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