Periodontoid pseudotumor with cranial retroclival extension and brainstem compression in a patient with rheumatoid arthritis: illustrative case.

backgroundPeriodontoid pseudotumor is a nonneoplastic mass arising around the odontoid process and is most commonly associated with chronic atlantoaxial instability in inflammatory and noninflammatory conditions. Although traditionally managed with direct anterior resection, increasing evidence suggests that posterior stabilization may promote lesion regression by addressing the underlying biomechanical driver. OBSERVATIONS: A 73-year-old male with a history of rheumatoid arthritis was admitted to the authors' institution with a history of gait instability and vertigo. Contrast-enhanced MRI of the cervicomedullary junction revealed a retro-odontoid cystic mass with significant cranial extension into the retroclival region and compression on the lateral recess of the fourth ventricle. The patient underwent a C1-2 arthrodesis with the Magerl technique and decompression of the posterior arch of C1. Marked regression of the periodontoid mass was observed on 3-month postoperative MRI, along with significant cervicomedullary junction decompression. LESSONS: In carefully selected patients with radiological evidence of chronic atlantoaxial instability and favorable C1-2 anatomy, posterior stabilization may represent an effective primary strategy for managing periodontoid pseudotumor, even in cases with cranial extension. This approach may mitigate the morbidity associated with anterior mass resection, although its generalizability is limited by the single-case design and short-term follow-up. https://thejns.org/doi/10.3171/CASE26169.