Posterior Circulation Ischemic Stroke From Atlantoaxial Instability and Lateral Dislocation due to Os Odontoideum: Case Report and Review of Literature.

Background: Strokes in young individuals often stem from unusual causes. Posterior circulation ischemic stroke caused by vertebral artery insufficiency due to atlantoaxial instability or dislocation is rare. We present a case of posterior circulation ischemic stroke due to an unstable os odontoideum and review the current literature. The clinical features and imaging manifestations are described to promote awareness of etiology, early diagnosis, and assessment.

Case Presentation: A 24-year-old male presented with recurrent right-sided limb numbness and weakness and cerebellar ataxia due to posterior circulation ischemic stroke. The work-up revealed thrombosis reformation in the tortuous left vertebral artery. It is noteworthy that the patient developed compression and chronic damage of the vertebral artery secondary to atlantoaxial instability and lateral dislocation due to an os odontoideum. He underwent antiplatelet and anticoagulant therapy, cervical traction, and posterior atlantoaxial screw fixation and fusion with iliac crest autograft. The postoperative course was uneventful. At 6-month follow-up, the patient had a solid fusion mass and rigid stability of the atlantoaxial joint without neurologic deficits or ischemic sequelae.

Conclusions: For unexplained posterior circulation ischemic stroke, it is important to consider unstable os odontoideum as a potential etiology, especially in pediatric and young adult male patients. Atlantoaxial instability and dislocation with os odontoideum, especially when occurring laterally, may cause insufficiency of the vertebral artery and subsequent posterior circulation ischemic strokes. The significance of lateral atlantoaxial dislocation in the genesis of vertebral artery injury and the necessity for specific positional imaging are emphasized.