5.1 Goals

1. 
   

   Understand the epidemiology and pathophysiology of traumatic intracranial aneurysms (TICAs).

   
   
2. 
   

   Review the literature to understand the various types of TICAs and their clinical presentations.

   
   
3. 
   

   Critically analyze the timing and role of computed tomography angiography (CTA) versus catheter angiogram in diagnosis and management of TICA.

   
   
4. 
   

   Review the literature for various treatment options currently available for the treatment of TICAs.

5.2 Case Example

5.2.2 Treatment Plan

The patient was treated with endovascular coiling to occlude the aneurysm as well as the segment of the right internal carotid artery (ICA) that incorporated the aneurysm. The aneurysm neck was deemed too wide and the aneurysm likely too fragile to treat using intrasaccular coils alone (Fig. 5.2a). Stent or flow diverter placement was felt to be suboptimal due to the need for antiplatelet therapy in the setting of the patient’s extensive intracranial blood and concomitant injuries. The patient tolerated the occlusion due to the presence of collateral flow from the contralateral ICA (Fig. 5.3b).

5.3 Case Summary

1. 
   

   What is the pathophysiology of traumatic intracranial aneurysms (TICAs)?

   
   

   TICAs are rare and account for< 1% of all cerebral aneurysms. ¹ They are reported to occur in 3.2% of civilian penetrating craniofacial injuries ² and in 42% of patients with gunshot wounds and missile head injuries. ³ They are more commonly seen in patients younger than 18 years. ^{1 , 4 , 5} This is possibly secondary to higher rates of traffic accidents and other trauma in this age group. The etiology can be variable and can range from seemingly trivial head injury to severe penetrating head injury. They are associated with severe mortality and morbidity when left untreated. ⁶

   
   

   Histologically, they can be classified into true, false (pseudoa-neurysms), and mixed aneurysms. ⁷ True aneurysms occur either due to direct impact or indirect transmission of force to the vessel wall, leading to an area of focal vessel weakness. Further flow dynamics across this weak wall leads to the formation of an aneurysm with the adventitia intact over it. False aneurysms, otherwise known as pseudoaneurysms, are far more common ^{4 , 7} and are due to rupture of all three layers of the vessel wall and formation of a contained hematoma. This leads to the formation of a false lumen and persistent flow into the false lumen which creates an aneurysmal dilatation. ^{4 , 8 , 9} Pseudoaneurysms are usually associated with penetrating or stab injuries. Mixed aneurysms are true aneurysms that have a contained rupture and subsequently form a pseudoaneurysm. The term “mixed aneurysms” are also occasionally used interchangeably with dissecting aneurysms. ^{10 , 11}

   
   
2. 
   

   What are the common sites of TICAs?

   
   

   Although TICAs are seen in both the anterior and posterior circulations, they are predominantly found in the anterior circulation and are more frequent in the distal cerebral branches. The most frequent sites are the peripheral branches of the middle cerebral artery (MCA), followed by the branches of the pericallosal artery. ^{12 , 13} These are usually associated with penetrating injuries, in which the missile impact has scattered numerous fragments of bone or metal in diverging trajectories. ⁸ Pseudoaneurysms can also be associated with closed head injuries and are caused secondary to shearing forces. One common site in children is the pericallosal aneurysm formed by the impact of the pericallosal artery against the falx margin. ^{8 , 14} TICAs on more proximal intracerebral arteries are commonly located in the supraclinoid ICA. ¹⁵

   
   

   The clinical presentation of TICAs can vary based on the location of the aneurysm. Supraclinoid TICAs can present with massive subarachnoid hemorrhage, delayed intracerebral hemorrhage, or progressive cranial neuropathies. ^{4 , 16 , 17} The average time from trauma to aneurysmal hemorrhage is approximately 21 days, and these lesions carry a mortality of almost 50%. ^{7 , 17} Infraclinoidal aneurysms often present as massive or recurrent epistaxis, cranial neuropathies, diabetes insipidus, or headaches. ^{18 , 19 , 20 , 21} Patients with distal branch TICAs usually present with delayed ICH. They can also present with seizures, can be diagnosed incidentally on routine radiographic follow-up, or in the evaluation of patients with growing skull fractures. ^{22 , 23}

   
   
3. 
   

   Do TICAs vary based on the mechanism of injury?

   
   

   Blunt trauma is a frequent cause of TICAs in children. The cranium is softer and the relatively mobile cerebral content is more prone to shearing forces which may cause greater harm to the delicate vessels. ^{4 , 24} Another proposed mechanism is arterial injury due to cranial base fracture, which can result in the development of an intracavernous aneurysm, similar to traumatic carotid-cavernous fistula (CCF) development. ^{7 , 23} These aneurysms usually present in a delayed fashion. TICAs can also develop as a result of missile or gunshot injuries. These present commonly on the distal branches of the MCA and are a result of full-thickness tear in the vessel wall due to the fragments. They present with recurrent bleeding and ICH. These patients generally tend to be sicker due to associated brain injury, and therefore, one should have a low threshold for screening these patients with an emergent angiogram. ^{3 , 26}

   
   
4. 
   

