Clinical History: 
This 20-year-old man presented with increasing pain and swelling in his left shoulder—an ongoing problem for the prior three months. Physical exam revealed a slightly tender, indurated mass with normal overlying skin.

Diagnosis:
Synovial sarcoma (monophasic fibrous type)

MR Technique: 
MR images were acquired at 1.5 T utilizing an 8-channel body coil. (A) axial pre-contrast spin echo T1-weighted (TR/TE 540/10 ms, 288×160 matrix) and (B) fast spin echo fat-suppressed T2-weighted (TR/TE 3900/41 ms) images were acquired in addition to (C) axial and (D)coronal post-contrast spin echo fat-suppressed T1-weighted images.

Imaging Findings:
A large irregular lesion demonstrating heterogeneous signal intensity is demonstrated in the region of left supraspinatus muscle. Foci of spared enhancement are noted within the body of the tumor, correlating with areas of necrosis and lending the lesion an appearance of heterogenous enhancement. There has been replacement of the normal marrow of the scapular spine which now demonstrates abnormally high signal intensity on T2 and low signal intensity on T1WI. Disruption of the low signal intensity bony cortex is also evident. Enhancement is present throughout portions of the adjacent musculature and soft tissue indicating involvement of these tissues.