Significance of the electrophysiological border between hypothalamic hamartomas and hypothalamus for the target of ablation surgery

Hypothalamic hamartomas are usually associated with intellectual/behavioral problems and intellectual/behavioral problems. They cause drug-resistant epilepsy that is characterized by unique seizure semiology such as gelastic seizure. Hypothalamic hamartomas have been known to have inherent epileptogenicity and to eliminate the seizures, direct surgical treatment is needed. For the treatment of hypothalamic hamartomas, the surgical disconnection of the hypothalamic hamartomas from the hypothalamus instead of a complete removal has been suggested. However, several surgical treatment methods have not been successful in achieving good seizure outcomes. These unsuccessful outcomes have been attributed to the difficulty in obtaining a complete disconnection due to the absence of clear-cut borders between the hypothalamus and hypothalamic hamartoma as well as the location of hypothalamic hamartomas in deep regions surrounded by critical structures. However, the emergence of stereotactic ablation surgery using laser interstitial thermal therapy or radiofrequency thermocoagulation has shown outstanding seizure outcome with minimal complications making it the first line of treatment for hypothalamic hamartomas

In this study, Dr. Hiroshi Shirozu and Dr. Hiroshi Masuda from Nishiniigata Chuo Hospital in Japan in collaboration with Dr. Shigeki Kameyama from Niigata Seiro Hospital. They sought to confirm the electrophysiological activity of hypothalamic hamartomas by comparison with MRI-based targets and the electrophysiological border between the hypothalamus and hypothalamic hamartoma. Their findings show that through the use of intraoperative semimicrorecording, the electrophysiological features of hypothalamus hamartoma were identified and the electrophysiological border between the hypothalamus and hypothalamic hamartoma was verified. The original research article is published in the Journal Epilepsia.

The research team confirmed the electrophysiological border between the hypothalamus and hypothalamic hamartoma in 73 patients (91.3%). Area potential increases were observed in 31 patients (38.8%) and 56 patients (70.0%) had spike discharges. At each spot, except between area potential increases and spike discharges, different area potentials were seen with the use of semimicrorecording. The hypothalamus had the highest area potential while the area potential decline showed the lowest area potential.

There were 40 patients with mixed-type hypothalamus hamartomas with bilateral attachment, 15 (37.5%) of whom had recording with the trajectory involving the contralateral attachment. Of these 15, five patients (12.5%) displayed the reappearance of spike discharges or restoration of area potential. It was observed that area potential increases or electrophysiological border detection was often associated with freedom from gelastic seizure, although there was no significant difference. The team also noticed that for freedom from gelastic seizure, the detection of spike discharges was not superior to non-detection of spike discharges.

Through this new study, the authors have been able to identify the electrophysiological differences between various structures including hypothalamic hamartoma and adjacent structures related to stereotactic radiofrequency thermocoagulation through semimicrorecording. They also demonstrated successfully that the electrophysiological border at which there was a dramatic decline in area potential between the hypothalamus and hypothalamic hamartoma corresponded with the morphological border MRI. Furthermore, the distribution of the electrophysiologically active area of hypothalamus hamartoma was shown to be in the area close to the border between the hypothalamus and hypothalamic hamartoma. These new findings provide further support for the rationale behind ablation surgery for hypothalamic hamartoma, which is to carry out disconnection at the exact border between the hypothalamus and hypothalamic hamartoma. Further studies have been recommended to investigate the effectiveness of this disconnection method that is limited to precisely the border between the hypothalamus and hypothalamic hamartoma.