Persistent primitive lateral basilovertebral anastomosis-rethinking vertebrobasilar junction fenestration

To describe and analyze two rare cases of arterial rings at the vertebrobasilar junction (VBJ), likely representing persistent segments of the primitive lateral basilovertebral anastomosis (PLBVA), and to explore their embryological origin and clinical significance.

Two morphological arterial variants were identified during a retrospective review of computed tomography angiography (CTA) scans from 505 patients. Multiplanar reconstruction and three-dimensional volume rendering were used for anatomical characterization.

Two cases (0.4%) showed arterial rings at the VBJ, formed by a variant vessel arising from a vertebral artery and reconnecting with the basilar artery shortly after its origin. The vascular arrangements aligned with persistent segments of the PLBVA rather than true fenestrations. No significant asymmetry, hypoplasia, or dominance was seen in the vertebral or basilar arteries.

VBJ arterial rings may be embryological remnants of the PLBVA, a rare and often overlooked vascular variation. While usually asymptomatic, their presence can complicate radiologic interpretation and endovascular procedures. Proper identification through detailed CTA assessment is critical to avoid diagnostic errors and ensure procedural safety.