Magnetic resonance imaging of a thoracic intraspinal synovial cyst.

A 50-year-old woman presented with mid-thoracic back pain that radiated to the left rib cage in a radicular manner. Magnetic resonance imaging revealed an extradural mass compressing the left T9 nerve root. The mass was adjacent to a degenerated T9-10 facet joint with an enhancing low signal intensity rim. Recognition of the characteristic imaging findings of an intraspinal synovial cyst resulted in the correct preoperative diagnosis despite the unusual location of this lesion at T9-10.