Muscle

Muscle tissue is composed of muscle fibers grouped into bundles called fascicles, each surrounded by connective tissue fascia. On ultrasound, muscle appears as hypoechoic or isoechoic linear or elliptical regions with characteristic fibrillar echotexture created by alternating interfaces between muscle fibers and connective tissue. The orientation of the transducer dramatically affects the appearance of muscle; longitudinal scanning shows parallel striations along the muscle fiber direction, while transverse scanning shows a speckled or honeycomb appearance. Sonographers must understand normal muscle anatomy to detect pathology such as tears, strains, and hematomas. Dynamic scanning that visualizes muscle contraction provides important functional information about muscle integrity and innervation.