Post-therapy neuronal maturation in adult medulloblastoma: a case report with literature integration.

Introduction: Post-therapy neuronal maturation (PTNM) is a rare phenomenon in medulloblastoma, in which a tumor that initially exhibits embryonal morphology acquires differentiated neuronal features after multimodal treatment. While several pediatric cases have been documented, reports in adults remain exceptional. Case presentation: We describe a 21-year-old woman who presented with headache, dizziness, and gait unsteadiness. MRI demonstrated a right cerebellar mass, and gross total resection revealed desmoplastic/nodular medulloblastoma (WHO grade 4) with high proliferative activity (Ki-67 ∼45% in internodular areas). She subsequently underwent craniospinal irradiation with a posterior fossa boost and multi-agent chemotherapy. Fourteen months later, surveillance MRI identified a recurrent posterior fossa lesion. Repeat resection showed a hypocellular nodular architecture within gliotic stroma, with diffuse synaptophysin and NeuN expression, strong neurofilament reactivity, partial GFAP positivity, and a markedly reduced Ki-67 index (1-2%). These findings were consistent with therapy-related neuronal maturation rather than true recurrence. No further adjuvant therapy was administered, and the patient remains alive and disease-free 40 months after initial diagnosis. Conclusions: This case provides additional evidence that post-therapy neuronal maturation can occur in adult medulloblastoma and may dominate the histological picture at recurrence. Accurate recognition of this endpoint preserves diagnostic continuity, prevents misclassification as a glioneuronal tumor, and emphasizes the need for larger adult series to clarify its prognostic significance and implications for long-term management.