Retroperitoneal liposarcoma: MR characteristics and pathological correlative analysis.

BACKGROUND: Liposarcoma is the most common primary retroperitoneal malignant neoplasm. However, preoperative diagnosis is a common problem due to lack of characteristic clinical presentations. It has been assumed that MRI, based on its high soft-tissue resolution, could discover and discern different subtypes of this tumor. Moreover, there has been little in the literature to compare the MRI features with pathological appearances of the retroperitoneal liposarcomas.
METHODS: We retrospectively analyzed 19 cases of retroperitoneal liposarcoma (11 males and 8 females, aged 41-79 years) proved surgically and histologically. All patients underwent MRI examination before and after the administration of contrast agent. The MRI features and postoperative pathological appearances were studied correlatively.
RESULTS: Nine cases were located in the anterior pararenal space, four cases in the posterior pararenal space and six cases in the perirenal space. Among all cases, ten cases were present in the right retroperitoneum and nine cases in the left. The average diameter of the tumors was 14.7 cm (range from 7.5 cm to 26 cm). The MR signal intensity of liposarcoma was heterogeneous and varied greatly, depending on the components of the tumor and the different histological patterns. There are five subtypes of retroperitoneal liposarcoma. Myxoid liposarcoma (n = 7) exhibited low signal intensity on T1W image and high signal intensity on T2W image. On histologic analysis, myxoid liposarcoma consists of a myxoid matrix as the predominant component and small amounts of mature fat. Enhanced solid tissues and thickened septa of myxoid liposarcoma were seen on post-contrast image. Well-differentiated liposarcoma (n = 5) presented in high signal intensity on T1W images, intermediate signal intensity on T2W images, drop-out signal intensity on fat-suppressed MR images; The enhanced tenuous septa and solid tissues were seen on post-contrast image. Round-cell liposarcoma (n = 2) and pleomorphic liposarcoma (n = 2) exhibited soft-tissue tumor signal intensity without characteristic fat signal. One case of round-cell liposarcoma appeared with intratumoral hemorrhage and invaded the inferior vena cava. Dedifferentiated liposarcoma (n = 3) exhibited small amounts of fatty components with a clear demarcation between fat and nonadipose solid tissue on MR images. One case of dedifferentiated liposarcoma invaded the kidney.
CONCLUSION: MRI can clearly demonstrate shape, margin, internal components and surrounding tissues. Different subtypes of retroperitoneal liposarcoma exhibited varying MRI features, depending on tumor histological components. MRI should be an ideal method for diagnosing retroperitoneal liposarcoma.