Exophytic renal angiomyolipoma and perirenal liposarcoma: revisiting the role of CT for differential diagnosis

Background Exophytic renal angiomyolipoma and liposarcoma are two representative tumors in the retroperitoneum with fatty components that have potential to be misdiagnosed with each other. Purpose To compare the computed tomography (CT) findings of exophytic renal angiomyolipoma and perirenal liposarcoma. Material and Methods Fourteen and 16 cases with histologically-proven exophytic renal angiomyolipoma and perirenal liposarcoma, respectively, with preoperative CT from January 2000 to December 2013 were reviewed by two radiologists blinded to the clinical and pathological findings for an array of CT findings. These findings were compared between exophytic renal angiomyolipoma and perirenal liposarcoma using the Student t-test and Fisher’s exact test. Results Patients with exophytic renal angiomyolipoma were younger ( P = 0.001) without differences in sex ( P = 1.000). Exophytic renal angiomyolipomas were smaller ( P = 0.004) and more commonly showed the following findings: renal parenchymal defect ( P < 0.001), multiple linear vessels ( P = 0.026), aneurysmal dilatation of intratumoral vessels ( P = 0.024), renal parenchymal vascular pedicle ( P < 0.001), hemorrhage ( P = 0.037), encapsulated margin ( P = 0.001), and other intrarenal fatty lesions ( P = 0.037). No significant difference was seen in laterality, renal hilar vascular pedicle, non-fatty soft tissue nodule, calcification, or kidney displacement ( P = 0.236–1.000). Conclusion Several CT findings were significantly different between exophytic renal angiomyolipoma and perirenal liposarcoma and may be helpful for differentiating between the two entities when confronting a fatty mass in the perirenal space.