腎被膜から発生した筋脂肪腫の1例

Abstract

78歳女性。患者は高血圧および糖尿病で近医へ通院中, 腹部超音波にて左腎下極背側の腫瘤を指摘され, 精査加療目的で著者らの施設へ紹介入院となった。臨床検査では異常所見は認められなかったものの, CTおよびMRIでは腎被膜由来の腫瘍, または後腹膜腫瘍が強く疑われた。後腹膜鏡下腎部分切除術を施行した結果, 術中迅速病理では悪性所見はみられず, 病理組織学的に腎被膜から発生した筋脂肪腫と診断された。現在, 術後1年6ヵ月経過で再発はみられていない。

A 53-year-old female visited us with an asymptomatic renal mass, which was incidentally found on abdominal ultrasonography (US). US showed a heterogeneous renal mass measuring 5 cm in diameter. Computed tomorraphy and magnetic resonance imaging showed that the tumor was mixed with muscle and fat tissue, faintly enhanced, and located at the lower portion of the left kidney. Although renal angiomyolipoma (AML) was suspected from these findings, we could not rule out a malignant tumor. Therefore, she underwent a laparoscopic partial nephrectomy. Histopathological examination revealed the tumor composed of smooth muscle and mature adipose tissue without cytological atypia arising from the renal capsule. The tumor contained no AML-like blood vessels, and was negative for HMB-45 staining. The final diagnosis was myolipoma arising from the renal capsule. Myolipoma is a rare benign neoplasm in the soft tissue of retroperitoneum and abdominal cavity. Since it is difficult to distinguish myolipoma from other benign and malignant tumors with fat tissue only by imaging studies, a surgical approach should be considered.