Diffusely invasive supratentorial rosette-forming glioneuronal tumor: illustrative case

BACKGROUND

Rosette-forming glioneuronal tumors (RGNTs) are rare tumors composed of mixed glial and neurocytic components. Most lesions are confined to the posterior fossa, especially in the region of the fourth ventricle, in young adults. In few instances, diffuse involvement of the supratentorial region is identified, thereby creating significant challenges in diagnosis, surgical intervention, and prognostication.

OBSERVATIONS

The authors present a 23-year-old female with chronic headaches, papilledema, and hydrocephalus who underwent radiographic evaluation revealing obstructive hydrocephalus and diffuse supratentorial enhancing and nonenhancing cystic and nodular lesions. The patient underwent a right frontal craniotomy and septostomy. An exophytic nonenhancing right frontal horn lesion was resected, and an enhancing third-ventricular lesion was biopsied. Final pathology of both of the lesions sampled was consistent with RGNT. Next-generation sequencing demonstrated tumor alterations in the FGFR-1 and PIK3CA genes. Targeted therapy with the FGFR inhibitor erdafitinib demonstrated a partial remission.

LESSONS

Diffuse supratentorial spread of RGNT is an extremely rare presentation of an already uncommon pathology. In some cases, gross-total resection may not be feasible. Goals of surgery include acquiring tissue for diagnosis, maximizing safe resection, and treating any associated hydrocephalus. FGFR inhibitors may be of benefit in cases of disease progression.

Rosette-forming glioneuronal tumours are midline, FGFR1-mutated tumours

Rosette-forming glioneuronal tumour (RGNT) is a rare CNS WHO grade 1 brain neoplasm. According to WHO 2021, essential diagnostic criteria are a "biphasic histomorphology with neurocytic and a glial component, and uniform neurocytes forming rosettes and/or perivascular pseudorosettes associated with synaptophysin expression" and/or DNA methylation profile of RGNT whereas "FGFR1 mutation with co-occurring PIK3CA and/or NF1 mutation" are desirable criteria.

MATERIAL AND METHODS

We report a series of 46 cases fulfilling the essential pathological diagnostic criteria for RGNT. FGFR1 and PIK3CA hotspot mutations were searched for by multiplex digital PCR in all cases whereas DNA methylation profiling and/or PIK3R1 and NF1 alterations were analysed in a subset of cases.

RESULTS

Three groups were observed. The first one included 21 intracranial midline tumours demonstrating FGFR1 mutation associated with PIK3CA or PIK3R1 (n=19) or NF1 (n=1) or PIK3CA and NF1 (n=1) mutation. By DNA methylation profiling, 8 cases were classified as RGNT (they demonstrated FGFR1 and PIK3CA or PIK3R1 mutations). Group 2 comprised 11 cases associated with one single FGFR1 mutation. Group 3 included 6 cases classified as LGG other than RGNT (1/6 showed FGFR1 mutation and one a FGFR1 and NF1 mutation) and 8 cases without FGFR1 mutation. Groups 2 and 3 were enriched in lateral and spinal cases.

CONCLUSIONS

We suggest adding FGFR1 mutation and intracranial midline location as essential diagnostic criteria. When DNA methylation profiling is not available, a RGNT diagnosis remains certain in cases demonstrating characteristic pathological features and FGFR1 mutation associated with either PIK3CA or PIK3R1 mutation.

Rosette-forming glioneuronal tumors share a distinct DNA methylation profile and mutations in FGFR1, with recurrent co-mutation of PIK3CA and NF1

Rosette-forming glioneuronal tumor (RGNT) is a rare brain neoplasm that primarily affects young adults. Although alterations affecting the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signaling pathway have been associated with this low-grade entity, comprehensive molecular investigations of RGNT in larger series have not been performed to date, and an integrated view of their genetic and epigenetic profiles is still lacking. Here we describe a genome-wide DNA methylation and targeted sequencing-based characterization of a molecularly distinct class of tumors (n = 30), initially identified through genome-wide DNA methylation screening among a cohort of > 30,000 tumors, of which most were diagnosed histologically as RGNT. FGFR1 hotspot mutations were observed in all tumors analyzed, with co-occurrence of PIK3CA mutations in about two-thirds of the cases (63%). Additional loss-of-function mutations in the tumor suppressor gene NF1 were detected in a subset of cases (33%). Notably, in contrast to most other low-grade gliomas, these tumors often displayed co-occurrence of two or even all three of these mutations. Our data highlight that molecularly defined RGNTs are characterized by highly recurrent combined genetic alterations affecting both MAPK and PI3K signaling pathways. Thus, these two pathways appear to synergistically interact in the formation of RGNT, and offer potential therapeutic targets for this disease.

Malignant Transformation of a Rosette-Forming Glioneuronal Tumor with IDH1 Mutation: A Case Report and Literature Review

Background

Rosette-forming glioneuronal tumor (World Health Organization grade I) is considered as a benign tumor with very low potential for progression. The potential for malignant transformation of this tumor is not known and has never been reported before in literature.

Case Description

We report a 42-year-old man, diagnosed with rosette-forming glioneuronal tumor of the fourth ventricle with a positive isocitrate dehydrogenase 1 mutation, progressed to glioblastoma after 6 years from diagnosis. We discuss the clinical history, radiological findings, and histopathological characteristic with immunohistochemistry findings observed in this unique case.

Conclusions

Despite being acceptable as benign, based on our observations in this case, there is a potential for malignant transformation of rosette-forming glioneuronal tumor. The role of isocitrate dehydrogenase 1 mutation leading to malignant transformation could not be established as our finding is novel and further prospective studies are required to prove this association.

Rosette-forming glioneuronal tumor in the pineal gland and the third ventricle: a case with radiological and clinical implications

A 39-year-old man presented with more than 20 years history of episodic headache and one year history of dizziness, impaired vision and memory disorders. Computed tomography and Magnetic resonance imaging revealed a cystic mass involving the pineal gland, tectum and the third ventricle and obstruction of the aqueduct. Interestingly, the fourth ventricle was not involved in this case. The pathological diagnosis was rosette forming glioneuronal tumor (RGNT). These lesions are considered low-grade tumors (WHO grade I). We describe here the fifth reported patient with a pineal gland RGNT and the eighth reported patient with a RGNT outside the fourth ventricle.