QUIZ: No. 21, 27/07/2025

NCCT

MRI

ANS – IDH-mutant, 1p/19q non-codeleted diffuse astrocytoma

The T2/FLAIR mismatch sign describes a radiologic pattern in which a solid tumor exhibits very high signal intensity on T2-weighted MRI images but shows incomplete suppression on FLAIR images, typically with a peripheral rim of hyperintensity. This phenomenon is due to the tumor's high water content and low cellularity in central regions, resulting in incomplete nulling of fluid-like signal on FLAIR. The sign is most prominent in non-enhancing lesions with minimal edema and is highly specific  and is a recognized radiogenomic marker and is highly specific for IDH-mutant, 1p/19q non-codeleted astrocytomas.

In this case, the lesion demonstrated this mismatch appearance, suggestive of a diffuse astrocytoma. The patient underwent right frontoparietal craniotomy and tumor excision. Histopathology and immunohistochemistry (IHC) confirmed the diagnosis of IDH-mutant astrocytoma, WHO grade II.

TEACHING POINTS

v T2/FLAIR mismatch sign is a highly specific, though not sensitive, MRI biomarker for IDH-mutant, 1p/19q non-codeleted diffuse astrocytomas.

v This imaging signature can aid in non-invasive molecular classification, guiding diagnosis and therapeutic decisions.