment of traumatic aneurysms is indicated because of their very poor natural history. The morbidity and mortality of untreated ruptured TICAs can be as high as 50 to 70%, whereas the morbidity and mortality with surgical treatment is 15 to 30%. The common occurrence of these lesions on the cavernous and paraclinoid internal carotid artery (ICA; ▶ Fig. 34.1 ) and distal ACAs allows for acceptable surgical exposure through a pterional or interhemispheric fissure. Distal aneurysms can be challenging for endovascular access.

Conservative Management

Conservative management of TICAs is associated with high morbidity and mortality, and is typically not recommended. However, one study estimated that 20% of all TICAs will spontaneously resolve and proposed that repeat angiography be performed for observation and recommended surgical intervention only in cases with aneurysm enlargement or neurological deterioration. The majority of studies, however, have consistently demonstrated that spontaneous resolution of TICAs is improbable with an estimated 40% of TICAs hemorrhaging and 21% enlarging on follow-up imaging. Ultimately, the large majority of the published literature supports early and aggressive management of traumatic aneurysms ( 7 in algorithm ).

Anatomical Considerations

Traumatic aneurysms are classically located in regions were subarachnoid arteries are in transition from or in contact with a rigid structure. The most common locations for TICAs include distal branches of ACA, pericallosal, callosomarginal, and the proximal ICA. The proximal ICA is at risk due to it being fixed at the distal dural ring and transitioning at that point into the subarachnoid space (▶ Fig. 34.1 ).

Histologically, traumatic aneurysms can be categorized as true, false (or pseudoaneurysms), dissecting, or mixed. True TICAs are a dilation of the arterial wall in which only the adventitia is intact, as opposed to saccular aneurysms that involve both the adventitia and intima. A rupture of all arterial layers with associated perivascular hematoma formation describes false TICAs, considered the most common histological subtype. Dissecting TICAs form following a traumatic event splitting the arterial wall layers with false lumen forming between the intima and elastica as blood enters through intimal tears. Mixed TICAs form following the posttraumatic rupture of true aneurysms with false lumen development and hematoma formation. The histological type is not clinically relevant as the high risk of hemorrhage warrants intervention regardless, and angiography cannot always reliably differentiate between subtypes.

Classification/Pathophysiology

In 1988, Buckingham et al reported that TICAs secondary to blunt injury can be classified as skull base or peripheral. Skull base TICAs are classically associated with shearing forces resulting in arterial injury at transition points from being fixed in the skull base to being free in the subarachnoid space (▶ Fig. 34.1 ). Shearing forces can also damage distal ACAs when they impact the falx cerebri. More distal, cortical arteries can suffer TICAs when local trauma results in linear skull fractures that can traumatize underlying arteries. Location of the aneurysm is strongly indicative to the mechanism of injury. The anterior circulation is the most frequent location for TICA formation. Up to 90% of reported TICA following blunt trauma are associated with underlying skull fractures (▶ Fig. 34.1 ).

Traumatic aneurysms have been described following iatrogenic injury and penetrating trauma. Several case reports have detailed TICA formation following endoscopic surgery, paranasal sinus surgery (▶ Fig. 34.2 ), skull base surgery, and ventriculostomy. Aneurysms following these procedures are generally the result of injury to the internal carotid, but less commonly secondary to insult of the ACA, middle cerebral artery (MCA), or basilar artery. The majority of TICAs are reported following blunt injuries. Of the TICAs following penetrating injury, it is has been observed that low-velocity injuries are more likely to lead to TICA formation as compared to high-velocity injuries.