Thin isotropic FLAIR MR images at 1.5T increase the yield of focal cortical dysplasia transmantle sign detection in frontal lobe epilepsy

- Thin-slice (1.0 mm) isotropic FLAIR MR sequences increase the FCD II transmantle sign detection yield by almost 57% in FLE patients at 1.5T.
- Transmantle sign dimensions can vary as little as 3.0-5.0 mm.
- Structural MR protocols that include thin-slice FLAIR sequences can reduce false-negative reports in FLE.

ObjectiveThe transmantle sign is a distinctive imaging marker of focal cortical dysplasia (FCD) type II in frontal lobe epilepsy (FLE), which is revealed predominantly by fluid-attenuation inversion recovery (FLAIR) sequences. Although the transmantle sign detection yield is high by routine imaging protocols for epilepsy at 3T, most centers around the world have access to 1.5T MR technology and FLE patients often receive negative imaging reports. This study investigates the optimization of transmantle detection yield at 1.5T by introducing a 3D thin-slice isotropic FLAIR sequence in the epilepsy imaging protocol.MethodsTwenty FLE patients underwent diagnostic imaging for epilepsy with typical 2D thick-slice (3.0 mm) coronal FLAIR sequences and a 3D thin-slice (1.0 mm) isotropic FLAIR sequences at 1.5T, and transmantle sign detection yields and thickness measurements were derived.ResultsThe 2D thick-slice FLAIR detected a transmantle sign in seven (35.0%) patients. The 3D isotropic thin-slice FLAIR detected a transmantle sign in eleven (55.0%) patients, thereby increasing the transmantle sign detection yield by 57.4%. The mean transmantle sign thickness by thick images was 12.3 mm, by thin images was 8.9 mm, and in the patients undetected by thick FLAIR was 3.5 mm.SignificanceThis study showed that the extratemporal transmantle sign in FLE patients can be thin enough to be missed by thick-slice FLAIR sequences at 1.5T. By introducing 3D thin-slice isotropic FLAIR, false-negative reports can be reduced without reference for higher MR field structural scanning or other modalities, and more FLE patients can benefit from epilepsy surgery candidacy.