Microsurgical Unroofing to Secure a Safe Corridor for C1 Screws in Bilateral Ponticulus Posticus: A Case Report

Ponticulus posticus (PP) is a bony bridge arising from the posterior arch of C1 toward the superior articular process or lateral mass; when complete, it forms an arcuate foramen over the C1 vertebral artery (VA) groove and may convert the VA path into an osseous canal. This anatomy can narrow the usual corridor for C1 lateral mass screw (LMS) insertion. We report a 68-year-old man who sustained an upper cervical cord injury (ASIA Impairment Scale grade [AIS] B) after a fall. Computed tomography (CT) revealed continuous ossification of the posterior longitudinal ligament and anterior longitudinal ligament from C2 to T1, and magnetic resonance imaging showed canal stenosis due to a retro-odontoid pseudotumor with intramedullary signal change. Dynamic flexion radiograph demonstrated an atlas-dens interval of 5.6 mm and a space available for the spinal cord of 15.5 mm, while three-dimensional computed tomographic angiography identified bilateral complete PP with an aberrant VA course and no symptoms of vertebrobasilar insufficiency. After C1 laminectomy, the arcuate bony bridge was microsurgically unroofed with a 3-mm high-speed burr, enabling direct visualization and protection of the VA with neurosurgical sheets and a Penfield dissector; unroofing was complete on the left and partial on the right based on the bony bridge morphology and the VA exit point. An intraoperative navigation system confirmed screw entry points and trajectories, allowing placement of C1 screws. Immediate postoperative CT confirmed appropriate screw positions. Postoperative vascular imaging was not performed. At three months, the patient's neurological status improved to AIS C, which indicates motor-incomplete spinal cord injury, with no implant-related complications. In bilateral complete PP, the risk of VA injury with C1 LMS has led to divergent recommendations ranging from avoidance to conditional use with protective techniques. Microsurgical unroofing placed the VA under direct visualization and protection, and navigation verified a controlled corridor, supporting intraoperative adjustments in complex C1-2 anatomy. In this setting, microsurgical unroofing with navigation permitted C1 LMS placement under direct VA visualization and protection and may be a reasonable option when a controlled corridor can be created in selected patients.