IMG-53. Relationship and natural history of focal areas of signal intensity (FASI) and non-optic gliomas on MRI in Neurofibromatosis Type 1

AIM To investigate the development and natural history of focal areas of signal intensity (FASI) and non-optic gliomas in a large cohort of neurofibromatosis type 1 (NF1) patients. Background: NF1 is an autosomal dominant disorder that involves multiple organ systems and predisposes individuals to the development of both benign and malignant brain tumors. FASI are histopathologically characterized by spongiform myelinopathy or vacuolar changes within myelin, indicative of aberrant myelination. While typically benign and often regressing, their imaging features can overlap with gliomas, and some gliomas have been observed to develop in regions previously identified as FASI. Gliomas are differentiated from FASI by imaging features such as enhancement, mass effect, and/or enlargement over time. RESULTS Records of 1373 patients with NF1 (aged 2 to 81 years) were reviewed and 679 patients had ≥1 MRI available for review. Of those, 512 (75.4%) had ≥1 FASI and 160 (23.6%) had ≥1 glioma. Those with FASI were more likely to have gliomas (29.5% of those with FASI vs 5.9% without; p<0.001). 370 patients with FASI had follow-up MRI. 46 gliomas were identified from a lesion previously identified as FASI; In these patients, the median age of FASI identification was 7 years and the median age of glioma diagnosis was 13 years, and the brainstem was the most common location, followed by the corpus callosum and cerebellum. 7/46 (15%) were confirmed glioma on biopsy and and 7/46 (15%) required intervention (surgery, chemotherapy, or radiation). CONCLUSION Our data demonstrates that many NF1 patients develop both FASI and gliomas and the presence of FASI is associated with an increased risk of glioma. Many gliomas developed in regions previously identified as FASI, some necessitating treatment. Additional research is needed to elucidate the relationship between FASI and glioma development and inform clinical decision-making regarding MRI monitoring of FASI.