Tenosynovial giant cell tumor of the posterior arch of C1

Tenosynovial giant cell tumor, also called pigmented villonodular synovitis, is a disease typically of the joints and which uncommonly involves the spine. We present a case of a mass of the posterior C1 arch which eroded bone and did not arise from the facet joint. The imaging findings of spinal tenosynovial giant cell tumor will be reviewed as well as the imaging findings in this case, where tenosynovial giant cell tumor arose presumably within a small bursa. One’s understanding of the imaging characteristics can lead to the correct diagnosis and avoid an unnecessary work-up.