Diagnosis of basilar artery vasospasm.

Abstract

To the Editor: I read with interest the recent article in Stroke by Soustiel et al1 regarding improvement in the diagnosis of basilar artery vasospasm by transcranial Doppler (TCD) sonography. The article describes normative and patient-derived data pertaining to a BA/EVA ratio, defined as the ratio between the highest recorded basilar artery (BA) flow velocities (insonation depth >80 mm) and the average of the flow velocities from the 2 extracranial vertebral arteries (EVA) (insonation depth 45 to 55 mm). The purpose of the study was to learn if this ratio could help discriminate between BA vasospasm and BA hyperemia, given that BA flow velocities may be difficult to interpret in this setting.2,3⇓ In fact, a previous study2 showed that 5/6 false-positive TCD examinations for BA vasospasm were of unknown cause. It has recently been hypothesized that this observation may be due to dysautoregulation or hyperemia.3–5⇓⇓ The present authors showed (1) a strong linear correlation between BA diameter measured by computed tomographic angiography and the BA/EVA ratio, (2) that a BA/EVA ratio >2 has 100% sensitivity for BA vasospasm, and (3) that a BA/EVA ratio >3 identified severe angiographic BA vasospasm. While these data are useful for the interpretation of BA flow velocities patients with subarachnoid hemorrhage, there are a number of methodologic concerns6 about the work of Soustiel et al.1 First, the definition of the BA/EVA ratio bears a striking resemblance to the Vba/Vva ratio described 5 years ago.7 In that article,7 normative data and patient-derived data using the same rules for insonating the vessels and calculation of the so-called posterior circulation flow index5 were presented. Using a Vba/Vva ratio >2.5, the specificity of TCD for BA vasospasm was substantially improved from 42.3% to 87.5%, suggesting that the …