case_images: PMC8576039_01
case_images: Magnetic resonance angiography (MRA) shows the bilateral vertebral arteries (VAs) merging into the basilar artery, and the left VA is dominant (A). Digital subtraction angiography (DSA) shows the right posterior inferior cerebellar artery (PICA) originating and coursing into the spinal canal between the atlas and the axis (B). The left VA proceeds into the spinal canal at the atlas-axis level (C). On dynamic DSA at 45  leftward head rotation (D), the right VA was compressed at the V3 segment. At 60  leftward head rotation (E), the right PICA becomes occluded in addition to severe compression of the right VA. Dotted line: trace of axis; *: right PICA; arrow: compressed right VA; arrowhead: occluded right PICA. A-P, anterior-posterior.
case_images: fneur-12-756838-g0001.jpg
case_images: PMC8576039_01_fneur-12-756838-g0001.jpg
case_images: F1
case_images: Magnetic resonance angiography (MRA) showed no pathological abnormality; he exhibited bilateral VAs merging into the basilar artery, and the left VA was dominant (Figure 1A). However, digital subtraction angiography (DSA) showed variants of the bilateral vertebral arteries; the right PICA originated from the right VA at the atlas-axis level and ran vertically into the spinal canal (Figure 1B), whereas the left VA ran into the spinal canal at the atlas-axis level without passing through the atlas' foramen transversarium (Figure 1C). Leftward head rotation at 45  did not induce dizziness, but dynamic DSA showed stenosis of the right VA at the level of the axis (Figure 1D). At 60  head rotation, which induced dizziness, occlusion of the right PICA was revealed (Figure 1E).
case_images: Computed tomography angiography (CTA) with leftward head rotation shows the right PICA and VA as compressed (A). The PICA was compressed in the narrow space surrounded by the posterior arch and lateral mass of the atlas and the superior articular facet of the axis (B: sagittal image of the atlas; C: axial; D: coronal). The right VA was compressed by the anterior wall of the transverse foramen at the axis (E: sagittal image of the axis). White arrowhead: PICA, black arrowhead: compressed PICA, arrow: compressed VA, *: occipital condyle, A: anterior, P: posterior.
case_images: fneur-12-756838-g0002.jpg
case_images: PMC8576039_01_fneur-12-756838-g0002.jpg
case_images: F2
case_images: Computed tomography angiography (CTA) on leftward head rotation showed that the PICA was severely compressed in the narrow space surrounded by the atlas and axis, and that the right VA was compressed at the axis level (Figure 2).
case_images: Operative view (A) shows a dissected right PICA (arrowhead), C2 nerve root (*), and decompressed right VA (arrow) after resecting part of the atlas (dotted line: resected atlas). Postoperative MRA at 60  leftward head rotation (B) shows no compression of the right PICA and VA.
case_images: fneur-12-756838-g0003.jpg
case_images: PMC8576039_01_fneur-12-756838-g0003.jpg
case_images: F3
case_images: The dizziness was restrictive to the patient's daily activities; therefore, he underwent surgery to decompress the right PICA and VA via a posterior approach (Figure 3A). On postoperative MRA at 60  leftward head rotation, compression of the right VA and PICA had disappeared (Figure 3B).