Cervical internal carotid artery fenestration: a rare cause of lumen "dissection''.

Purpose: To highlight the clinical and diagnostic importance of correctly identifying cervical internal carotid artery fenestration (fcICA), an extremely rare vascular anomaly, and to present a case where fcICA was initially misdiagnosed as a dissection in a patient with fibromuscular dysplasia (FMD).

Methods: A 47-year-old woman with pulsatile tinnitus underwent computed tomography angiography (CTA) and digital subtraction angiography (DSA) to differentiate between fenestration and dissection of the internal carotid artery.

Results: CTA revealed a fusiform dilatation of the distal C1 segment of the right internal carotid artery (ICA) with a linear filling defect, suggesting either fenestration or dissection. DSA confirmed the presence of a fenestrated right ICA segment composed of two symmetrical, smooth-walled limbs without a dissection flap, along with signs of FMD in the proximal vessel. The patient's symptoms were attributed to local flow perturbations induced by fcICA and FMD.

Conclusion: This case illustrates that fcICA can be a true anatomical variant rather than a result of dissection, emphasizing the need for accurate imaging and diagnosis to avoid unnecessary treatments. The coexistence of fcICA with FMD increases the risk of dissection, necessitating careful monitoring. The distinction between fenestration and pseudofenestration remains challenging, requiring comprehensive imaging and close collaboration between radiologists and vascular neurologists.