Primary Renal Undifferentiated Sarcoma as an Infiltrative Mass in a 12-Year-Old Boy

Abstract

Undifferentiated sarcomas are rare tumors not classified into any sarcoma subtype. Due to their rarity, imaging findings of undifferentiated sarcomas are poorly characterized. The purpose of this report was to present imaging findings of a pathologically confirmed undifferentiated sarcoma originated from the left kidney of a 12-year-old boy. The mass was infiltrative involving the renal pelvis. It mimicked massive hilar lymphadenopathy with a preserved renal contour visible by both ultrasonography and CT. Renal vein thrombosis was also observed. Although undifferentiated sarcomas are rare, they should be considered in differential diagnosis of infiltrative renal masses with renal pelvis invasion in children.