Purpose: To assess whether or not MRI signal characteristics of lumbar disk herniations can predict subsequent disk regression.
Materials and methods: Medical and radiology records from 1999-2003 were reviewed, and 123 patients who had more than one lumbar MRI during the study interval were identified. Of these, 42 patients had a disk herniation (protrusion, extrusion, or free fragment) identified on their first examination. Six of the 42 patients were not included because of prior lumbar surgery, or inadequate examinations. The remaining 36 patients had a total of 77 examinations to evaluate 44 disk herniations. The herniated disks were evaluated by two CAQ neuroradiologists for size, morphology and a qualitative assessment of the T2 signal.
Results: Between the first and last examination, 25 of 44 (57%) herniated disks decreased, 17 (39%) were unchanged, and two increased in size. 9 of 11 (82%) of disk extrusions improved. The mean size of the disks that regressed was significantly larger than those that were unchanged (8.6 mm vs. 6 mm, p=.001). On average, the disks decreased 3.2 mm (37%). Of the disks that decreased in size, 15 (63%) had an area of increased signal on T2-weighted images (T2WI) compared to the parent disk on the initial study. Of the disks that were unchanged, 6 (35%) had increased signal on the T2WI's.
Conclusion: 57% of herniated disks in this study group decreased in size over time. Larger herniations and extrusions were more likely to regress than smaller herniations. Disks that regressed were more likely to have high signal on T2WI's than those that were stable.