T2-FLAIR mismatch sign

The T2-FLAIR mismatch sign describes the MRI appearance considered highly specific for diffuse astrocytoma (IDH-mutant, 1p/19q-non-codeleted molecular status), as opposed to other lower-grade gliomas. It is particularly helpful in distinguishing a diffuse astrocytoma from an oligodendroglioma that will not demonstrate T2-FLAIR mismatch.

Radiographic features


On T2 weighted images, these tumors have extensive areas of fairly homogeneous and strikingly high signal. On T2-FLAIR, instead, the majority of these areas become relatively hypointense in signal due to incomplete suppression. At the margins of the tumor, a rim of hyperintensity is usually seen.  This appearance is typical of the entity previously known as protoplasmic astrocytoma which is, however, no longer recognized as a distinct entity in the current WHO classification of CNS tumors.

Differential diagnosis

It is important to note that similar signal characteristics can be seen in the bright rim sign of DNET, although almost invariably DNETs are smaller .