Hypoplastic vertebral artery: frequency and associations with ischaemic stroke territory

Background: In patients with posterior inferior cerebellar artery infarction ( PICAI) or lateral medullary infarction ( LMI), the ipsilateral vertebral artery is often hypoplastic and therefore at an increased risk of ischaemic stroke. Objective: To investigate the frequency and clinical relevance of hypoplastic vertebral artery ( HVA) in patients with ischaemic stroke with or without vertebral artery territory and in normal healthy people. Methods: 529 patients with ischaemic stroke, including vertebral artery territory infarction ( LMI or PICAI), were classified according to their stroke location ( 303 anterior circulation strokes ( ACS) and 226 posterior circulation strokes ( PCS)) by MRI. The frequency of HVA, defined as a diameter of ( 2 mm by magnetic resonance angiography, was measured in comparison with 306 normal healthy people. Results: 185 patients ( 35.2%) from the cohort had HVA ( 3.4%, bilaterally). Patients with PCS showed a higher rate of HVA than those with ACS ( 45.6% vs 27.1%, p, 0.001). The HVA frequency of those with ACS was similar to that of the normal group ( 26.5%). Of the 112 patients with vertebral artery territory stroke, 58 ( 51.8%) had HVA ( bilateral HVA in 10), and all of 48 showed ipsilateral HVA territory stroke. In 102 patients with vertebral artery territory stroke, classification of the ipsilateral vertebral artery as hypoplastic ( vs dominant or symmetric) tended to predict the involvement of multiple and extensive lesions, and a higher incidence of steno- occlusion ( p < 0.001). Conclusion: HVA is not rare in the normal population, and is frequent in patients with PCS. People with HVA may have a high probability of PCS, with atherosclerotic susceptibility and ipsilateral lesions in the vertebral artery territory.