Time-dependent scar enhancement in magnetic resonance imaging of the postoperative lumbar spine.

Magnetic resonance imaging (MRI) has become a principal modality in the evaluation of the post-operative lumbar spine. Gadolinium-diethylenetriamine-pentaacetic acid (Gd-DTPA) can often facilitate differentiation of scar from recurrent disc herniation according to established criteria. Scar has been believed to enhance predictably. We reviewed the contrast-enhanced MR scans of 44 patients who were examined for recurrent back pain following disc surgery and attempted to assess the enhancement characteristics of scar as a function of the time interval between initial surgery and the imaging study. In 44 patients, scar was believed to be present at 32 of 49 disc levels. The degree of enhancement was related to the postoperative interval; those studies performed no later than 9 months after surgery tended to exhibit the greatest degree of enhancement. Surgical confirmation of these MRI findings was available in 12 patients. In patients examined long after surgery, scar enhancement may be less intense than in those examined shortly after surgery, or even nonexistent. This temporal factor should be considered when using contrast material to differentiate scar from recurrent disc herniation in post-operative examinations of the lumbar spine.