Retroperitoneal Malignant Triton Tumor in a 6-Year-Old Child Mimicking Wilms Tumor: A Case Report

Background: Malignant Triton tumor (MTT) is a rare, aggressive variant of malignant peripheral nerve sheath tumor (MPNST) featuring divergent rhabdomyoblastic differentiation. Comprising less than 5% of MPNST cases, MTT is associated with a poor prognosis, exhibiting a five-year survival rate of only 27.5%. Its occurrence in the pediatric retroperitoneum is exceedingly rare and frequently mimics more common malignancies, such as Wilms tumor. Case Presentation: A 6-year-old female presented with a four-month history of a painful right flank mass and lower limb functional impairment, without clinical stigmata of neurofibromatosis type 1 (NF1). Ultrasonography revealed a 349 mL vascularized retroperitoneal mass, leading to a provisional diagnosis of Wilms tumor. Exploratory laparotomy identified a tumor adherent to the vertebral column, necessitating intracapsular excision. Histopathological and immunohistochemical analysis confirmed MTT with rhabdomyoblastic differentiation and an immunoprofile suggestive of NF1 association. Despite palliative chemotherapy (cyclophosphamide and vincristine), the patient experienced rapid tumor recurrence and progressive clinical deterioration, culminating in death three weeks post-intervention. Conclusion: This case highlights the diagnostic complexity of pediatric retroperitoneal MTT, which can be clinically and radiologically indistinguishable from nephroblastoma. In resource-limited settings, where advanced molecular diagnostics are scarce, maintaining a high index of clinical suspicion and ensuring multidisciplinary management are paramount. Early histopathological confirmation is critical to addressing the rapid progression and therapeutic resistance characteristic of this malignancy.