Rosette-forming glioneuronal tumours: two case reports and a review of the literature

H3 K27M mutation in rosette-forming glioneuronal tumors: a potential diagnostic pitfall

According to the fifth edition of the World Health Organization (WHO) classification of tumors of the central nervous system (CNS), diffuse midline glioma H3 K27-altered is a grade 4 infiltrative glioma that arises from midline anatomical structures and is characterized by the loss of H3 K27me3 and co-occurring H3 K27M mutation or EZHIP overexpression. However, the H3 K27M mutation has also been observed in circumscribed gliomas and glioneuronal tumors arising in midline anatomical structures, which may result in diagnostic pitfalls.Rosette-forming glioneuronal tumor (RGNT) is a CNS WHO grade 1 neoplasm that histologically features neurocytic and glial components and originates in midline anatomical structures.This study aimed to assess whether RGNTs, similar to other midline tumors, may exhibit immunohistochemical loss of H3 K27me3 and harbor the H3 K27M mutation.All seven analyzed RGNTs displayed immunohistochemical loss of H3 K27me3 in all tumor cells or H3 K27me3 mosaic immunostaining. In one case, H3 K27me3 loss was associated with the H3 K27M mutation, whereas the other six cases did not exhibit any H3 mutations or EZHIP overexpression. During a follow-up period of 23 months, the H3 K27M-mutant case remained unchanged in size despite partial resection, indicating that the H3 mutation may not confer higher biological aggressiveness to RGNT.The immunohistochemical loss of H3 K27me3 co-occurring with the H3 K27M mutation may result in the potential misdiagnosis of RGNT, especially in cases of small biopsy specimens consisting of only the glial component.

Imaging of pediatric glioneuronal and neuronal tumors

Glioneuronal tumors (GNTs) are an expanding group of primary CNS neoplasms, commonly affecting children, adolescents and young adults. Most GNTs are relatively indolent, low-grade, WHO grade I lesions. In the pediatric age group, GNTs have their epicenter in the cerebral cortex and present with seizures. Alterations in the mitogen-activated protein kinase (MAPK) pathway, which regulates cell growth, are implicated in tumorigenesis. Imaging not only plays a key role in the characterization and pre-surgical evaluation of GNTs but is also crucial role in follow-up, especially with the increasing use of targeted inhibitors and immunotherapies. In this chapter, we review the clinical and imaging perspectives of common pediatric GNTs.

A Rare Lesion in the Anterior Region of the Third Ventricle: Rosette-Forming Glioneuronal Tumor

Rosette-forming glioneuronal tumor (RGNT) is a rare and indolent mixed glioneuronal tumor involving primarily the fourth ventricular region and occurring predominantly in young adults. We present a case of a 44-year-old woman presented with progressive headaches, vomiting, and a sudden decreasing level of consciousness. The magnetic resonance imaging showed a regular lesion within the anterior portion of the third ventricle and the patient underwent an endoscopic approach to remove the tumor that was exclusively within the anterior portion of the third ventricle. Histopathology showed an RGNT that was totally removed. We also report some unusual complications that are described in the literature and are related to ventricular endoscopy such as seizures and hydroelectrolyte disorders. With two years of follow-up, the patient had no complaints and no tumor progression was observed.