Background and purpose: Evaluation of vertebral artery (VA) with transcranial Doppler ultrasonography (TCD) is difficult due to anatomical variations of hypoplasia (HP) or aplasia (AP). TCD findings of HP or AP of VA are rarely known. Comparing with magnetic resonance angiography (MRA), we tried to evaluate characteristic findings of HP or AP of VA using TCD.
Methods: Consecutive healthy patients who underwent TCD and MRA were included. VA was classified as normal (NL), hypoplasia (HP), and aplasia (AP) according to MRA. TCD parameters of mean flow velocity (MFV), pulsatility index (PI), vertebral/basilar artery flow velocity ratio (VA/BA FVR), and asymmetry index (AI) of VA were compared between three groups.
Results: Four hundred and ten patients were included, and 298 patients (72.7%) were classified as NL, 98 (23.9%) as HP and 14 (3.4%) as AP. MFV, PI and VA/BA FVR of ipsilateral VA were not different between groups. However, MFV of contralateral VA and AI were significantly increased in HP and AP groups (p<0.001). AI was significantly different between the three groups (17.7% and 30.5%, p<0.001). Sensitivity and specificity for HP or AP were 20.5% and 90.9%, if AI over 40% were adopted as diagnostic criteria.
Conclusion: MFV of VA should be interpreted with caution for its frequent anatomical variations. Increased MFV of unilateral VA may indicate not only as ipsilateral stenosis, but also as contralateral HP or AP. AI over 40% is specific to predict unilateral HP or AP with clinical correlation.