Abstracts

Brain tumors responsible for long standing partial epilepsy are characterized by a high prevalence of dysembryoplastic neuroepithelial tumor (DNT), which natural evolution is much more benign than that of gliomas. The pre-operative diagnosis of DNT, which is not yet feasible based on available clinical and imaging data, would help optimizing the therapeutic strategy in this type of tumor. In this study, we have tested whether [¹¹C]-Methionine Positron Emission Tomography (MET-PET) could distinguish DNTs from other epileptogenic brain tumors MET-PET examination was performed in 27 patients with a partial epilepsy of at least six months duration related to a non rapidly progressing brain tumor on MRI. Pathological data were 11 DNTs (41%), 5 gangliogliomas (18%) and 11 gliomas (41%) including 7 low grade (1 pilocytic astrocytoma, 1 pleomorphic xanthoastrocytoma, 3 oligodendrogliomas grade II, 2 oligoastrocytomas grade II) and 4 high grade gliomas (1 astrocytoma grade III, 3 oligodendrogliomas grade III). Visual comparison of methionine uptake between DNT, Gangliogliomas and Gliomas were performed using a chi-2 test. In 25 patients, we also calculated the ratios between 5 mm diameter ROIs placed on the tumor portion dysplaying the highest [¹¹C]-Methionine uptake activity and the controlateral homotopic cortical region (Max AR = Maximal Asymetry Ratio) or the controlateral occipital cortex (OR = Occipital Ratio). Statistical analysis of these semi-quantitative data used a one factor ANOVA. MET-PET visual findings significantly differ between the various tumor types (p[lt]0.0002), regardless of gadolinium enhancement on MRI, and were confirmed by semi-quantitative analysis (p[lt] 0.001 for all calculated ratios). Visually, all gliomas and gangliogliomas were associated with moderate or marked increased tumor methionine uptake, whereas 63% of DNT had a normal methionine uptake, including 100% of those located in the mesio-temporal structures (n = 6). No DNT presented with a marked MET-PET abnormality. On semi-quantitative analysis, post-hoc tests showed that DNTs methionine uptake remained significantly different than gangliogliomas (Max AR: p [lt] 0.005) and gliomas, even after excluding the four high grade gliomas (Max AR: p [lt] 0.0001; OR: p [lt] 0.0001). A normal MET-PET in patient with an epileptogenic and non-rapidly progressing brain tumor is highly suggestive of DNT, whereas a marked increased tumor methionine uptake makes this diagnosis very unlikely. MET-PET appears to be clinically useful in the management of epileptogenic brain tumors.