Radiotherapy for Recurrent Intracranial Epidermoid Cysts: A Case Report With 3-Year Follow-Up.

Intracranial epidermoid cysts have high recurrence rates after surgical resection, and alternative strategies are needed when additional surgery is not feasible. We report a 46-year-old woman with a right cerebellopontine angle epidermoid cyst that recurred three times after surgical resections in 2010, 2016, and 2019, complicated by hydrocephalus requiring ventriculoperitoneal shunt placement. At the third recurrence in 2023, the patient refused further surgery, and radiotherapy (RT) to 50.4 Gy in 28 fractions was delivered using a Novalis Tx linear accelerator. During RT, partial neurological improvement was observed. However, approximately one month after RT completion, neurological deterioration occurred, likely attributable to radiation-induced peritumoral edema and tumor swelling, which persisted for approximately two years. Beginning at 2 years post-RT, progressive neurological improvement was observed with radiographic tumor regression. At 3-year post-RT follow-up, the patient continues to improve, with no evidence of malignant transformation. This case uniquely demonstrates the therapeutic effect of standalone RT without concurrent surgical debulking, characterized by a delayed response pattern of transient post-RT worsening followed by gradual improvement.