Bright rim sign (DNET)

The bright rim sign, also known as the hyperintense ring sign, has been described in dysembryoplastic neuroepithelial tumors (DNET). It is described as a well-defined rim of high signal around the DNET on FLAIR sequences. This T2/FLAIR hyperintense ring, whether complete or incomplete, is fairly sensitive and specific for DNET ². On postoperative imaging, this sign may be a helpful clue for residual tumor or tumor recurrence ². 

On pathologic examination, this bright rim sign corresponds to glioneural elements loosely packed at the margin of the tumor ¹.

This sign can, however, be very difficult to distinguish from the T2/FLAIR mismatch sign seen in astrocytomas, IDH-mutant.