Lumbar spine: postoperative assessment with surface-coil MR imaging.

A prospective study of 15 patients who were scheduled to undergo various types of lumbar spine surgery was undertaken to assess the postoperative changes observable with magnetic resonance (MR) imaging. Patients underwent imaging preoperatively, immediately postoperatively (1-10 days), and late postoperatively (2-6 months). A retrospective review of MR images obtained in 62 patients who had undergone lumbar surgery but still had low back pain was also conducted. Epidural soft-tissue change and mass effect mimicking preoperative findings were present in nine of 13 patients who underwent laminectomy and diskectomy. Mass effect improved in appearance by the late postoperative period in eight of nine patients. T2-weighted sagittal images were best in demonstrating the site of anulus disruption immediately after diskectomy, which was seen in 11 of 13 patients, and the rent resolved on the late images in eight of ten cases. Sites of foraminotomy were seen as a loss of the normal foraminal fat signal. Extensive soft-tissue changes present in the immediate postoperative period severely limit the usefulness of MR imaging in that period for evaluating persistent symptoms. The exception may be hemorrhage, as its distinctive signal on T1-weighted images makes its identification possible.