Unusual Case of C2 Subisthmic Vertebral Artery with Atlantoaxial Dislocation: Persistent Second Cervical Intersegmental Artery

Abstract

The vertebral artery (VA) may have an anomalous course in patients with congenital atlantoaxial dislocation. In such cases, the artery crosses the C1-C2 joint posteriorly. These cases need thorough evaluation of the VA course to avoid its injury during posterior reduction and fusion of C1-C2. We describe for the first time an unusual subisthmic course of VA in a case of congenital irreducible atlantoaxial dislocation (AAD). The surgical implication and possible embryology of such an anomaly have been highlighted. A 25-year-male diagnosed with congenital AAD presented with spastic quadriparesis. Radiology showed irreducible AAD with oblique C1-C2 facet joints. The computed tomography angiogram showed the right VA traversing beneath the isthmus of atlas. The joint was opened, drilled, manipulated, and fused with a C1 lateral mass and C2 pedicle screw. The C2 isthmus was defined, and the C2 pedicle screw was inserted to prevent injury to the VA. The patient gradually improved and was doing well at his 6-month follow-up. The subisthmic variant of the VA may be the result of persistent C2 intersegmental artery. The presence of a subisthmic VA increases the chance of injury while inserting transarticular or C2 pars screw and warrants insertion of direct pedicle screw.