Rosette-forming glioneuronal tumor of the septum pellucidum with extension to the supratentorial ventricles: rare case with genetic analysis.

In the original description, rosette-forming glioneuronal tumors (RGNTs) were restricted to the fourth ventricle and/or posterior fossa. Here, we first report an unusual case of RGNT centered in the septum pellucidum and associated with multiple masses occupying the wall of the bilateral lateral ventricles and the third ventricle. No mass was found in the fourth ventricle. Histological and immunohistochemical examination revealed that the tumor presented biphasic differentiation characterized by predominantly neurocytic rosettes and pilocytic astrocytoma-like components with obvious microvascular proliferation. Chromosome 1p/19q deletions and isocitrate dehydrogenase 1 and 2 (IDH1/2) mutations were not identified. Because this case exhibited a worrisome growth pattern, further studies and long-term follow-up are needed to determine the true nature of these tumors.