Natural History and Growth Patterns of Incidentally Discovered Diffusely Infiltrating Low-Grade Gliomas: A Volumetric Study

Background: Incidentally discovered diffusely infiltrating low-grade gliomas (iDLGGs) are rare findings on neuroimaging that pose a challenge to neurosurgeons. There is a paucity of data regarding the natural history of these lesions, and thus management is controversial. We characterize the growth rates and patterns of iDLGGs in a cohort of patients who underwent serial magnetic resonance imaging before surgical treatment. Methods: We performed a retrospective review of all adult patients (≥18 years old) with diffuse low-grade glioma diagnosed at our institution between April 2004 and April 2016. iDLGG was defined as any lesion discovered on computed tomography or magnetic resonance imaging performed for reasons and/or symptoms not attributable to the lesion and confirmed on histopathology as low-grade glioma. Tumor growth rates and patterns of growth were analyzed in patients who had serial imaging available. Results: Inclusion criteria were met by 15 patients. Mean velocity of diametric expansion was 2.93 mm/year. Of 15 patients, 11 (73.3%) had tumors with an exponential growth pattern, and 4 (26.7%) had a linear growth pattern. Initial tumor volume was positively correlated (r = 0.78) with velocity of diametric expansion. Conclusions: iDLGGs grow over time, and most exhibit an exponential pattern of growth. Tumor volume at the time of diagnosis is predictive of a faster growth rate, but not the pattern of growth.