Renal Ewing Sarcoma Mimicking Neuroblastoma: A Multitracer PET/Scintigraphic Imaging Pitfall

Area of Science:

• Pediatric Oncology
• Nuclear Medicine
• Diagnostic Imaging

Background:

• Renal Ewing sarcoma (EWS) is a rare pediatric malignancy.
• It can present as a suprarenal mass, mimicking neuroblastoma on conventional imaging.
• Diagnostic challenges arise due to its rarity and potential for imaging overlap with other pediatric tumors.

Purpose of the Study:

• To highlight the diagnostic utility of multimodality nuclear imaging in a case of pediatric renal Ewing sarcoma.
• To emphasize the importance of considering renal EWS in cases with discordant imaging findings.
• To illustrate the role of advanced PET/CT techniques in differentiating rare pediatric renal masses.

Main Methods:

• Case report of a 6-year-old boy with a suprarenal mass.
• Utilized I-131 metaiodobenzylguanidine (mIBG) scintigraphy, Ga-68 DOTANOC PET/CT, and F-18 FDG PET/CT.
• Performed repeat biopsy with fluorescence in situ hybridization (FISH) for EWSR1 gene rearrangement confirmation.

Main Results:

• Initial biopsy was inconclusive; mIBG scintigraphy showed no uptake.
• Ga-68 DOTANOC PET/CT revealed mild somatostatin receptor expression.
• F-18 FDG PET/CT demonstrated intense hypermetabolism, indicating a discordant molecular imaging profile.
• FISH confirmed EWSR1 gene rearrangement, diagnosing renal Ewing sarcoma.

Conclusions:

• Multimodality nuclear imaging is valuable for diagnosing pediatric renal masses.
• An mIBG-negative, intensely FDG-avid lesion with low somatostatin receptor expression should raise suspicion for renal EWS.
• Re-evaluation of histopathology is essential when imaging findings are discordant.