Retroperitoneal Myolipoma with Hip Invasion: A Case Report

: Background and Clinical Significance: Myolipoma is a rare benign tumor, typically found in the retroperitoneum and characterized by a combination of mature adipocytes and well-differentiated smooth muscle cells. Myoplipomas usually present a delay in diagnosis due to the painless and slow-growing clinical behavior; therefore, the lesion can reach a large dimension with 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. Histological examination revealed mature adipose tissue infiltrating smooth muscle cells. 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.