Sonographically, Grade I muscle strains may have a normal appearance, or show focal or general areas of increased echogenicity. Perifascial fluid may be seen, and up to 50% of muscles with Grade I strains show generalized hyper-echogenicity on ultrasound . On ultrasound, Grade II strains show discontinuity of muscle fibers, with hypervascularity around the disrupted muscle fibers . An intramuscular fluid collection may also be seen with a surrounding hyperechoic halo. Grade III injuries at sonography often show complete discontinuity of muscle fibers and associated hematoma . Sonographic findings can distinguish Grade I from Grade II strains (Fig. 14), both of which have similar hyperintensity on T2-weighted MR images ; however, others have reported that sonography may not be as accurate as MRI in assessing muscle strains, because it may be difficult to depict the normal hyperechoic intramuscular portion of the tendon after injury .
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