Expanded Endoscopic Endonasal Approach and Odontoidectomy for Atlantoaxial Synovial Cyst.

Introduction Synovial cysts of the atlantoaxial joint (AAJ) are rare lesions that may cause progressive spinal cord compression and cervical myelopathy. Surgical management of retro-odontoid pathology is challenging due to complex regional anatomy and proximity to critical neurovascular structures. Traditional approaches, including transoral and posterior transdural techniques, are associated with notable morbidity. The endoscopic endonasal approach (EEA) provides a minimally invasive alternative with direct access to the retro-odontoid space. We report an isolated AAJ synovial cyst treated with an endoscopic endonasal odontoidectomy as the sole anterior approach, highlighting technical refinements that optimized access to the retro-odontoid space. Case Description A 48-year-old woman with a history of C4 corpectomy and C3 to C7 anterior fusion presented with progressive neck pain and cervical myelopathy, secondary to a retro-odontoid cystic lesion causing spinal cord compression. She underwent an endoscopic endonasal odontoidectomy and lesion resection followed by posterior occipitocervical fusion. Surgical exposure was optimized through posterior septectomy and targeted drilling of the odontoid process to access the retro-odontoid space. Excision and adequate decompression of the spinal cord were achieved, and histopathology was consistent with synovial cyst. Conclusion The EEA allowed effective ventral decompression of the AAJ synovial cyst while minimizing morbidity associated with transoral and posterior transdural approaches. Strategic modifications to improve surgical angulation and maneuverability can overcome traditional limitations of the endonasal corridor. This approach represents a viable, minimally invasive option for select retro-odontoid pathologies while reducing trauma to oropharyngeal tissue and avoiding dural violation at the AAJ.