gms | German Medical Science

Objective: For neurosurgery of patients with lesions around the pyramidal tract, it is most desirable to prevent postoperative complications such as motor paralysis. Brain mapping is of help in identifying motor function. To visualize the course of the fiber bundles, diffusion-weighted (DW) imaging and diffusion tensor imaging using MRI are in use. However, brain shift occurs during surgery. The purpose of this study is to protect motor function during the neurosurgical procedure. We have presented a navigation system based on DW images using intraoperative MRI to depict fiber bundles with the pyramidal tract. In this paper we demonstrate the fiber bundle shift including the pyramidal tract during neurosurgery by the proposed method. DW images were validated using subcortical mapping.

Methods: Patients with lesions around the pyramidal tract, who underwent craniotomy procedure from September 2003 to October 2005 ,were enrolled. Intraoperative imaging was performed after craniotomy and tumor resection using the MRI scanner (0.3T AIRIS2, Hitachi Medical Co.) installed in our operating room. A dedicated integrated head-holder/MR receiver coil (Mizuho Ikakogyo Co.) was used for imaging. DW images (motion probing gradient: anterior to posterior direction; b value: 700 sec/mm²) to depict fiber bundles, T1- and T2- weighted images for anatomical information were obtained. These images were transferred to the navigation system and displayed on a screen. The position of the surgical tool or stimulation electrode probe was tracked by an optical camera. The fiber bundle shift including the pyramidal tract was evaluated by a DW image before and after tumor removal. For preserving brain function, direct electrical stimulation was performed as well to validate the fiber bundle on the DW image.

Results: DW images after craniotomy depicted that the fiber bundles including the pyramidal tract were pressed by the tumor. After tumor resection, it was observed that the bundles were displaced to the regular position in several patients. The bundle shift was not marked in some patients. Subcortical mapping around the fiber bundles on DW images resulted in preserving the motor function in patients.

Conclusions: For neurosurgery of patients with lesions around the pyramidal tract, intraoperative imaging was needed because of the fiber bundle shift. The integrated surgical navigation based on diffusion-weighted imaging with subcortical mapping was useful for performing neurosurgery thereby preventing injury to motor function.