Retro-odontoid Intradural Synovial Cyst Decompressed via an Endoscope-Assisted Far Lateral Approach C1-C2 Hemilaminectomy without Fusion: Use of Denticulate Ligament as Intraoperative Landmark

Background: Purely intradural (retro-odontoid) synovial cysts are rarely reported in neurosurgical literature, especially with no bony erosions. We present the case of a middle aged male with a retro-odontoid cyst associated with a history of chronic refractory neck pain, decompressed via an endoscope-assisted far lateral approach C1-C2 hemilaminectomy without fusion.

Case Summary: A 57-year-old male presented to our clinic with a several month history of neck, shoulder, and hand pain. Magnetic resonance imaging (MRI) findings revealed an intradural cyst at the level of C2 behind the odontoid process, which impinged on the medulla and caused vertebral artery displacement. The differential diagnosis of a cystic meningioma, chordoma and ecchordosis physaliphora was entertained. Considering the patient's progressively worsening symptoms and interval growth in size of the cyst and increasing mass effect, it was decided to decompress the cyst surgically and obtain histological diagnosis. A far lateral approach with endoscopic assistance was employed, without transposition of vertebral artery segment over C1. C1-C2 hemilaminectomy without fusion was employed for access and denticulate ligament served as an intraoperative surgical landmark. There was a thick walled intradural cyst containing greenish yellow fluid with waxy cyst contents,, encountered after cutting the first denticulate ligament. The final pathology was reported as a synovial cyst. The patient remained neurologically intact, same as preoperative status. This article highlights the surgical trajectory obtained by a left hemilaminectomy and endoscopic guidance.

Conclusion: This case represents a rare case of retro-odontoid synovial cyst with review of literature on surgical approaches with and without fusion. The utility of planning surgical trajectory using Stealth neuronavigation and endoscopic assisted “fish eye” view visualizing contralateral aspect of the lesion are well-illustrated. An endoscope-assisted far lateral approach using C1-C2 hemilaminectomy without fusion is demonstrated using first denticulate ligament as the landmark.