Figure 11b. Cystic change in retroperitoneal leiomyosarcoma caused by chemotherapy in a 63-year-old woman. (a) Contrast-enhanced CT scan obtained before chemotherapy shows a large, lobulated soft-tissue mass with an attenuation value of 65 HU in the left anterior pararenal space (arrow). (b) On a contrast-enhanced CT scan obtained 6 months after chemotherapy, the mass (arrow) is hypoattenuating (20 HU) and decreased in size.