Asymmetrical muscle hypertrophy simulating a localised soft tissue mass.

Three children with a soft tissue mass presented to the Department of Radiology for investigation. Two children had a mass in the right axilla and the third had a mass overlying the right scapula. Cross-sectional imaging in each case revealed muscle hypertrophy rather than a discrete mass. The radiological diagnosis was later confirmed by histology. Minor asymmetry of muscles is quite common as a normal finding, but gross asymmetry of normal muscle is rare. Localised hypertrophy of muscle may result from exercise in children, but a history of excessive gymnastic exercise was apparent in only one child. The cause of the hypertrophy in the other two children is unknown.