Basilar Invagination and Atlanto-Axial Dislocation

Abstract

Basilar invagination (BI) and chronic atlanto-axial dislocation (AAD) are the most common congenital anomalies of the CVJ, can occur combined and become symptomatic when produce a ventral cervicomedullary compression. The standard transoral approach (TOA) allows a satisfactory surgical exposure and decompression in more then 80% of patients with BI and AAD. In cases of limited mandibular excursion (i.e. interdental space ≤30 mm) and/or severe basilar invagination (odontoid tip projecting ≥20 mm above the Chamberlain’s line) with a resultant neural compression at the level of the nasopharynx, the endonasal endoscopic approach is an effective alternative option. In patients with tonsillar prolapse and basilar invagination, transoral decompression allows the ascent of cerebellar tonsils into the posterior fossa and the resolution of associated syringomyelia due to the restoration to normal of CSF flow at the CVJ level. The occurrence of acute or delayed spinal instability (occipito-atlantal, atlanto-axial, or occipito-atlanto-axial instability) after transoral decompression is invariably high and requires posterior fixation and fusion. In our experience, the single anesthesia transoral decompression and subsequent posterior fusion eliminate the risk of postoperative instability and allow to mobilize the patients as soon as possible. After an adequate learning curve and following the basic tenets of skull base surgery, the approach related-morbidity in standard TOA is less than 10%.