Posterior fossa ependymoma: a comprehensive review of molecular classification, management guidelines, and clinical outcomes (Part I of ependymomas across compartments).

PURPOSE: To review the clinical, molecular, and imaging landscape of posterior fossa (PF) ependymoma and outline current management principles guiding surgical and adjuvant treatment decisions. METHODS: We performed a narrative review of the contemporary literature on molecular classification, imaging characteristics, and treatment outcomes of PF ependymoma, focusing on distinctions between posterior fossa group A (PFA) and group B (PFB) tumors. RESULTS: PFA and PFB ependymomas are molecularly and clinically distinct. PFA tumors predominate in younger children, follow a more aggressive course, and show loss of H3K27me3, EZHIP overexpression, Moreover, in PFA tumors 1q gain and/or 6q loss defines a very high-risk group with increased recurrence and metastasis. PFB tumors arise more often in older patients, generally retain H3K27me3, harbor numerous arm-level chromosomal gains/losses, and carry more favorable outcomes. On MRI, PFA tumors more frequently show larger volume, hydrocephalus, lateral extension, skull base involvement, and lower apparent diffusion coefficient values. Gross total resection remains the most important prognostic factor and should be pursued whenever safe. Focal postoperative radiotherapy may be standard for localized disease, while chemotherapy has only a limited adjunctive role. Recurrence, especially among PFA tumors, is managed with early detection, repeat resection, and selective re-irradiation; 1q gain and 6q loss are enriched at relapse. CONCLUSIONS: PF ependymoma comprises two biologically and clinically distinct entities. Maximal safe resection and focal radiotherapy remain the backbone of treatment, but integrating molecular subgrouping, imaging biomarkers, and modern radiotherapeutic techniques into surgical and adjuvant planning offers the clearest path to improved outcomes, particularly for high-risk PFA tumors.