[Unilateral spondylolysis with spina bifida occulta of lumbar spine--case report and review of the literature].

Unilateral spondylolysis and midline defects in the posterior spinal elements attributable to spina bifida occulta (SBO) result in the unilateral floating of the vertebral arch. We report a patient with unilateral spondylolysis associated with SBO in the lumbar spine and review the literature. This 71-year-old male experienced severe left leg pain and lumbago that worsened upon walking. Radiographic studies revealed SBO and unilateral spondylolysis of L5. The dural sac and left L5 nerve root were compressed by the organization of tissues around the spondylolysis. As his symptoms failed to respond to conservative treatment, he underwent unilateral laminectomy without fusion. At operation, the left lamina of L5 was floating and unstable; the right lamina was stable. Medial facetectomy at L4/5 and excision of the left floating lamina of L5 were performed. For satisfactory decompression of the dural sac and left L5 nerve root, the cartilaginous fibrous tissue around the lysis was removed. His symptoms disappeared immediately after surgery. Although long-term follow-up is necessary, we suggest that unilateral microdecompression without fusion is a useful method to treat patients with unilateral spondylolysis with SBO.