45-year-old male with symptomatic mass in the frontal lobe

A 45-year-old male patient developed focal seizures in his right arm. Neuroimaging demonstrated a tumor of the left frontal lobe. Tumor classification was undecided after stereotactic biopsy. Neuropathological examination of the open biopsy specimen revealed overlapping morphological features of an oligodendroglioma and a central neurocytoma. Groups of tumor cell featured the typical "fried egg" appearance seen in oligodendroglioma; microcalcifications and a network of branching non-proliferating vessels were present. Neurocytoma-like features included small nucleus-free areas of neuropil and perivascular pseudorosettes. Neuron specific enolase was strongly expressed cytoplasmically in the tumor cells and the "neuropil islands" were found to express synaptophysin. The final diagnosis of an oligodendroglioma with neurocytic differentiation was based on tumor location, clinicopathological findings and diagnostic genotyping. Combined loss of heterozygosity (LOH) on the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q), the "molecular signature" of oligodendrogliomas, was revealed. Besides supporting the diagnosis of an oligodendroglioma, the molecular data allow for additional therapeutic options. These tumors may point to the presence of yet another potential tumor precursor cell similar to the recently discovered "N-O"-cells in the cerebral cortex of rats, capable of differentiation into neurons and oligodendrocytes.