What is the significance of fenestration in Computed Tomography Angiography (CTA) of the head and neck?

From the Guidelines

Fenestration of CTA of the head and neck should be performed using a biphasic protocol with an initial injection rate of 4-5 mL/second of iodinated contrast, followed by a 30-40 mL saline chaser at the same rate, to optimize visualization of specific vascular structures. The timing of contrast administration and image acquisition is crucial in evaluating vascular pathologies of the head and neck. According to the American College of Radiology (ACR) Appropriateness Criteria for penetrating neck injury 1, CTA of the neck is the preferred imaging procedure to evaluate the extent of injury in patients with clinical soft injury signs and in patients with hard signs of injury who do not require immediate surgical exploration.

Key Considerations for CTA Fenestration

• The use of bolus tracking with a region of interest placed in the aortic arch and a trigger threshold of 100-150 Hounsfield Units can help determine the optimal timing for image acquisition 1.
• Arterial phase imaging should begin approximately 5-8 seconds after the trigger threshold is reached, with scan direction from the aortic arch upward through the circle of Willis 1.
• Adjustments may be needed for patients with cardiovascular disease, with reduced injection rates of 2-3 mL/second for those with poor cardiac output 1.
• Proper fenestration is crucial because premature acquisition may miss arterial opacification, while delayed acquisition can result in venous contamination that obscures arterial pathology such as stenosis, aneurysms, or arteriovenous malformations 1.

Benefits of CTA in Penetrating Neck Injury

• CTA has high sensitivity and specificity for detecting vascular and aerodigestive injury, with a sensitivity of 100% and specificity of 97.5% in a prospective study 1.
• The use of CTA can help reduce the need for surgical neck exploration and negative neck explorations, as well as the use of catheter angiography and esophagography 1.
• CTA can also help identify patients who may benefit from endovascular or medical therapy, rather than surgical exploration 1.

Limitations and Alternative Imaging Modalities

• Ultrasound (US) is limited in its use in patients with penetrating neck injury due to the effect of overlying adjacent soft-tissue injury and limited evaluation of surrounding structures 1.
• MRI and MR angiography (MRA) are limited in the initial trauma setting due to the length of scanning and potentially critical nature of the patient's condition 1.
• Catheter-based arteriography may be useful for further evaluation when there remains clinical concern for vascular injury despite a normal or equivocal CTA of the neck 1.

From the Research

Fenestration of CTA of Head and Neck

• Arterial fenestrations are a benign entity arising from a failure of fetal fusion, and they can be misinterpreted as carotid webs or dissections on CTA imaging 2.
• The prevalence of arterial fenestrations in the head and neck is 0.4% on CTA studies, with 7 cases found in a total of 1800 head and neck CTAs 2.
• Fenestrations can be associated with non-atherosclerotic calcification, pseudoaneurysm, or thrombosis, but these associations are rare 2.
• Basilar artery fenestration is a common site of fenestration, and it can predispose a patient to posterior aneurysm formation and increase the complexity of surgical anatomy 3, 4.
• Endovascular treatment is a safe and efficient option for treating basilar artery fenestration aneurysms, and a detailed understanding of the aneurysm morphology and its relation to the fenestration is crucial for treatment planning 3.

Characteristics of Fenestration

• Basilar artery fenestrations can be classified into different types, including Type I, Type II, Type III, and Type IV, based on their morphology and location 4.
• The coexistence of fenestration and aneurysm is uncommon, with a frequency of 15% in CTA examinations, but the incidence of ipsilateral aneurysm is only 2.5% 5.
• Fenestrations can be detected by computed tomography angiography (CTA), which offers a rapid and non-invasive means of evaluating the vasculature of the head and neck 6, 4, 5.

Clinical Significance

• Differentiating arterial fenestrations from carotid webs and dissections is important for clinical management, as these entities have different treatment options and outcomes 2.
• The presence of fenestration can increase the risk of aneurysm formation, particularly in the posterior circulation, and therefore, it is essential to monitor patients with fenestration for aneurysm development 3, 4.