Giant Cell Poor Extra-Articular Diffuse-Type Tenosynovial Giant Cell Tumor With Extensive Desmin Expression: A Potential Diagnostic Pitfall With Cytogenetic Confirmation.

Diffuse-type tenosynovial giant cell tumor can rarely present as an entirely extra-articular mass, which can be misdiagnosed as a sarcoma especially when giant cells are absent, dominated by large dendritic mononuclear cells, and desmin expression is extensive.