Atlantoaxial instability and retroodontoid mass--two case reports.

Two relatively elderly male patients (61 and 78 years) suffered moderately severe trauma to the head 1 and 3 years, respectively, prior to presentation with progressive quadriparesis and neck pain. Investigations revealed retroodontoid ligamentous hypertrophy and subtle mobile atlantoaxial dislocation. Following atlantoaxial fixation, both patients showed remarkable and sustained neurological improvement. These cases provide further evidence that retroodontoid ligamentous hypertrophic mass lesion could be secondary to instability of the atlantoaxial region.