The angular interface sign is used to characterise an exophytic renal mass, in which the exophytic renal mass has an angular interface with the renal parenchyma. In other words, the exophytic lesion has a tapered pyramidal contour or definite apex within the renal parenchyma.
Due to its high sensitivity and specificity, the angular interface sign is a strong predictor to identify lesions as either cysts, benign tumours, or as angiomyolipomas. It very rarely occurs with malignant lesions as renal cell carcinoma usually has a rounded interface with the renal parenchyma. It has high utility in differentiating between lipid-poor angiomyolipomas and renal cell carcinomas which contain intracellular lipids.
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