An extremely rare case of primary alveolar rhabdomyosarcoma in the central nervous system.

Background: Alveolar rhabdomyosarcoma (ARMS) shows a predilection for the peripheral extremities and is very rarely identified as a primary in the brain. Here, we report a case of ARMS with multiple lesions exclusively within the central nervous system (CNS). Case Description: A 20-year-old man presented to our hospital with a gradually increasing headache and disturbance of consciousness. Neuroimaging showed hydrocephalus and multiple tumor lesions, including in the brainstem and cerebellum, with uniform gadolinium enhancement on T1-weighted magnetic resonance imaging, as well as spinal cord seeding. Cerebrospinal fluid (CSF) analysis showed a slightly elevated cell count (6/μL; normal, <5/μL) and highly elevated protein (153 mg/dL). In addition, atypical cells were cytologically identified in the CSF. No other laboratory findings were abnormal. Emergency ventricular drainage was performed to control cerebral pressure, followed by a biopsy to confirm the diagnosis. Histological examination revealed a fascicular arrangement of oval cells with eosinophilic cytoplasm and tumor cells with pleomorphic nuclei and prominent nucleoli. Immunohistochemical studies showed negative results for glial fibrillary acidic protein and positive results for desmin and myogenin. In addition, molecular analysis revealed that this tumor had the H3F3A p.Lys28Met mutation and no paired box (PAX)3-forkhead box O1 (FOXO1) or PAX7-FOXO1 fusion genes. ARMS was, therefore, diagnosed. Chemotherapy and radiotherapy were subsequently initiated, but tumor growth could not be controlled, and the patient died 6 months after surgery. Conclusion: This report describes an extremely rare case of ARMS arising exclusively within the CNS.