Retro-Odontoid Intradural Synovial Cyst Decompression via Endoscopic-Assisted Far-Lateral Approach C1-C2 Hemilaminectomy Without Fusion: The Use of Intracranial Denticulate Ligament as Intraoperative Landmark

Abstract

Purely intradural retro-odontoid synovial cysts are rarely reported in neurosurgical literature, particularly in the absence of associated bony erosions. We present the case of a 57-year-old Native American male with a retro-odontoid synovial cyst and a history of chronic refractory neck pain that was adequately decompressed via an endoscopic-assisted far-lateral approach using a C1-2 hemilaminectomy, obviating the vertebral artery (VA) transposition, bony instability, and the need for instrumented bony fusion. The patient presented to our clinic with several months of refractory nuchal and cervical spine pain and crepitation affecting his activities of daily living (ADL). MRI findings revealed an intradural cyst at the level of C2 behind the odontoid process impinging on the medulla and causing early VA displacement. Both stereotactic neuro-navigation and microsurgical visualization aided in the manipulation of the endoscope and attaining the caudocranial working trajectory. The patient remained neurologically non-lateralizing postoperatively, similar to his preoperative status. This article highlights a less invasive surgical exposure with an endoscope-assisted caudocranial trajectory obtained by a limited unilateral hemilaminectomy to achieve the desired outcome.

Keywords: atlanto-axial cyst; endoscopy; intradural extramedullary mass; retro-odontoid cyst; synovial cyst.

Figure 1. (A) CT neck demonstrating mild focal hyperostosis behind the dens. (B) Sagittal and axial (C) MRI of the head and neck demonstrating spinal stenosis at C1-2 from intradural extramedullary mass (IDEM) (arrow) impinging on the spinal cord at the level of dens. (D, E) Artist's rendering of the location of the retro-odontoid intradural mass. (F) Postoperative sagittal and axial (G) MRI of a resected cystic portion of the tumor and reduced mass effect (arrow) on the brainstem

CT: computed tomography; MRI: magnetic resonance imaging

Figure 2. Intradural exposure demonstrated after C1-2 hemilaminectomy, with a close-up endoscopic view of the dura attachment after sacrificing the denticulate ligament

Figure 3. PRISMA flowchart showing the search strategy for current literature and article selection for analysis

Search function: "intradural atlantoaxial cyst", "retro-odontoid cyst", and "odontoid cyst" yielded 73 results initially PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analysis