[A Case of Retroperitoneal Liposarcoma in which Magnetic Resonance Imaging was Useful in the Decision of Resection of Primary and RecurrentTumors].

A 47-year-old female was referred to our hospital because of retroperitoneal tumor which was detected by computer tomography (CT). Since the tumor was considered to be benign by magnetic resonance imaging (MRI), she was followed by MRI every 3 months. The site of the tumor was gradually increased, and 15 months after presentation, a lesion with high signal intensity on diffusion weighted image (DWI) appeared in the tumor. At that time, we performed tumor resection considering the tumor to be malignant. Pathological diagnosis was dedifferentiated liposarcoma. Three years and two months after the operation, liposarcoma recurred in the left retroperitoneal space. Because it showed low signal intensity on DWI, which was compatible with well-differentiated liposarcoma, further follow-up was carried out. Eleven months after the recurrence, a lesion with high signal intensity on DWI appeared in the tumor. We performed tumor resection again, leading to pathological diagnosis of recurrence of dedifferentiated liposarcoma. She remained free of disease at 4 months after surgery.