Objective To investigate the sonographic characteristics of the primary retroperitoneal sarcoma. Methods Ultrasonographic features of 47 patients with primary retroperitoneal sarcoma confirmed by biopsy or surgical pathology were retrospectively analyzed. Results Among all 47 primary retroperitoneal sarcomas

single lesion was found in 42 cases

while multiple lesions were found in 5 cases. Pathology confirmed 29 cases of liposarcoma

13 cases of leiomyosarcoma

4 cases of rhabdomyosarcoma

and 1 case of ewing’s sarcoma. The diameters of all tumors were 2.0-55.0cm

average 14.3±9.6cm. There were 32 cases presented hypoechoic

8 cases with hyperechoic and 7 cases with complex echoic. Sixteen tumors were inhomogeneous

12 cases were accompanied with no-echo areas

and 5 cases with calcification in the tumor. Well-defined boundary of tumors was found in 26 cases

and ill-defined boundary of tumors were found in the other 21 cases. Regular shape of tumors was found in 15 cases

while the other 32 cases were presented as irregular shape. Color Doppler flow imaging (CDFI) showed abundant tumor blood flow signals in 35 cases

and no obvious blood detected in the other 12 cases. In addition

18 tumors invaded peripheral organs with different degrees

four cases accompanied with retroperitoneal lymph node metastasis

and 1 case with tumor thrombosis in bilateral common iliac vein and inferior vena cava. Conclusion Primary retroperitoneal sarcomas are usually present as large size

and grayscale ultrasound usually showed as well-defined hypoechoic masses with irregular shape in the retroperitoneum. Necrotic liquefaction areas or patchy calcification can be seen in some tumors

and abundant tumor blood flow signals can be detected in majority of retroperitoneal sarcomas on CDFI.