A Cohort Analysis of Truly Incidental Low-Grade Gliomas

BACKGROUND: Management of low-grade gliomas (LGGs) is controversial. Incidental LGGs are thought to represent an earlier stage in the disease process compared with symptomatic LGGs. With advanced imaging techniques, the discovery of these lesions is expected to increase, resulting in clinical need for further understanding of these tumors. This study aimed to identify the incidence of incidental LGGs across 2 large European neurosurgical centers and review management and survival of tumors compared with symptomatic cranial LGGs over a 5-year period. METHODS: LGGs managed during 2015-2019 at the Royal Victoria Infirmary and Munster University Hospital were retrospectively reviewed. An incidental finding was strictly defined as one discovered secondary to routine clinical or research imaging, not associated with investigation for a space-occupying lesion, with no associated symptoms. All histomolecular pathology reports were reviewed. RESULTS: Of 150 cases of World Health Organization grade II tumors identified at both centers, 82 were symptomatic, diffuse LGGs, with 20 discovered incidentally. There were 48 nondiffuse and/or pediatric tumors, which were excluded. Incidental LGGs were mostly IDH mutated and oligodendroglial with a trend toward improved overall survival and significantly increased progression-free survival compared with symptomatic LGGs (P = 0.024). In all cases, regardless of presentation, progression-free survival and overall survival were significantly improved following gross total resection versus biopsy (hazard ratio 0.45 [95% confidence interval 0.21-0.95], P = 0.037 vs. hazard ratio 0.10 [95% confidence interval 0.02-0.44], P = 0.003). CONCLUSIONS: In this study, differences in characteristics and survival between incidental and symptomatic LGGs were present, yet not significant owing to the rarity, and therefore small sample size, of incidental LGGs. Further global collaboration and development of an international glioma registry with a focus on symptoms, imaging indications (if incidental), histomolecular data, and management are needed.