Abstracts

Most healthy people have left hemispheric language dominance. Atypical language lateralization may occur naturally, but is more frequent in epilepsy patients. Atypical language may be induced by an early disturbance of the left hemisphere. Dysembryoblastic neuroepithelial tumours (DNET) and ganglioglioma (GG) are developmental tumors, and are an important cause of refractory partial epilepsies. They tend to occur in the temporal lobe. Here, we aim to assess language activation in patients with temporal lobe DNET or GG. We recruited 14 patients (9 DNET, 4 GG, 1 DNET+GG). They all had histological or MRI diagnosis of the tumour. MR imaging was performed on a 3-tesla GE scanner. Functional MRI (fMRI) was performed using a whole brain (22 slides) gradient echo-planar imaging (EPI) technique. The task was a natural language task, where a noun was presented and a corresponding verb had to be generated (Noun-Verb Generation task, NV). Laterality indices (LI) of activated voxels in language related areas were calculated using the formula (Left-Right)/(Left+Right). Left-sided lateralization was diagnosed if the LI was greater than 0.2, atypical lateralization if LI was smaller than 0.2. The analysis was done with SPM99 and iBrain[reg]. Three subjects were left-handed and 11 subjects were right-handed. Two right-handed patients had a right-hemispheric tumor. The tumor was in language related areas in three subjects, and in other temporal lobe regions, not typically involved in language functions, in the remaining 11 patients.
Atypical language was found in thee patients; one had a right-sided tumor (LI 0.04), one had a left posterior middle temporal gyrus (LI -0.4) and one a left insular tumor (LI -0.0). Left-lateralized language was found in the remaining 11 patients, including two patients with a tumor in the superior temporal gyrus (LI 0.4; and 0.7). The two left-handed subjects both had clearly left-lateralized language. The average LI (0.3[plusmn]0.3) was not different from our control group (LI 0.5 [plusmn]0.5, p=0.187). These results indicate that a developmental tumour in the left temporal lobe does not generally induce atypical language lateralization. This may suggest that an early developmental tumor is not interfering with language organization.