RESUMO
CASE: We treated an 87-year-old woman with noninflammatory retro-odontoid pseudotumor induced by atlantoaxial instability (AAI) using only a Philadelphia collar. Because of perioperative risk factors, fusion surgery was canceled; nevertheless, the neurological symptoms improved gradually. After 11 months of nonoperative treatment, the follow-up magnetic resonance imaging demonstrated that the pseudotumor's size was obviously diminished. Orthosis was applied for 2 years, and after its removal, the pseudotumor's size remained the same at the final 7-year follow-up. CONCLUSIONS: External orthosis is one treatment option for pseudotumor with AAI, especially in patients with significant comorbidities for whom surgical procedures are relatively contraindicated.