A classic angiomyolipoma (AML) has abundant fat and therefore appears hyperechoic on a sonogram, similar to the sinus fat. Acoustic shadowing may be seen in up to a 3^rd of the lesions. Unlike stones, these lesions do not typically exhibit twinkle artefact on color Doppler. Definitive diagnosis of AML is possible only by CT or MRI because they ‘diagnose’ fat and ultrasound can only ‘suggest’ fat. On non-contrast CT scan, the presence of regions of interest containing attenuations less than -10 HU allows confident identification of fat. Following are some examples of classic AMLs.

In patients with tuberous sclerosis, multiple renal AMLs are seen and often difficult to characterize on ultrasound. Corticomedullary differentiation is typically lost. Management should be guided by CT or MRI in such cases. Following is an example.

Small, well circumscribed bright lesions can be followed by ultrasound alone while any suspicion for malignancy warrants CT or MRI. The following lesion looks hyperechoic and most likely is AML but I would get a CT if possible because it’s more hypoechoic compared to sinus fat.

Renal cell carcinomas are hypoechoic to heterogeneous. They can be isoechoic also, which can be easily missed on quick scans. Therefore, it is important to image kidneys from multiple scan planes. Hardly takes an additional minute of your time! In addition, if you see anechoic rim surrounding the lesion or intralesional cysts or calcifications, think renal cell carcinoma. Following are some examples of RCC.

“Fat-poor AMLs” can be of heterogeneous echotexture or just isoechoic to renal parenchyma. It is challenging to differentiate them from malignancy and therefore, almost always require further imaging.