   What is the best timing of doing a cerebral angiogram to diagnose TICAs?

   
   

   CT is a widely used primary screening tool in patients with a traumatic brain injury, but it has a very low sensitivity for cerebrovascular injuries. Neurological deterioration due to unexplained ICH, massive epistaxis, and new cranial neuropathies should raise a suspicion for TICAs and warrant further investigation. ^{4 , 7} CTA is a noninvasive tool that is helpful in detecting vascular lesions. It has the added benefit of providing vessel wall information as compared to conventional angiography. It is, however, important to recognize that CTA is particularly inaccurate in aneurysms 5 mm or smaller and for those in the region of the anterior communicating artery. ^{7 , 27}

   
   

   Digital subtraction angiography (DSA) remains the gold standard diagnostic modality for intracranial aneurysms. ^{27 , 28} DSA generates high-resolution images of up to 0.1 to 0.2 mm and provides two-dimensional projection images, which is often enhanced by rotational angiography with three-dimensional image reconstruction, which appears to enhance its sensitivity and specificity. ²⁹

   
   

   There are currently no existing guidelines for the timing of angiography in TICAs. Isolated case reports and some case series have previously reported that most aneurysms after blunt traumatic injury present in a delayed fashion and suggest that the first angiography should be performed approximately 10 days to 2 weeks after the injury to avoid missed diagnoses. ^{7 , 8 , 9 , 30} However, the immediate risk of rupture is much higher in penetrating brain injuries, and there is a higher chance of harboring a pseudoaneurysm in these patients. ^{31 , 32} Therefore, a more emergent angiography as well as follow-up angiography 2 weeks later may be reasonable. Of course, patients with subarachnoid hemorrhage are at an increased risk for cerebral vasospasm, and repeat angiography at an earlier time interval may be necessary if signs and symptoms of vasospasm arise, with additional attention paid to investigating for the interval development of a pseu-doaneurysm.

   
   
5. 
   

   What are the various treatment modalities available for TICAs?

   
   

   Conservative management of TICAs has a reported mortality of 41%. Thus, most cases should be treated, either with open surgery or endovascular methods. The treatment of far distal aneurysms can typically be successfully managed with endovascular occlusion of the parent artery, either with coils or liquid embolic agents. In select cases, coiling of the aneurysm with preservation of the parent vessel may be possible; however, if a pseudoaneurysm is suspected, this is generally avoided. ³³

   
   

   The advent and subsequent improvement of flow divert-ers have also made treatment of more distal aneurysms with parent vessel preservation feasible using flow diversion. ³⁴ This may be particularly attractive for patients in whom it is felt that vessel sacrifice would not be tolerated, or when the aneurysm is discovered in a delayed fashion without an acute rupture. Delayed presentation often negates many of the concerns of using antiplatelet therapy that exist in the acute setting. Flow diversion can be considered in acutely ruptured aneurysms; however, the risks of antiplatelet therapy must be considered again. One must remember that flow diversion does not typically occlude an aneurysm immediately, and therefore, it may not be ideal for particularly fragile or actively bleeding aneurysms.

   
   

   Open surgery may increase the possibility of clipping the aneurysm with preservation of parent vessel but involves longer anesthesia duration, bleeding risks, and possible difficult dissection secondary to dense adhesions or brain swelling in the setting of trauma. However, curative surgical treatment, particularly of a pseudoaneurysm, may require trapping and sacrifice of the injured segment. In this case, endovascular occlusion is likely equally effective as open surgical ligation. If it is felt that the patient is unlikely to tolerate parent vessel sacrifice, bypass in combination with aneurysm trapping is an option (i.e., superficial temporal artery bypass for an MCA aneurysm or A3-A3 bypass for anterior cerebral artery aneurysms). Given that many of these lesions are a result of trauma, including penetrating injuries, the planned bypass vessel may also be injured and should be identified prior to surgery. Proximally located aneurysms are perhaps more technically challenging to treat, largely due to the greater territory at risk for hypoperfusion and subsequent stroke, should occlusion be required. Surgical options usually require sacrificing the parent vessel as reconstructing the parent vessel when a pseudoaneurysm is present is fairly risky and with low likelihood of success. When time permits, a thorough evaluation using balloon test occlusion can be done to test the collateral circulation. If the patient passes the balloon test occlusion, endovascular sacrifice of the artery may be reasonable. If occlusion is not felt to be a tolerated option, surgical options are generally limited to parent vessel sacrifice with high flow bypass or complex reconstruction of the vessel with a series of clips or wrapping which may be associated with high morbidity. Endovascular treatment options that preserve the parent artery may include coiling or placement of a stent graft/ covered stent. ³³ More recently, flow-diverting stents have been reported as useful and relatively safe in the treatment of carotid pseudoaneurysms. ³⁵ Again, it is important to note that placement of stents requires antiplatelet therapy, and the risks and benefits must be weighed carefully in the acute trauma setting. The initiation of antiplatelet therapy is much less of a concern for traumatic aneurysms that are seen in a delayed fashion and have not bled. However, as experience accumulates, flow diversion has become the treatment of choice for TICAs in many centers, even in the setting of acute bleed.