Surgical Management of Cervical Myelopathy Due to Congenital Synostosis at the Craniovertebral Junction: Vertebral Artery Anomalies and Full-Endoscopic Retropharyngeal Odontoidectomy in a Case Series of Five Patients

Congenital synostosis at the craniovertebral junction (CVJ), including C1 assimilation and C2-C3 fusion, can lead to cervical myelopathy due to adjacent segment stenosis or instability. These anomalies are rare and frequently associated with vertebral artery (VA) variations, which complicate surgical planning and instrumentation. This case report describes five patients who developed cervical myelopathy associated with congenital CVJ synostosis and were surgically treated at our institution between 2019 and 2023. Preoperative imaging, including computed tomography (CT), magnetic resonance imaging (MRI), and CT angiography, was used to evaluate bony anomalies and VA morphology. Posterior decompression and fusion were performed under navigation guidance, with screw selection tailored to the individual anatomy. Among the five patients (mean age, 74.8 years), three had C1 assimilation, four had C2-C3 fusion, and two had both. VA anomalies, such as high-riding VA and unilateral hypoplasia, were present in all patients with C2-C3 fusion, requiring modified screw trajectories to prevent vascular injury. Three patients underwent full-endoscopic retropharyngeal odontoidectomy for persistent ventral compression after posterior fixation. All patients showed postoperative neurological improvement, and no VA injury or screw malposition occurred. Imaging confirmed sufficient decompression and appropriate fixation. Congenital CVJ synostosis with associated VA anomalies presents unique surgical challenges. Preoperative vascular imaging and intraoperative navigation are essential for safe fixation, and full-endoscopic retropharyngeal odontoidectomy offers a minimally invasive and effective option for anterior decompression in selected cases.