Intraoperative Doppler to measure cerebrovascular resistance as a guide to complete resection of arteriovenous malformations

Intraoperative color Doppler ultrasound has been used to locate arteriovenous malformations (AVMs). We describe the use of spectral Doppler to measure flow resistance and resistive index (RI) of vessels around the nidus to distinguish feeding arteries from en passant and normal vessels. This is particularly helpful in small AVMs and aids in the identification of normal vessels and completeness of resection by ruling out persistent low RI flow. Seven patients with AVMs underwent resection. Spectral Doppler applied to the vessels in proximity to the AVM, along with calculated RI, was used to identify feeding arteries and draining veins. After presumed surgical resection of the AVM, pre-resection and postresection RIs were compared to identify residual AVM. Postoperative angiography was performed in all seven patients to confirm complete resection of the AVM. The mean pre-resection RI of vessels feeding the AVM was 0.34 (+/-0.01). In five patients without residual nidus on the basis of postresection color Doppler and postoperative angiogram, the postresection RI was 0.62 (+/-0.04). In two patients, the postresection scan identified a nidus with persistent low RI flow. Once residual AVM was resected, the RI became significantly higher. A postoperative angiogram confirmed complete resection of the AVM in all patients. Intraoperative duplex Doppler allowed more accurate localization of the AVM nidus. RI of the vessels around the AVM helped to distinguish vessels feeding the AVM from en passant vessels. Furthermore, comparison of pre-resection and postresection RI accurately indicated the completeness of resection.