Basilar vasospasm diagnosis: investigation of a modified "Lindegaard Index" based on imaging studies and blood velocity measurements of the basilar artery.

BACKGROUND AND PURPOSE Numerous studies have shown that cerebral vasospasm is one of the leading causes of death and neurological disability after subarachnoid hemorrhage. Most of these studies, however, have focused on anterior circulation vessels. Since the introduction of the transcranial Doppler (TCD), increasing attention has been given to basilar artery (BA) vasospasm, especially in traumatic subarachnoid hemorrhage. As shown for the anterior circulation, however, the significance of elevated flow velocities (FVs) in the posterior vessels may be ambiguous, so vasospasm may not be reliably differentiated from hyperemia. The purpose of the present study was to evaluate the potential additional value of an intracranial/extracranial FV ratio in the posterior circulation to cope with this shortcoming of the TCD in the diagnosis of BA vasospasm. METHODS FV in the extracranial vertebral artery (VA) was measured in 20 healthy volunteers. Normative values of an intracranial/extracranial VA FV ratio (IVA/EVA) and a BA/extracranial VA FV ratio (BA/EVA) were calculated. Thirty-four patients with subarachnoid hemorrhage were then evaluated with TCD and CT angiography (CTA). The value of the IVA/EVA and BA/EVA ratios in the diagnosis and assessment of vertebrobasilar vasospasm was investigated. RESULTS The extracranial VA could be insonated in all subjects at depths ranging from 45 to 55 mm. The average FV for the extracranial VA was 26 cm/s. The ratios between intracranial and extracranial VA FVs were 1.6 on both sides, whereas the ratio between the BA FVs and the mean extracranial VA FVs was slightly higher at 1.7. Fourteen patients (41.2%) had CTA evidence of BA vasospasm. Vasospasm was severe in 7 patients, moderate in 1, and mild in the remaining. An FV threshold of 80 cm/s was indicative of BA vasospasm in 92.8% with 3 false-positive results that could be related to vertebrobasilar hyperemia. Comparative analysis between CTA and TCD findings showed that BA/EVA was >2 in all patients with BA vasospasm (100% sensitivity) and < 2 in all but 1 patient without BA vasospasm (95% specificity). Furthermore, the BA/EVA ratio showed a close correlation with BA diameter (r=-0.8139, P<0.0001) and was >3 in all patients with severe vasospasm. CONCLUSIONS The results of the present study showed that the BA/EVA ratio may contribute to an improved discrimination between BA vasospasm and vertebrobasilar hyperemia and enhance the accuracy and reliability of TCD in the diagnosis of BA vasospasm. Our data further suggest that the BA/EVA ratio may provide an approximation of vasospasm severity and help in identifying patients who are likely to suffer from hemodynamically significant vasospasm.