Renal Angiomyolipomas: Radiologic Classification and Imaging Features According to the Amount of Fat
Angiomyolipoma (AML), which is histologically composed of fat, muscle, and vessel, is the most common benign solid renal tumor. Most AMLs are easily diagnosed because of abundant fat that is measured -10 HU on CT. However, some AMLs are difficult to identify due to a small amount of fat. This type of AML is variously named, so that there have been different results between investigations. Accordingly, readers or investigators are confused to understand the radiologic classification of AML.
Recently, two articles have reported the radiologic classification of AML. When CT or MR images are interpreted, one requires several kinds of non-radiological information. However, the other requires quantitative CT or MRI measurements alone to determine whether or not there is fat in a lesion. Therefore, the latter classification appears feasible in classifying AML according to the amount of fat. It may avoid confusion of various terminologies indicating AML with a small amount of fat.
The purpose of our review was to introduce the radiologic classifications of AML and the clinical implications for patient care, to show imaging features of each type of AML, and to describe what type of AML should be biopsied to differentiate from renal cell carcinoma.
Keywords: Kidney; Angiomyolipoma; Ultrasonography; Computed tomography; Magnetic resonance imaging
1. Renal AML can be classified according to the amount of fat.
2. AML’s fat can be quantified with CT or MRI measurements.
3. The types of AML include fat-rich, fat-poor, and fat-invisible AML.
4. Each type of AML shows unique US, CT, and MRI features.
5. Inappropriate location or size of a ROI leads to mis-classifying AMLs.