Early cystic enlargement of hypoglossal schwannoma causing brainstem compression post–Gamma Knife radiosurgery: illustrative cases

TTE is a well-documented reaction of schwannomas to radiosurgery. In the context of HS, the authors believe that the risk of brainstem compression is substantially higher in HS due to the tapered configuration of the posterior fossa, which narrows at the foramen magnum. As the hypoglossal nerve courses just above the foramen magnum, the available space for accommodation of any TTE in that area is very limited, and even a small degree of tumor swelling can cause significant brainstem compression. Upfront radiosurgery should thus be used with caution in HS, especially for lesions already abutting the brainstem. https://thejns.org/doi/10.3171/CASE25933.