Supplementary Material for: Primary Gamma Knife Radiosurgery as a Treatment Option for Hamartoma of Floor of Fourth Ventricle: A case report of Pediatric Hemifacial Spasm

Introduction
Pediatric hemifacial spasm (HFS) is rare, presenting early in infancy, and often fraught with subsequent psychomotor and intellectual deficits. Fourth ventricular hamartoma (FVH) is a rare cause of HFS with only 5 cases reported in literature. While Gamma-knife radiosurgery (GKRS) has been used to treat hypothalamic hamartomas, this is the first case of FVH treated with primary GKRS.

Case Presentation
A two-year-old female presented with persistent episodes of hemifacial spasms and dystonic posturing with an early resistance to medication. Thorough radiological profiling of the fourth ventricular tumor is the suggested tentative diagnosis of FVH. The patient’s guardians refused surgical intervention and gave consent for GKRS aware of the lack of literature on its use in FVH. She underwent frame-based GKRS covering a total target volume of 0.986cc with 13Gy@50% with Leksell Perfexion. The patient showed a phasic response to GKRS with remarkable seizure control at a 1.5-year follow-up.

Conclusion
Previous studies have suggested that gelastic seizures of hypothalamic hamartoma are comparable to hemifacial spasms of FVH. Our case exemplifies another key similarity between the two, i.e., a near-congruent phasic response to GKRS. This hints at the underlying pathophysiology of HFS in similar pathologies and GKRS as a treatment option in select patients.