T2-FLAIR mismatch in isocitrate dehydrogenase mutant astrocytomas

Objective

To assess the predictive value of T2 appearance as a defining criterion of T2–fluid-attenuated inversion recovery (FLAIR) mismatch sign (T2FM), further characterize tumors that display the marker, and describe its radiographic evolution.

Methods

Records from 64 patients with astrocytomas were assessed for age at diagnosis, sex, tumor characteristics on pretreatment CT, MRI, and pathology, documentation of T2FM, treatment course, and temporal changes in tumor appearance. Cases were divided into those meeting classic criteria (homogenous T2, hyperintense FLAIR rim), those considered geographic (heterogeneous T2, hyperintense FLAIR rim), and those that were negative (no FLAIR rim). Groups were compared using χ², estimate of effect, and qualitative analyses.

Results

Including geographic tumors increased T2FM sensitivity 30% among astrocytomas without decreased specificity for IDH mutation. Tumors with T2FM characteristics were more cystic, less enhancing, and affected younger patients. T2FM persisted in residual tumors following subtotal resection and disappeared with radiotherapy, persisted in 5/8 recurrent tumors that were originally T2FM-positive, and was identified in tumors with high-grade characteristics. T2FM was able to predict IDH mutation status on sequencing when antibody testing was negative.

Conclusions

The presence of a hyperintense FLAIR rim, regardless of T2 appearance, is a reliable indicator of IDH mutation among astrocytomas. Tumors with a FLAIR rim are more cystic and this may lend to their characteristic appearance on MRI. T2FM demonstrates distinctive temporal radiographic changes, may be seen in high-grade gliomas, and may be used in combination with other variables to strengthen prediction of IDH status.