T2-FLAIR Mismatch: An Imaging Biomarker for Children’s<i>MYB/MYBL1</i>–Altered Diffuse Astrocytoma or Angiocentric Glioma

Abstract

<h3>BACKGROUND AND PURPOSE:</h3> T2-FLAIR mismatch is a highly specific imaging biomarker of <i>IDH</i>-mutant diffuse astrocytoma in adults. It has however also been described in <i>MYB/MYBL1</i>–altered low grade tumors. Our aim was to assess the diagnostic power of the T2-FLAIR mismatch in <i>IDH</i>-mutant astrocytoma and <i>MYB/MYBL1</i>–altered low-grade tumors in children and correlate this mismatch with histology. <h3>MATERIALS AND METHODS:</h3> We evaluated MR imaging examinations of all pediatric patients, performed at the Princess Máxima Center for Pediatric Oncology and the University Medical Center Utrecht between January 2012 and January 2023, with the histomolecular diagnosis of <i>IDH</i>-mutant astrocytoma, diffuse astrocytoma <i>MYB/MYBL1</i>–altered, or angiocentric glioma, and the presence of T2-FLAIR mismatch was assessed. Histologically, the presence of microcysts in the tumor (a phenomenon suggested to be correlated with T2-FLAIR mismatch in <i>IDH</i>-mutant astrocytomas in adults) was evaluated. <h3>RESULTS:</h3> Nineteen pediatric patients were diagnosed with either <i>IDH</i>-mutant astrocytoma (<i>n</i> = 8) or <i>MYB/MYBL1</i>–altered tumor (<i>n</i> = 11: diffuse astrocytoma<i>, MYB-</i> or <i>MYBL1</i>-altered <i>n</i> = 8; or angiocentric glioma <i>n</i> = 3). T2-FLAIR mismatch was present in 11 patients, 3 (38%) in the <i>IDH</i>-mutant group and 8 (73%) in the <i>MYB/MYBL1</i> group. No correlation was found between T2-FLAIR mismatch and the presence of microcysts or an enlarged intercellular space in either <i>IDH</i>-mutant astrocytoma (<i>P </i>= .38 and <i>P </i>= .56, respectively) or <i>MYB/MYBL1</i>–altered tumors (<i>P </i>= .36 and <i>P </i>= .90, respectively). <h3>CONCLUSIONS:</h3> In our pediatric population, T2-FLAIR mismatch was more often found in <i>MYB/MYBL1</i>–altered tumors than in <i>IDH</i>-mutant astrocytomas. In contrast to what has been reported for <i>IDH</i>-mutant astrocytomas in adults, no correlation was found with microcystic changes in the tumor tissue. This finding challenges the hypothesis that such microcystic changes and/or enlarged intercellular spaces in the tissue of these tumors are an important part of explaining the occurrence of the T2-FLAIR mismatch.