Primary Intrarenal Neuroblastoma in a Four-Month-Old Infant: A Rare Diagnostic Challenge Mimicking Wilms Tumor.

Primary intrarenal neuroblastoma is an exceedingly rare entity that often mimics Wilms tumor in clinical and radiologic presentation, making prompt differentiation crucial given their divergent treatment pathways and prognostic implications. We present the case of a four-month-old male infant incidentally discovered to have a right-sided abdominal mass. Imaging suggested a renal malignancy, most likely Wilms tumor, but urgent surgical intervention was required due to intralesional bleeding and a precipitous drop in hemoglobin. Elevated urine catecholamine metabolites (homovanillic acid and vanillylmandelic acid) were subsequently detected, but only after the decision for surgery. Intraoperatively, the mass was confirmed to arise from the renal parenchyma rather than the adrenal gland. Pathologic examination revealed sheets of small round blue cells positive for chromogranin, synaptophysin, and cluster of differentiation 56, establishing the diagnosis of neuroblastoma. Four lymph nodes were positive for metastatic involvement, but there was no amplification of the MYCN oncogene. Postoperative urinary catecholamine metabolite levels normalized, and follow-up imaging demonstrated no residual disease at ten months. This case highlights the importance of considering primary intrarenal neuroblastoma in the differential diagnosis of pediatric renal masses and underscores the need for comprehensive imaging and laboratory evaluation to guide appropriate surgical management and postoperative surveillance.