Staged dorsolateral decompression and posterior stabilization for severe ventral odontoid compression in basilar invagination: illustrative case.

backgroundBasilar invagination (BI) with ventral cervicomedullary compression remains surgically challenging. Although transoral and endoscopic endonasal odontoidectomy are established approaches, some anatomical variations may favor alternative surgical corridors. OBSERVATIONS: A patient with BI developed progressive quadriparesis after cervical trauma. Imaging demonstrated severe ventral cervicomedullary compression from a retroverted, left-lateralized odontoid process, displacing the cervicomedullary junction contralaterally. CT angiography revealed absence of the left vertebral artery (VA) and medial deviation of the left internal carotid artery (ICA). Because the odontoid was significantly lateralized, causing contralateral displacement of the cervicomedullary junction, and was located behind the ICA, with absence of the ipsilateral VA, ventrolateral decompression was performed through a modified left dorsolateral extradural lateral inferior transcondylar (ELITE) approach. Posterior craniocervical fixation and fusion were subsequently performed. The patient experienced neurological improvement with satisfactory radiographic decompression. LESSONS: Careful evaluation of the direction of odontoid displacement and surrounding vascular anatomy is critical in selecting the surgical corridor. In selected patients with a significantly lateralized odontoid and off-midline ventral cervicomedullary compression, a modified dorsolateral ELITE approach may provide a safe and direct alternative to conventional midline anterior approaches. Medial ICA displacement and absence of the ipsilateral VA further facilitated the lateral surgical corridor. https://thejns.org/doi/10.3171/CASE26747.