Collision tumor: Multinodular and vacuolating neuronal tumor with isocitrate dehydrogenase-mutant diffuse astrocytoma

Herein, we report a case of a collision tumor involving a multinodular and vacuolating neuronal tumor (MVNT) and a diffuse astrocytoma. A collision tumor between these two entities has not previously been reported. The patient is a 35-year-old woman who presented with new-onset hearing loss and ringing in her right ear. Magnetic resonance imaging identified a non-enhancing mass involving the gray matter and subcortical white matter of the left middle frontal gyrus. Additionally, tiny clustered nodules were noted along the underlying subcortical ribbon and superficial subcortical white matter of the left superior frontal gyrus. The patient underwent a left frontal craniotomy and complete resection of the mass. Histologic examination of the resected specimen demonstrated a collision tumor consisting of a diffuse astrocytoma (isocitrate dehydrogenase [IDH] mutant, central nervous system [CNS] World Health Organization [WHO] grade 2) and an MVNT, with the latter demonstrating characteristic morphologic and immunohistochemical features.

Localized overexpression of alpha-internexin within nodules in multinodular and vacuolating neuronal tumors

Multinodular and vacuolating neuronal tumors (MVNT) have been recently referred to as a distinctive neuronal tumor entity based on histopathological findings. They are characterized by multiple tumor nodules, vacuolar alteration and widespread immunolabeling for human neuronal protein HuC/HuD. Only 13 cases have been reported in the literature to date and little is known about the histopathology of these tumors. Herein, we report a case of MVNT with additional confirmation of immunohistochemical features. A 22-year-old woman presented with a continuous headache. MRI showed a subcortical white matter lesion with multiple satellite nodules in the frontal lobe appearing as T2/fluid-attenuated inversion recovery (FLAIR) hyperintensities. Histological examination of the resected lesion revealed well-defined multiple nodules composed of predominant vacuolating tumor cells. The tumor cells exhibited consistent immunolabeling for doublecortin, as well as HuC/HuD, both representative neuronal biomarkers associated with earlier stages of neuronal development. Immunopositivity for oligodendrocyte transcription factor 2 (Olig2) and S100 was also detected in tumor cells. Additionally, significant overexpression of alpha-internexin was observed in the background neuropil limited to tumor nodules. Neuronal nuclear antigen (NeuN), synaptophysin and neurofilament, markers for mature neurons, were either negative or weakly positive. The expression profile of neuronal biomarkers can be distinguished from that of classic neuronal tumors and is the immunohistochemical hallmark of MVNT. In summary, we identified the characteristic tumoral expression of HuC/HuD and doublecortin and the presence of abundant neuropil localized in MVNT tumor nodules, which exhibited widespread alpha-internexin expression. These results supported the presumption that MVNT is a distinct histopathological entity.