Neuroblastomas (NBL) and nephroblastomas/Wilm's tumors (WT) represent two of the most commonly detected solid tumors in childhood 1. These are the two crucial differential diagnoses to be considered with any renal mass identified in a child of this age group 2.

Features strongly predictive of neuroblastoma on CT have also been seen in a significant number of patients with Wilm's tumors and this is highlighted by the case outlined above. Their disease sequelae, prognosis, management and potential complications are however vastly different and therefore not confusing or misdiagnosing one for the other is important.  This case, due to the overlap in similar radiological features of both WT and NBL, demonstrates how CT imaging, as important as its role is, only constitutes one part of the investigative spectrum and is not a gold standard modality in establishing a correct diagnosis 2

The mass identified on CT is heterogeneous in appearance which favors both diagnoses but with an irregular margin is more consistent with an NBL. A WT is typically well circumscribed, with smooth margins and often forms a pseudocapsule. No calcification is present within the mass. Calcifications and low attenuation necrotic areas are more common in 80-90% of NBLs whereas WTs present with calcifications in only 10-15% of cases3

A claw sign is present and favored to represent a WT. This refers to the delineated, sharp angles and margins on either side of a mass which the normal surrounding parenchymal tissue forms when the mass originates from the parenchyma 4.  

There is soft tissue, likely tumor extension into the left para-aortic position, displacing and partially compressing and encasing the abdominal aorta without invading it. There is extrinsic compression of the left renal vein but nil extension and nil invasion of the inferior vena cava. These features are typical of an NBL over a WT. WTs tends to extend into the renal vein and IVC whereas a NBLs often encases and displaces vessels 5.  

Additionally, the age group of 2 years is more suggestive of a likely NBL whereas WT affects slightly older children often aged between 3-4 yrs. 

Overall, features are mostly suggestive to represent an NBL but does have overlapping radiological features consistent with the presence of a WT. 

The patient was admitted overnight, received a blood transfusion and was transferred to an children's hospital under a Pediatric Oncology team for further investigations and arrangement of a biopsy to obtain a histopathological confirmatory diagnosis. 

She was found to have a high-risk neuroblastoma due to age, Nmyc amplication and extension of tumor and was commenced on chemotherapy per ANBL0532 Induction. Microscopic histopathology reports showed a small blue cell tumor growing as poorly formed nodules with a sheet-like architecture, with poor to moderate cohesion. The cells are hyperchromatic with fine chromatin and scant cytoplasm. There are focal areas of tumor necrosis. No calcification is present. Mitotic activity is easily identified. A bone marrow biopsy showed no disease present.