Vertebral Artery Dissection and PICA-Territory Stroke Associated with Chronic Atlantoaxial Structural Abnormality: A Case Report.

Upper cervical structural disease can alter vertebral artery biomechanics, although a mechanical contribution cannot be established by anatomical proximity alone. We describe an older woman with seronegative inflammatory arthritis and chronic atlantoaxial abnormality who developed abrupt vertigo, nausea, and inability to walk despite a National Institutes of Health Stroke Scale (NIHSS) score of 0. Computed tomography angiography (CTA) demonstrated left V3 vertebral artery dissection with pseudoaneurysmal dilation at the craniovertebral junction. Magnetic resonance imaging (MRI) showed a dominant acute left posterior inferior cerebellar artery (PICA)-territory infarction. Cervical imaging demonstrated atlantoaxial deformity, pannus-like peri-odontoid tissue, and a C1 arch abnormality adjacent to the affected V3 segment. Echocardiography and inpatient telemetry did not identify an embolic source. Anatomical colocalization of the C1-C2 abnormality and V3 lesion, together with the ipsilateral PICA infarction, suggests a possible mechanical contribution to the dissection, with subsequent artery-to-artery thromboembolism to the cerebellum. Dynamic compression was not demonstrated; spontaneous dissection, intracranial atherosclerosis, and occult embolism remain alternative or additional mechanisms. The patient received dual antiplatelet therapy followed by aspirin, statin therapy, and rehabilitation. This case emphasizes the limitations of the NIHSS in posterior circulation stroke and the importance of evaluating the craniovertebral junction when a V3 lesion occurs near upper cervical structural disease.