Extra-articular diffuse-type tenosynovial giant cell tumor (TSGCT), especially arising from the pes anserine bursa, is a rare lesion. Only one case of extra-articular diffuse-type TSGCT of the pes anserine bursa that showed bone erosion as an imaging finding has been reported. Here, we report our experience of an exceptional case of extra-articular diffuse-type TSGCT of the pes anserine bursa with intramedullary extension into the tibia on magnetic resonance imaging, which resembled a benign soft tissue mass on radiography, along with a review of the literature.
