Mesenchymal tumors of the central nervous system: illustrative case.

backgroundFET-CREB (EWSR1-ATF1) fusion-positive intracranial mesenchymal tumors (IMTs) are locally aggressive with a high recurrence rate, particularly for pediatric patients. Management is challenging because of their complex diagnostic criteria, tumor location, and limited evidence of effective adjuvant therapy. The authors present the case of a child with multiple recurrences of FET-CREB fusion-positive IMT. OBSERVATIONS: A 6-year-old male with cerebral palsy presented with 3 weeks of vomiting, gait decline, and headaches. Physical examination revealed right-sided weakness, facial asymmetry, and dysphagia. Imaging revealed a large right-sided cystic cerebellar mass extending to the cerebellopontine angle, with mass effect on the brainstem and obstructive hydrocephalus. He underwent multiple resections for recurrent disease via a right retrosigmoid craniotomy/craniectomy. Histopathological and molecular testing confirmed an FET-CREB fusion-positive IMT. Efforts toward gross-total resection were limited by the tumor abutting cranial nerves (CNs) VII and VIII. Small residual tumor was intentionally left to avoid neurological decline. Given subtotal resection, adjuvant therapy was initiated. The patient required multidisciplinary rehabilitation and ongoing management for right-sided facial droop and CN VII palsy. LESSONS: This case highlights local aggression of FET-CREB fusion-positive IMTs and the resection preservation trade-off. Molecular confirmation, multimodal care, and novel effective adjuvant therapy are essential. https://thejns.org/doi/10.3171/CASE26367.