Intradural extraneural bilobate ganglion cyst of the atlanto-occipital joint compressing the hypoglossal nerve.

Ganglion cysts (ganglia) are benign lesions of the soft tissue arising in the periarticular space. We present a 54-year-old woman with a 5-month history of headache and weakness of the tongue with deviation to the left side who had a rare extraneural intradural bilobate ganglion cyst of the atlanto-occipital joint compressing the hypoglossal nerve. An MRI showed a bilobate cystic lesion in the premedullary cistern on the left side at the level of the hypoglossal canal. This lesion was removed using a lateral suboccipital approach in the semi-sitting position with removal of the C1 hemiarch. The lesion proved to be a ganglion cyst on histopathology. Intracranial juxtafacet (ganglion and synovial) cysts compressing the hypoglossal nerve should be considered in the differential diagnosis with other lesions of this region. Although there was no recurrence at 30-month follow-up, there was no significant improvement of the tongue weakness. We describe our surgical strategy and discuss the pathogenesis of the cyst.