Location of incidental and symptomatic LGGs. A review of comparative studies

Incidental low-grade gliomas (iLGG) are frequent in non-eloquent brain regions. We systematically review the literature on iLGG to evaluate the lesion distribution and we further investigated the maximum lesion overlay. A secondary aim was testing the association between histomolecular subtypes and iLGG lesion localization. A search was performed in PubMed, Ovid Embase and Scopus for articles published between January 2000 and March 2025 using terms such as glioma, astrocytoma, oligodendroglioma, incidental, asymptomatic, natural history. Study selection / data extraction were independently performed by two reviewers. A lesion mask subtraction analysis (iLGG vs. symptomatic (sLGG) gliomas) was performed using anatomical regions of interest derived from the patients' lesion sites. Of the 95 articles screened on full-text 22 were included. 1093 gliomas (mean volume 26.0 ± 11.5 cm³) were analyzed. A within-(iLGG) group analysis on the number of lesions per area showed a significant predominance of frontal lobe lesions (p < 0.001), and an equal involvement of the left and right hemisphere (p = 0.470). The most frequent reason for MRI was headache. A between-(iLGG vs. sLGG) group analysis showed an increased proportion of frontal lesions in the iLGGs vs. sLGGs (Z = -2.693, p = 0.006). The MRI subtraction analyses (iLGG vs. sLGG) confirmed a more prevalent frontal location in iLGG vs. sLGG. The number of oligodendroglioma were highly correlated with the number of frontal (p < 0.001) lesions. In the present exploratory study many patients with iLGG have frontal lesions to a greater extent than in sLGG. We discuss the clinical implications of this neuroanatomical pattern.