Surgical targeting of large hypothalamic hamartomas and seizure-freedom following MR-guided laser interstitial thermal therapy

Background: Large hypothalamic hamartomas (HH) are often associated with difficult-to-treat, refractory seizures. Although magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has emerged as a useful tool to treat these challenging lesions, postoperative outcomes are variable and potentially related to differences in surgical targeting.

Purpose: We sought to identify differences in the anatomic localization of laser ablations that either did or did not result in seizure freedom.

Methods: Four children who underwent MRgLITT for large HH (3 seizure-free and 1 not seizure-free) were included in the analysis. Ablation volumes were segmented, normalized, and overlaid on a high-resolution hypothalamic atlas. For each lesion, the size, spatial extent, and degree of overlap with key hypothalamic nuclei and surrounding brain regions were computed and compared between ablations that did and did not result in seizure freedom.

Results: Ablation masks that resulted in seizure freedom were smaller and located more centrally than the ablation mask that did not. In addition, ablation masks that resulted in seizure freedom overlapped with regions including the paraventricular nucleus, the posterior hypothalamus and the zona incerta, fornix, and mammillothalamic tract, whereas the single non-seizure-free ablation did not.

Conclusion: Differences in the size, position, and anatomical localization of ablation volumes may be a potential contributor to the variability in postoperative outcomes of large HH treated with MRgLITT. A novel, high-resolution MRI atlas of the hypothalamus identifies a number of regions at the interface of large HH that are preferentially disconnected in seizure-free patients. This method of anatomical localization not only serves as a potential clinical tool for surgical targeting but may also provide novel insights into the mechanisms of epileptogenesis in hypothalamic hamartomas.