Highly infiltrating oligodendrogliomas show different morphology from typical oligodendrogliomas while maintaining good response to chemo-radiation therapy.

Abstract Oligodendrogliomas are diffuse gliomas located in the cerebral hemisphere, and the MRI typically show swollen cortex and subcortical white matter by the tumor cells. IDH mutation and 1p/19q co-deletion define oligodendrogliomas in WHO classification, and these genetic alterations are associated with good response to chemo-radiation therapy and better prognosis compared to the IDH-mutant astrocytomas. We reviewed MRI findings of 60 oligodendrogliomas with 1p/19q co-deleted tumors which were diagnosed at Dokkyo Medical University since 1999. Of those, 3 cases showed highly infiltrating pattern in which tumors were more predominant in the white matter than the cortex and the infiltration involved multiple lobes. We retrospectively investigated those 3 cases for histological features, treatment, and clinical outcome. There were 2 males and 1 female. MRI showed faint-brushed Gd enhancement around the center of the tumor-infiltrated area in 1 case, while there was no enhancing lesion in other 2 cases. All three underwent stereotactic biopsy. Histologically, all 3 cases lacked typical oligodendroglioma morphology: the tumor cells have irregular round, oval to elongated nuclei without perinuclear halo and had dense, closed chromatin similar to astrocytoma. Two cases underwent chemotherapy (TMZ and PAV accordingly), without radiation and 1 case underwent chemotherapy with radiation as the primary treatment. Interestingly, all three tumors responded well not only to the primary treatments but also to the radiation therapy administered after recurrence, although all eventually succumbed to the tumor. PFS were 16, 37, 67 months and OS were 104, 70, 115 months for each, which were at the worse end as oligodendrogliomas but are apparently better than astrocytomas. Highly infiltrating oligodendrogliomas appeared to show significantly different MRI and histological features from typical oligodendrogliomas that primarily involve cerebral cortex. The underlying mechanism of such differences might involve specific genetic alterations and/or gene expression alterations that may not affect treatment response.