NFS-19. Atypical Presentation of Gliomas in Adolescents With Neurofibromatosis Type 1 (Nf1): A Case Series

Abstract BACKGROUND Patients with NF1 are at risk for developing gliomas, usually low-grade in childhood but may be high-grade in adults. In children, the most common sites of disease are the optic pathway and brainstem; tumors in these regions often arise in young children and display histological features characteristic of pilocytic astrocytoma (PA) when biopsied. Typical MRI findings include T2 hyperintense, T1 hypointense lesions with minimal contrast enhancement and no diffusion restriction. Due to the well-established pattern of low-grade tumor formation in children with NF1, as well as the surgically challenging areas in which these tumors develop, low-grade glioma (LGG) therapy is often initiated without histologic confirmation of the diagnosis in classic cases. In cases with atypical disease location, older age at presentation or imaging appearance, a biopsy may be considered to exclude higher-grade lesions. METHODS Retrospective chart review, case series RESULTS Four adolescent patients with NF1 presented with atypical suspected gliomas. All four patients underwent surgical biopsy/resection. Case 1 was a left temporal lesion in the previous radiation field for optic pathway glioma; biopsy confirmed LGG with MAP2K1 mutation and increased focal proliferation index (28%), but methylation did not match with any established classification. The patient progressed through multiple rounds of therapy and succumbed to her tumor. Case 2 was a left occipital lesion; biopsy confirmed PA with CDKN2A deletion. The tumor displayed rapid regrowth, but subsequently stabilized. Case 3 was a right frontal lesion; confirmed PA. The tumor demonstrated some regrowth but then stabilized. Case 4 was a basal ganglia lesion; confirmed PA. The patient has demonstrated stable MRI findings and has not required further intervention. CONCLUSIONS Biopsy yielded helpful prognostic information (additional mutations, proliferation rate) in half of these atypical cases. Biopsy should be carefully considered for NF1 patients with atypical presentation or a history of radiation.