Retroperitoneal Myolipoma with Hip Invasion

Background: and Clinical Significance: Myolipoma is a rare benign tumor, typically found in the retroperitoneum and characterized by a combination of mature adipo-cytes and well-differentiated smooth muscle cells. Myoplipomas usually present a de-lay in diagnosis due to the painless and slow growing clinical behaviour; therefore, the lesion can reach a large dimension with a challenging treatment. Case Presentation: We present the case of a retroperitoneal myolipoma infiltrating the left hip of an 11-year-old male. It was suspected based on magnetic resonance imaging; The patient has been successfully treated with surgical excision without complications. Histologi-cal examination revealed mature adipose tissue infiltrating skeletal striated muscle. The muscle fibers appeared normal, while the dense connective tissue was infiltrated by clusters of mature lymphocytes. Conclusions: Although myolipoma is extremely rare in male children and has never been reported to infiltrate the hip, it should be considered in the differential diagnosis of fat-containing retroperitoneal masses.