Final answer:
Normal kidneys have smooth outer contours and no echoes of perirenal fat.
Step-by-step explanation:
The characteristics of normal kidneys include:
- Smooth outer contours surrounded by reflected echoes of perirenal fat: The kidneys have a smooth outer surface and are surrounded by a layer of fat called the perirenal fat, which can be seen as echoes on ultrasound.
- Irregular outer contours with no echoes of perirenal fat: This is not characteristic of normal kidneys. Irregular outer contours may indicate an abnormality or disease.
- Smooth outer contours with no echoes of perirenal fat: This is characteristic of normal kidneys. The outer surface of the kidneys is smooth, and there are no echoes of perirenal fat.
- Irregular outer contours surrounded by reflected echoes of perirenal fat: This is not characteristic of normal kidneys. Irregular outer contours may indicate an abnormality or disease, and the presence of reflected echoes of perirenal fat is also abnormal.