Comparison of MRI and Discography in Disc Extrusion: Low Signal Intensity Change in the Anterior Epidural Space at Sagittal T1-weighted Imaging

PURPOSE: To determine the significance of low signal intensity change in the anterior epidural space at sagittal T1-weighted (ST1WI) magnetic resonance imaging (MRI) of patients in whom discography revealed disc extrusion, and to correlate interruption of the solid dark line seen at sagittal T2-weighted imaging (ST2WI) with discographic findings of extrusion. MATERIALS AND METHODS: One hundred and forty-two patients (159 cases) with lumbar disc disease proven at MRI underwent discography. Disc extrusion was diagnosed in cases in which contrast media leaked into the anterior epidural space. The findings of ST1WI were used to determine whether low signal intensity change had occurred in the anterior epidural space between the posterior aspect of the vertebral body and the posterior longitudinal ligament, and whether ST2WI depicted interruption of the solid dark line at the posterior aspect of the disc was also assessed. RESULTS: At discography, disc extrusion was diagnosed in 134 of 159 cases. At ST1WI, low signal intensity change was noted in 75 (56%) of the 134 cases, and at ST2WI interruption of the solid dark line was observed in 63 (47%). In the remaining 25 cases, there was no evidence of disc extrusion, and at ST2WI the solid dark line was well-preserved. At ST1WI, 22 (88%) of 25 cases showed normal signal intensity in the anterior epidural space, but in the remaining three, low signal intensity change was evident. Correlation between the findings of MRI and discography was statistically significant. CONCLUSION: In disc disease, low signal intensity change at ST1WI, as well as interruption of the solid dark line seen at ST2WI, are useful indicators of disc extrusion.