Neuroblastoma Presenting as a Congenital Renal Mass in a Neonate: A Diagnostic Pitfall.

Congenital renal masses in neonates are most commonly congenital mesoblastic nephroma or, less frequently, or Wilms tumor. We describe a neonate with an apparent primary renal tumor that proved to be adrenal neuroblastoma infiltrating the kidney, highlighting diagnostic pitfalls in this subgroup of patients. We retrospectively reviewed the diagnostic work-up, histopathology, genomic profiling, treatment, and outcome of a term neonate in whom a renal mass was detected incidentally on ultrasound. Ultrasound and MRI showed a 2 cm solid lesion centered in the upper pole of the left kidney, interpreted as nephroblastomatosis/early Wilms tumor. Left nephrectomy with adrenalectomy revealed stroma-poor, undifferentiated neuroblastoma with regional node involvement and multiple segmental chromosomal aberrations, including 1p and 3p loss, but no MYCN or ALK alterations. Initial management consisted of surgery alone with close surveillance. Within weeks, early disseminated relapse with bone and soft-tissue metastases occurred, necessitating escalation to high-risk, COJEC-based chemotherapy; resection of residual mass; and modified consolidation without high-dose chemotherapy or radiotherapy. The child remains in complete remission with preserved renal function. Neuroblastoma should be considered in the differential diagnosis of congenital "renal" masses. Imaging-driven provisional diagnoses may be misleading, and genomic risk profiling may help lower the threshold for systemic therapy in selected cases.