Atlanto-axial instability secondary to solitary eosinophilic granuloma of C2 in a 12-year-old girl.

Involvement of the axis by solitary eosinophilic granuloma is rare. We report a 12-year-old girl who presented with a unifocal eosinophilic granuloma of C2 that resulted in a pathologic fracture and atlanto-axial subluxation. She had no other skeletal or systemic manifestations of histiocytosis X. She was successfully treated with posterior spinal fusion and transoral excisional biopsy. Because solitary lesions may mimic malignant tumors, biopsy is advised in atypical cases. The prognosis for solitary eosinophilic granuloma is almost always favorable in terms of symptomatic improvement and restoration of vertebral height.