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

Abstract

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.

Keywords: atlantoaxial dislocation; atlantoaxial instability; os odontoideum; posterior circulation ischemic stroke; vertebral artery.

FIGURE 1

Angiography images over the past 4 years. (A) Anteroposterior view of the left VA angiograms during the second episode, demonstrating a winding “string‐of‐beads” change (arrow) in the V3 segment. (B) Black blood sequence, showing a mural thrombus formation (arrow). (C) The follow‐up magnetic resonance angiography after conservative treatment, showing complete absorption of the thrombosis in the left VA. (D) Anteroposterior view of the left VA angiogram during the third episode, demonstrating thrombosis reformation (arrow) in the V3 segment.

FIGURE 2

Preoperative radiographic images. (A) A transverse view of T2‐weighted MRI, showing old cerebellar infarcts in bilateral PICA territory and left SCA territory. (B) Sagittal view of T2‐weighted MRI showing OO and myelopathy (arrow) at C1 level. (C) Black blood sequence showing lateral AAD (red arrow) and compressed left VA (yellow arrow). (D) CT sagittal multiplanar reconstruction with OO. CT coronal multiplanar reconstruction in pre‐traction (E) and post‐traction (F) states compares the alignment of the atlas (red arrow) and axis (yellow arrow). (G,H) Flexion‐extension lateral X‐rays of cervical spine revealing AAI with OO.

FIGURE 3

Postoperative follow‐up images at 6 months. (A,B) Anteroposterior and lateral x‐rays showing posterior atlantoaxial fixation and fusion. (C) MRI showing satisfactory posterior decompression (arrow) of the spinal cord. (D) CT sagittal multiplanar reconstruction showing a solid union of the grafted autologous iliac bone (arrow). (E) CT angiography coronal multiplanar reconstruction showing the release of compression of the left VA (arrow).

FIGURE 4

(A,B) 3D‐printed cervical model, illustrating the leftward dislocation of the atlas relative to the axis and the positions of VAs in relation to the atlas. The left VA is compressed by the inferior edge of the lateral mass (B, arrow).