Feasibility of the Far Lateral Suboccipital Approach to the Retroodontoid Region. How Much Bone Removal Is Truly Needed?

OBJECTIVE: The posterolateral extradural suboccipital approach can be used to reach the anterior epidural space and the retro-odontoid regions. The extent of necessary bone removal of the atlas vertebra (C1) has not yet been defined. We studied the changes in the size of the horizontal and vertical surgical windows using stepwise bone removal of C1. A representative case is shown. METHODS: The anatomical study was performed bilaterally on five Thiel-fixed human cadavers (mean age, 83.7 years). The surgical window (horizontal × vertical) required to access the retro-odontoid region via a posterolateral approach was measured for an intact C1 posterior arch, after a semicircular inferior partial resection of the C1 arch, after resection of the unilateral hemiarch of C1, and finally after drilling approximately 3 mm from the medial aspect of the lateral mass of C1. RESULTS: The intact C1 resulted in a very narrow surgical window of 6.3 mm × 9.7 mm (horizontal × vertical). The vertical window increased to a 13 mm after the semicircular inferior partial resection of the C1 arch and to 17.3 mm in the case of removal of the ipsilateral C1 posterior arch. The bone removal from the medial aspect of the C1 lateral mass resulted in a widening of the horizontal surgical window to 10.3 mm. The final size of the surgical window was 10.3 mm × 17.3 mm. The patient with severe kyphoscoliosis of the craniocervical spine was successfully operated on using odontoid and C1–2 facet osteotomies. CONCLUSION: If only the anterior epidural space or the base of the odontoid needs to be reached, the semicircular inferior partial resection of the C1 arch allows for an adequate surgical window. The tip of the odontoid could only be reached if the ipsilateral posterior arch is resected.