What is the normal sonographic appearance of various soft tissues (skin, subcutaneous fat, fascia, cortical bone, hyaline cartilage, fibrocartilage, and muscle)?
The epidermis and dermis of the skin typically appear as a thin hyperechoic layer. Subcutaneous fat is hypoechoic with thin linear echogenic septations paralleling the skin surface. Fascia appears as a thin, linear hyperechoic layer with variable thickness. Cortical bone is very hyperechoic with posterior acoustic shadowing. Hyaline cartilage, which covers the articular surface of bone, is uniformly hypoechoic. This is in contrast to the fibrocartilaginous labrum and meniscus, which are hyperechoic ( Figure 63-3 ). Normal muscle tissue appears relatively hypoechoic with interspersed hyperechoic fibroadipose septa; in long axis, normal muscle has a pennate, or featherlike, appearance. In short axis, muscle demonstrates a characteristic “starry sky” appearance