SURG-23. Intraoperative ultrasound guided brain shift correction provides dual benefit of accurate resection control and precise functional landmark orientation during surgery for eloquent tumors

BACKGROUND Intra-axial tumor resection is guided by the principle of maximal safe resection. Image guided surgery based on preoperative MR imaging provides useful surgical planning information including functional subcortical substrates which form the limits of resection. However, brainshift can render this inaccurate. Intraoperative ultrasound, on the other hand, is a powerful imaging tool and provides reliable resection control. When integrated with navigation, it enables image-fusion based update in navigation accuracy, thereby restoring its value for real-time guidance. METHODS Illustrative cases are presented to highlight the workflow and clinical value of the technique. Preoperative MR based registration of patient to image space was performed in all cases. Intraoperative ultrasound (BK 5000 and Activ, BK Medical, GE Healthcare), integrated with navigation (Brainlab Kick system with Ultrasound navigation software) was used to acquire serial IOUS scans at various stages of surgery. A rigid image fusion-based algorithm (SNAP to MRI, Brainlab) was applied to correct linear brain shifts at various stages. Realignment of anatomical landmarks and functional substrates (tracts) was recorded and correlated with functional mapping findings. Findings: IOUS reliably depicted tumor, residue and anatomical landmarks in all cases. Brain shift was observed in all cases. It was variable (in direction and severity) and occurred at most stages during the surgical procedure. Correction was successful, allowing recalibration of anatomical and functional landmarks, ensuring accuracy of image guided surgery. Tumor resection control was itself based on the updated IOUS findings. Illustrative case descriptions highlight the benefit of this technique demonstrating the before and after brainshift correction findings. CONCLUSIONS Real-time intraoperative ultrasound-based brain shift correction can restore accuracy of conventional MR-based image guided surgery. It also is a reliable resection control tool, thereby providing dual benefit during intra-axial tumor resections in eloquent areas.