It is important to differentiate radiation necrosis (RN) from tumor recurrence because these conditions require different treatments. Despite the use of various imaging techniques, this distinction remains difficult due to the high heterogeneity of brain tissue. Stereotactic biopsy is still considered the gold standard for a definitive diagnosis of RN despite its invasiveness. However, if the location of the lesion is in the brainstem, stereotactic biopsy is very difficult to even for skillful

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... urgeons. We herein report a case of a 24-year-old male with a history of medulloblastoma at the age of 5, who presented with distinct gait disturbance and dysarthria at a regular visit. The initial radiological diagnosis of a brain mass was recurrent medulloblastoma. Considering the initial diagnosis, additional radiotherapy was considered. Nevertheless, the chance of the mass being RN could not be eliminated. Despite the high risk due to the location of the lesion, a frame-based stereotactic biopsy was performed. The pathological diagnosis after the biopsy confirmed the lesion as RN. This case illustrates the importance of stereotactic biopsy in differentiating between tumor recurrence and RN, even when the location of the lesion makes it challenging.