Clinical History: 
This 28-year-old man presented with increasing pain and swelling in his right shoulder for more than four months. Physical exam revealed an obvious swelling, with overlying normal skin, involving the right shoulder. Because of the swelling and pain, movement of the joint was restricted.

Diagnosis:
Osteosarcoma

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

Imaging Findings:
A large irregular lesion is demonstrated involving the right shoulder. The upper humerus is invaded with abnormal high T2WI signal intensity in bone marrow, discontinuity of bone cortex and a large lobulated soft tissue tumor surrounding the right humerus. The soft tissue mass has heterogenous signal intensity and extends into the adjacent muscles and connective tissues, which also demonstrate prominent contrast enhancement. The areas of low signal intensity on post contrast T1WI inside the soft tissue portion of the tumor represent necrotic regions, which makes the whole soft tissue mass have a heterogeneous enhancement appearance.