Résumé
Object. The molecular profile of diffuse WHO Grade II gliomas involving the insular lobe, with a possible impact on outcome, is controversial. The authors undertook this study to investigate a possible difference of molecular patterns between purely insular Grade II gliomas and paralimbic Grade II gliomas that involve both the insular lobe and the frontal and/or temporal structures.
Methods. From a consecutive series of 47 patients who underwent resection of a Grade II glioma invading the insula, 2 subgroups were identified. The first subgroup included 11 patients with a purely insular tumor. The second subgroup included 36 patients with a paralimbic Grade II glioma also involving the frontal and/or temporal lobe. The authors searched systematically for TP53 mutations, 1p19q codeletion, and IDH1/IDH2 mutations.
Results. There was no significant difference between the 2 subgroups with respect to 1p19q codeletion or TP53 mutations rates. Conversely, IDH1/IDH2 mutations were found in all 11(100%) of the insular Grade II gliomas but only 20 (55%) of 36 paralimbic Grade II gliomas (p = 0.008). Ten (28%) of the 36 patients in the paralimbic tumor group experienced a malignant transformation, and 6 of them died; whereas neither transformation nor death occurred in the insular tumor group (trend toward significance, p = 0.088).
Conclusions. These findings demonstrate for the first time distinct IDH1/IDH2 and consequently distinct "triple-negative" patterns in purely insular versus paralimbic Grade II gliomas. Such findings could explain discrepancies reported in the literature, because insular and paralimbic gliomas have not been separated in previous reports: These results may enable physicians to refine the management of Grade II gliomas involving the insula according to the presence or lack of invasion of the frontal and/or temporal areas. (http://thejns.org/doi/abs/10.3171/2012.11.JNS121100)