Amanda Holowatyj

BACKGROUND: For small- to medium-sized vestibular schwannomas, especially in patients with preserved hearing and no mass-effect symptoms, Gamma Knife radiosurgery (GKRS) is a preferred initial treatment. It provides effective tumor control and long-term hearing preservation. In the event of a tumor progression, reirradiation remains an option. A rare occurrence is the development of a second schwannoma along the same nerve. In such cases, repeat GKRS can be challenging, as it requires balancing local control with minimizing integral radiation dose and potential toxicity from reirradiation. The authors highlight the feasibility of repeat GKRS and the dosimetric considerations involved in radiating a second schwannoma along the same nerve. OBSERVATIONS: A 35-year-old woman with a history of headaches and a right-sided vestibular schwannoma underwent GKRS as treatment for the tumor. After being under surveillance from 2013 to 2025, the patient’s vestibular schwannoma remained stable. After experiencing a worsening right-sided tinnitus, an updated MRI study revealed a new intracanalicular nodular formation along the nerve, which was treated with GKRS. LESSONS: This case demonstrates the safety and efficacy of GKRS as a retreatment option in the rare occurrence of a second vestibular schwannoma developing along the same cranial nerve. https://thejns.org/doi/10.3171/CASE25667

BACKGROUND: While deep brain stimulation (DBS) is an effective therapy for essential tremor (ET), Gamma Knife radiosurgery (GKRS) offers a noninvasive alternative for patients who are poor surgical candidates or who experience DBS-related complications. Although GKRS ventral intermediate nucleus (VIM) thalamotomy is generally safe, very delayed adverse effects are uncommon and not well characterized. OBSERVATIONS: A 69-year-old woman with medically refractory ET underwent right VIM DBS, but the device was later explanted due to infection. Because she was high-risk for reimplantation, she proceeded with GKRS VIM thalamotomy. Eight years later, she developed progressive left-sided weakness and gait deviation. MRI revealed a new right thalamic cystic lesion precisely colocalized with the prior GKRS target. Stereotactic aspiration demonstrated acellular, proteinaceous fluid without evidence of malignancy or infection, consistent with a delayed postradiosurgical cyst. Neurological function improved following drainage. LESSONS: Delayed cyst formation may occur many years after GKRS VIM thalamotomy and should be recognized as a rare but clinically significant late complication. Given the typical 7- to 10-year latency observed across radiosurgical cystogenesis, long-term but low-frequency MRI surveillance, such as a 1-year posttreatment baseline followed by imaging every 2–3 years or sooner with new neurological symptoms, may facilitate earlier detection and intervention. https://thejns.org/doi/10.3171/CASE25725