Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has emerged as a minimally invasive alternative for drug-resistant epilepsy and pediatric brain tumors, particularly in deep-seated lesions where open surgery presents significant risks. However, the multimodal imaging characteristics of lesions during and after MRgLITT remain underexplored. This study aims to describe the MRI features of MRgLITT-treated lesions in pediatric patients both intraoperatively and during long-term follow-up.

We conducted a retrospective analysis of 26 pediatric patients(32 procedures) treated using MRgLITT, including focal cortical dysplasias, low-grade tumors and hamartomas. Imaging acquisition included preoperative, intraoperative, and postoperative MRI with advanced sequences(T1-weighted, FLAIR, DWI, ASL perfusion, and MR spectroscopy). Lesion evolution was assessed over a one-year follow-up period.

Intraoperatively, lesions showed a rim of high signal on DWI and on post-contrast T1-weighted images, a lactate peak on MR spectroscopy, and the majority of them had peripheral high signal on FLAIR associated with a low signal core and increased CBF on ASL. During follow-up, lesions may increase in size in the first days or weeks, then decrease in size mainly in the first 3 months and tend to stabilize at 9 months, with persistent gliotic changes on FLAIR sequences. Contrast enhancement resolved in epilepsy-related lesions, but small areas remained in most tumors without correlation with progression.

MRgLITT results in a predictable pattern of imaging changes, with lesion contraction occurring primarily within the first 3 months. Understanding these radiological markers is essential for optimizing post-procedure management and treatment decisions in pediatric epilepsies and tumors.