Radiofrequency Thermocoagulation Targeting Propagation Network in MRI-Negative Post-Encephalitic Insular Epilepsy

Overview

This case study demonstrates that radiofrequency thermocoagulation (RFTC) targeting the propagation network (PN) can effectively control seizures in MRI-negative post-encephalitic insular epilepsy. By disconnecting the PN between the insula and perirolandic area, seizure frequency was significantly reduced without resecting the epileptogenic network (EN).

Background

Post-encephalitic epilepsy is frequently drug-resistant and challenging to localize when MRI is negative. The epileptic network consists of the epileptogenic network (EN), responsible for seizure onset, and the propagation network (PN), which facilitates seizure spread. Surgical strategies traditionally focus on EN disruption, but recent advances in stereoelectroencephalography (SEEG) allow detailed network evaluation, enabling alternative approaches such as PN disconnection. This case explores RFTC targeting the PN in a patient with insular epilepsy following encephalitis, with no detectable lesions on MRI or PET.

Data Highlights

Preoperative MRI showed bilateral claustrum hyperintensities at encephalitis onset, which resolved before surgery. SEEG localized seizure onset to the left Heschl’s gyrus and anterior insula, with propagation to the perirolandic area. Epileptogenicity index mapping revealed highest values in the left insular cortex and temporal operculum. Cortical stimulation elicited symptoms matching habitual seizures. RFTC was performed at 44 coagulation lesions (5-mm diameter, 70 °C, 60 s) along nine trajectories targeting subinsular white matter tracts connecting the insula to the perirolandic area.

Key Findings

• Seizures originated in the left Heschl’s gyrus and anterior insula, spreading rapidly to temporal, parietal opercula, and perirolandic areas.
• High epileptogenicity index localized to the left insula and temporal operculum, confirming the epileptogenic network.
• Cortical stimulation of the insula induced neurological symptoms corresponding to habitual seizures, indicating an abnormal hyperexcitable network.
• Direct resection or ablation of the epileptogenic cortex was not feasible due to functional risks and extensive spread.
• RFTC targeted the propagation network by disconnecting subinsular white matter tracts between the insula and perirolandic area, avoiding eloquent cortex and critical pathways.
• Post-RFTC, the patient experienced significant seizure reduction, demonstrating the efficacy of PN disconnection in MRI-negative post-encephalitic epilepsy.

Clinical Implications

This case highlights the utility of SEEG-based network analysis to identify epileptogenic and propagation networks in MRI-negative epilepsy. Targeting the propagation network with RFTC offers a minimally invasive alternative to resection, especially when the epileptogenic cortex is functionally critical or widespread. Careful planning using diffusion tensor imaging tractography can optimize lesion placement to maximize seizure control while preserving neurological function.

Conclusion

RFTC targeting the propagation network can achieve favorable seizure control in drug-resistant, MRI-negative post-encephalitic insular epilepsy. This approach expands surgical options by focusing on network disconnection rather than direct lesion ablation.

References

1. Author/Source/Year -- Epileptogenicity index and network evaluation in epilepsy
2. Author/Source/Year -- Cortical stimulation mapping in epilepsy surgery