Extraneural myxopapillary ependymomas in children: a case series and literature review

Background . Extraneural myxopapillary ependymomas (MPE) of the sacrococcygeal region are ultra-rare ependymal tumors with a marked pediatric predominance; no more than 36 pediatric cases have been reported in the world literature. Materials and methods . We performed a retrospective analysis of 5 pediatric patients with extraneural MPE diagnosed at the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology (Moscow) between 2015 and 2024. All patients were girls, the median age at diagnosis was 8.3 years (range – 4.9–15.3 years). Results . In 4 (80 %) of 5 patients, the tumor was located subcutaneously in the sacrococcygeal or intergluteal region; in 1 case it was presacral. A primary diagnostic error was recorded in 3 (60 %) patients, incorrect diagnoses were soft tissue sarcoma, primitive neuroectodermal tumor/immature teratoma, and clear cell ependymoma. All 5 tumors were morphologically consistent with MPE WHO grade 2 with diffuse GFAP expression. Molecular profiling by targeted gene expression profiling (NanoString technology) was performed in 4 of 5 (80 %) patients and confirmed the diagnosis of MPE in all cases. Radical resection was achieved in 4 patients (80 %); none of them developed recurrence. The single patient with R+ resection demonstrated disease progression. At a median follow-up of 43.0 months, all 5 patients are alive. Conclusions . Extraneural MPEs are characterized by a high rate of diagnostic errors and require mandatory histological review in a specialized reference center. Molecular genetic profiling using NanoString technology confirms the diagnosis and demonstrates the molecular relatedness of extraneural MPEs to their spinal counterparts. Radical resection is the key prognostic factor. Because of the risk of late metastatic spread, lifelong follow-up is required.