Primary Intrarenal Neuroblastoma in an Infant Mimicking Wilms Tumor: A Rare Case Report and Diagnostic Dilemma.

Background: Primary intrarenal neuroblastoma (IRNB) is an exceptionally rare pediatric malignancy that can closely resemble Wilms tumor on clinical and radiologic evaluation, posing significant diagnostic and therapeutic challenges. Accurate differentiation between these two entities is critical, as their management strategies and prognostic profiles differ considerably. Case Presentation: We report the case of an 8-month-old male infant who presented with a progressively enlarging right-sided abdominal mass. Contrast-enhanced computed tomography revealed a large heterogeneously enhancing right renal mass with vascular encasement and intratumoral calcifications, findings that initially favored a diagnosis of Wilms tumor. The patient received preoperative chemotherapy in accordance with the SIOP protocol, followed by radical nephrectomy. Histopathologic examination of the resected specimen demonstrated a poorly differentiated neuroblastoma characterized by Homer-Wright rosettes, neuropil formation, and salt-and-pepper nuclear chromatin. Immunohistochemical analysis showed diffuse synaptophysin positivity and absence of WT1 expression, confirming the diagnosis of primary intrarenal neuroblastoma. The patient subsequently received neuroblastoma-directed chemotherapy and achieved complete remission. Conclusion: Primary intrarenal neuroblastoma is a rare but important differential diagnosis of renal masses in infancy, particularly when imaging reveals atypical features, such as vascular encasement and intratumoral calcifications, or when there is a suboptimal response to Wilms tumor-directed chemotherapy. Because of its significant clinical and radiologic overlap with Wilms tumor, preoperative diagnosis remains challenging. In patients with atypical findings, tissue diagnosis by core needle or open surgical biopsy, followed by histopathologic and immunohistochemical evaluation, should be considered before initiating empiric chemotherapy. Early multidisciplinary assessment is essential for accurate diagnosis and appropriate management.