Abstract
BACKGROUND: The diagnosis of intracranial extraosseous Ewing's sarcoma (EES) poses challenges due to the absence of specific clinical and imaging features prior to surgery. It is crucial to differentiate the tumor from other small round cell malignancies postoperatively. OBSERVATIONS: A 7-year-old patient was admitted to the authors' hospital due to the in situ recurrence of a posterior fossa tumor more than 1 month after the initial surgery for headache. Subsequently, a second surgery was performed at the authors' hospital, and pathological analysis indicated medulloblastoma. Genetic testing indicated Ewing's sarcoma. After 16 cycles of chemotherapy and 8 weeks of focal radiotherapy, the patient continued to exhibit clinical and radiographic remission. Whole-spine magnetic resonance imaging (MRI) revealed intraspinal enhancing lesions, which extended throughout the entire spinal canal. Palliative treatment was administered. The patient has been under observation for 2 months thus far, demonstrating disease stability as a result of the palliative treatment. LESSONS: Primary intracranial EES is an exceptionally rare condition that can be easily misdiagnosed. Genetic testing is necessary to differentiate it from other small round cell tumors. Currently, a combination of surgery and chemoradiotherapy has proven to be an effective treatment approach. Postoperative follow-up should include MRI examination of the entire nervous system to detect any cerebrospinal fluid seeding metastasis and reduce mortality. https://thejns.org/doi/10.3171/CASE24488.