Midline disk herniations of the lumbar spine.

Most lumbar disk displacements occur through the lateral fibers of the posterior longitudinal ligament, whereas only a small percentage occur through the strong midline fibers. The midline disk herniation is identified as a focal midline dural sac compression and is better seen on the lateral myelogram and computed tomography scan. Of the 22 patients in this study, 14 had midline lumbar disk herniations at L4-5. Their presenting symptoms including back pain with sciatica, were similar to those of lateral disk herniations. On physical examination, however, patients commonly had only positive root tension signs with few nerve root deficits. The incidence of cauda equina syndrome was 27%. The results of treatment were much poorer in these patients than results reported with lateral herniations; 41% were good, 27% fair, and 32% poor. Surgical decompression yielded the best results. A wide exposure is usually needed to provide adequate decompression.