[Renal angiomyolipomas: atypical aspects in ultrasonography and computerized tomography]

As a rule, renal angiomyolipomas (AML) present with characteristic patterns on US and CT images. However, in a limited number of cases US and CT findings are atypical, so that no diagnosis can be made on their basis. The authors reviewed their personal series of renal tumors and now report the US and CT findings of 5 cases with atypical features on one or both examinations. Two patients had hyperechoic lesions with typical AML patterns, but no fatty densities were visible with CT. Both patients underwent surgery and histology which showed two AMLs with muscular and vascular components and very few fatty cells. Two cases were observed in patients with Bourneville disease. Even though the cases exhibited atypical features on US and CT images, the diagnosis was suspected on the basis of the well-known association of tuberous sclerosis with AML. One case presented with a complex cystic mass on US; CT showed a bleeding tumor. Even though no unquestionable diagnosis of AML could be made in this case, the hypothesis of a bleeding AML was considered in the differential diagnosis. Such atypical imaging features were related to low fatty content inside the lesion and to bleeding complications. Absent/low fatty component represented a cause of atypical lesion appearance on CT which showed a mass with soft-tissue density which could not be differentiated from a solid tumor. In these cases, AMLs remained typically hyperechoic on US images. Bleeding represented a cause of error mainly on US since the typical hyperechoic pattern was replaced by a iso-hypoechoic pattern. CT is helpful in these cases because it shows both the bleeding and possible low-density fatty areas.