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Background
Trauma to the internal carotid artery may present as a of range of findings from luminal irregularity to complete vessel transection, with an associated increase in morbidity and mortality with more severe injuries. One such injury that carries a high rate of complication is pseudoaneurysm formation along the internal carotid artery (ICA). These entities are prone to rupture, which may have dire consequences if not treated appropriately; thus, it is critical for the emergency radiologist to accurately diagnose and triage patients with this condition. In this educational exhibit, we present imaging from a patient with delayed presentation of a traumatic intracranial internal carotid pseudoaneurysm with associated carotid-cavernous fistulization 3 weeks after a motor vehicle accident to help illustrate diagnosis and management of this rare entity.

Educational Goals / Teaching Points
Review the anatomy of the extra-cranial and intra-cranial carotid arteries. Describe the range of traumatic injuries which may be seen along the carotid arteries and associated clinical presentations. Understand cross-sectional, sonographic, and angiographic findings indicative of traumatic injury to the carotid arteries. Review the surgical and endovascular management options available for treatment of clinically significant injuries to the carotid arteries.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Injury to the ICA can have dire neurologic consequences; with severe injury, permanent disability or death is common. Imaging findings of ICA injury may have a variable appearance across imaging modalities and demonstrate a delayed presentation in relation to the inciting trauma, such as in the case presented here. Computed tomographic angiography (CTA) is the imaging modality of choice to assess the entire intracranial and extracranial ICA. In this case, CTA performed immediately after trauma demonstrated slight heterogeneity at the genu of the intracranial ICA without focal luminal narrowing, felt to be secondary to streak artifact from the skull base. The patient underwent a magnetic resonance venogram (MRV) 3 weeks after the initial trauma to evaluate for possible venous thrombosis secondary to known skull base fractures and progressive right sided visual field defects; this exam incidentally noted a large saccular pseudoaneurysm arising from the right ICA. This finding was confirmed on repeat CTA and catheter directed angiography of the right ICA, with additional diagnosis of a traumatic carotid-cavernous fistula. Treatment was performed by coil embolization of the parent supraclinoid right ICA to obliterate flow to the pseudoaneurysm sac. Cerebral blood flow was preserved by collateral circulation.

Conclusion
The case presented demonstrates a specific case of traumatic injury to the ICA which led to development of an intracranial pseudoaneurysm with carotid-cavernous fistulization 3 weeks after the inciting trauma. Emergency radiologists must be aware of the ICA anatomy and findings suggestive of ICA injury to prevent severe morbidity and mortality in patients with head and neck trauma.