Intramuscular diffuse-type tenosynovial giant cell tumor of the deltoid muscle in a child.

Tenosynovial giant cell tumors (GCTs) typically form in the joints or extra-articular soft tissues such as the tendon sheath, and are benign tumors that commonly occur in the hands or wrists in the third to fifth decades of life. However, the diffuse type of extra-articular GCT arising within muscle is a rare soft tissue tumor, especially in a pediatric patient. In this report, we describe the magnetic resonance imaging and sonographic findings of a rare case of intramuscular diffuse-type GCT in the deltoid muscle of a 9-year-old boy.