[Imaging findings of primary sarcoma in the kidney]

To reveal the characteristic findings of primary sarcoma of the kidney.

From December 1988 through February 1996, seven cases of renal sarcoma confirmed by histo-pathology were retrospectively reviewed, including 3 leiomyosarcoma and 1 for each of liposarcoma, fibrosarcoma, malignant fibrous histiocytoma and malignant Schwannoma. Image material: CT in 6 cases, ultrasonography in 6 cases and MRI in 1 case.

The tumor was located in renal parenchyma in 6 cases and in renal pelvis in 1 case. On the images, it was commonly a large mass with irregular margin, indefinite, circumscribed and heterogeneous in density with necrosis inside as observed on the CT scan and 2 cases with median to hyperattenuation on the enhanced CT scan; 4/6 cases gave median heterogeneous mixed echo and 2/6 cases appeared as even hypoechoic mass on the ultrasonogram. On MRI, the mass gave isosignal intensity on T1WI and increased signal intensity with moderate heterogeneity was seen on T2WI or became more enhanced and heterogeneous but no more than renal parenchyma on the enhanced T1WI of MRI. Big tumor thrombus in the inferior vena cava and renal vein was noted in the fibrosarcoma.

Primary renal sarcomas give imaging findings characteristic of malignant tumor but without histological specificity and can not be differentiated from renal cell carcinoma. The enhanced CT and MRI capable of providing useful information of the localization, changes in density/signal and extent of invasion of the tumor, are beneficial to the differential diagnosis and managements.