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

backgroundHypoglossal schwannomas (HSs) are rare lesions comprising approximately 1% of intracranial schwannomas. For treatment of these lesions, both microsurgery and radiosurgery are accepted modalities. While post-radiosurgery transient tumor enlargement (TTE) is well described in other intracranial schwannomas, it is not well documented in HSs due to their rarity. The authors present 2 cases of TTE in HS post-radiosurgery that led to clinical deterioration. OBSERVATIONS: Two patients with HS developed brainstem compression secondary to Gamma Knife surgery TTE within 6 months of treatment at the authors' center. Both needed surgical debulking of the intradural portion of the HS to relieve symptoms. LESSONS: 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.