Central lumbar stenosis caused by ligamentum flavum: unilateral laminotomy for bilateral ligamentectomy: preliminary report of two cases.

Degenerative central lumbar stenosis has traditionally been considered to be a result of bony narrowing of the spinal canal. In two consecutive patients with degenerative central lumbar stenosis and complete myelographic blocks, the cauda equina was compressed by a thickened ligamentum flavum (cross-sectional area [CSA], > 150 mm2). This ligamentous stenosis occurred within bony canals of normal dimensions (anteroposterior diameter, interpediculate distance, interfacet distance, and CSA). High-resolution computed tomographic myelography was used to calculate quantitative values for the CSA, the length, and the volume of the lumbar ligamentum flavum. Excision of the thickened ligamentum flavum restored the dural sac to normal (CSA, 130-230 mm2), and both patients received relief from their symptoms. Unilateral laminotomy was used successfully to achieve bilateral ligamentectomy. Therefore, in a well-defined subgroup of patients with degenerative central lumbar stenosis, the dural sac can be decompressed by selective resection of the ligamentum flavum, and bilateral ligamentectomy can be performed via unilateral laminotomy.