The Frequency of Focal Cortical Dysplasia-Like Histologic Features Near Adult-Type Diffuse Gliomas

While the coexistence of focal cortical dysplasia (FCD) and grade 1 noninfiltrative gliomas has been described, to date, only rare case reports have described FCD adjacent to infiltrating gliomas. We therefore sought to determine how often FCD-like findings occur near adult-type diffuse gliomas. This was a retrospective survey of 186 consecutive, newly diagnosed, en bloc glioma resections. Fifty-nine (31.7%) had sufficient adjacent cortex to evaluate for FCD-like features. Among IDH mutant ("IDHmut") gliomas, 40/77 (52%) had adjacent evaluable cortex, whereas only 19/109 (17%) of IDH wild-type ("IDHwt") gliomas did (p < 0.0001). Among cases with evaluable cortex, 15 (25.4%) contained features suggestive of FCD, including radial/tangential dyslamination and/or maloriented neurons. In a multivariable analysis, increasing glioma grade (OR = 4.0, 95% CI = 1.2-13.5, p = 0.027) and IDHmut (OR = 6.5, 95% CI = 1.3-32.2, p = 0.022) emerged as independently positive correlates with the appearance of FCD-like findings. However, FCD-like features were also found in 13/32 (40.6%) cortical samples from adult brains without any neoplastic disease or seizure histories (p = 0.16). Together, these data suggest that, while FCD-like histologic features can be incidentally found in at least a subset of diffusely infiltrative gliomas, the frequencies are not significantly different from that seen in otherwise non-neoplastic brains, and are therefore most likely nonpathologic.