STMO-09 Recovery from speech deficit after injury to frontal aslant tract in glioma surgery

BACKGROUND: The frontal aslant tract (FAT) is a white matter fiber connecting the superior frontal gyrus to the lateral inferior frontal gyrus. Damage to FAT in dominant hemisphere can lead to speech deficits which, in most cases, resolve within weeks to months. However, little is known about mechanisms of recovery and factors for predicting permanent language deficits. METHODS: Eighteen patients with glioma (age ranged 24 to 78, 10 glioblastomas and 8 lower grade gliomas) located in the medial frontal lobe in the dominant hemisphere involving the supplementary motor area (SMA) and FAT were included. FAT was visualized using diffusion tensor imaging tractography in pre- and postoperative MRI. Postoperative language deficit, resected area of FAT and surrounding brain regions including the cingulate gyrus and corpus callosum (CC) were retrospectively reviewed. RESULTS: In 17 of 18 cases, postoperative language deficits were observed. Speech deficits resolved within a month in 12 cases, while recovery was incomplete in five cases. In two patients without complete recovery, CC located beneath SMA was removed because of tumor infiltration. Other two patients had substantial injury of middle third portion of FAT. The last case had preceding infarction in the contralateral frontal white matter including FAT. In cases with complete language recovery, transcallosal fibers connecting the contralateral SMA to the ipsilateral inferior frontal gyrus were detected by postoperative DTI-tractography. These fibers were damaged anywhere along its length in patients without complete language recovery, indicating that they may play an important role in recovery after FAT injury. CONCLUSION: Injury to CC or middle third portion of FAT can cause permanent language disorder. Transcallosal fibers from contralateral SMA seems to be involved in the recovery from language deficit after injury to FAT. In glioma surgery involving dominant SMA or FAT, these fibers should be preserved to avoid permanent speech deficit.