Study Design. The present study retrospectively investigated the morphologic changes that occurred during conservative treatment of patients with unilateral leg pain resulting from herniated nucleus pulposus without significant lumbar canal stenosis. Objectives. The results were correlated with clinical outcomes and extruding forms to determine which type of herniated nucleus pulposus had the greatest capacity for spontaneous regression and how rapidly such regression might occur. Summary of Background Data. The study population consisted of 77 patients with radiculopathy, All patients complained primarily of unilateral leg pain, and 94% had positive tension signs. Additionally, 32% exhibited muscle weakness corresponding to the symptomatic nerve root. Methods. All patients were studied more than twice using magnetic resonance imaging during conservative therapy at a mean interval of 150 days. Morphologic changes on magnetic resonance imaging fell into four categories, with herniated nucleus pulposus classified into three types using T1-weighted sagittal views. Each patient was reexamined on the same scanner: 53 patients were examined twice, and 24 patients were examined more than three times. Results. Morphologic changes, with the exception of 13 false-negative cases, basically corresponded to clinical outcome, In half of the cases that showed some improvement at follow-up evaluation, improvement of clinical findings were seen before those observed on magnetic resonance imaging. Migrating herniated nucleus pulposus frequently presented an obvious decrease in size, and even disappearance in seven cases. The further the herniated nucleus pulposus migrated, the more decrease in size could be observed. The cases apparently corresponding to ''protrusion'' showed little or no change on follow-up magnetic resonance imaging. Regarding the mechanism of herniated nucleus pulposus disappearance, exposure to the vascular supply undoubtedly took a part, although many factors were suspected to have some influence. Conclusion. Morphologic changes on magnetic resonance imaging mainly corresponded to clinical outcomes but tended to lag behind improvement of leg pain. Disappearance of herniate nucleus pulposus was seen frequently in the cases of migrating disc herniation, and it was presumed that exposure to the vascular supply had a lot to do with this phenomenon.
