gms | German Medical Science

Objective: Insula is a common anatomical site for low-grade gliomas and gliomas in this pose a significant therapeutic challenge due to their deep localization, infiltrative nature and proximity to the MCA branches and projection fibers. Conflicting reports have been published in the last 5 years regarding the molecular characteristics of insular gliomas with some groups correlating the localization with distinct molecular characteristics. This report aims at analyzing radiological, molecular biological findings of insular gliomas and the impact of these parameters on patient outcome.

Method: Only patients who had tumor tissue for molecular analysis were included in the study. The cohort consisted of 27 insular WHO grade-II gliomas, which were operated at one institution by one neurosurgeon and diagnosed by one single neuropathologist. The cohort consisted of 15 astrocytoma, 10 oligodendroglioma and 2 oligoastrocytoma patients. Immunohistochemistry for expression of IDH, Olig-2, Ki67, EGFR, VEGF, pBRAF, c-myc PTEN, p16Ink4A , TP53 protein and MGMT methylation was performed. 1p19q co-deletions were determined by FISH and/or microsatellite analysis. hTERT promoter mutations, IDH mutations were screened with Sanger sequencing or mini-sequencing. The incidences of the molecular genetic changes were compared to other low-grade gliomas of the same histology, which did not involve the insula. Volume, extent, tumor border characteristics, extent of surgical resection, need for adjuvant therapies, recurrence free and overall survival as well malignant degeneration were also documented and correlated with molecular findings.

Results: When compared to frontal, temporal or parietal tumors (n=39), oligodendrogliomas of the insula (n=10) displayed a disproportionally low p16Ink4A protein expression (p<0.05). Other ongogenic findings were comparable. There was no survival difference between insular or frontal-temporal-parietal oligodendrogliomas. Astrocytomas in the insular (n=15), frontal, temporal or parietal lobes (n=16) displayed similar oncogenic changes. There was a tendency towards worse survival outcome in insular astrocytomas when compared to other hemispheric (Frontal-temporal-parietal) astrocytomas.

Conclusions: There is no single molecular marker that is correlated with the clinical behavior of insular gliomas.