Fig 1.

Illustrations show development of lateral recess stenosis.

Column 1, congenital trefoil canal. The lateral recess region becomes progressively narrowed because of either facet or endplate-disk margin degenerative changes. Column 2, acquired trefoil canal. Early facet degenerative changes and hypertrophy in a triangular canal develops a trefoil shape with the root positioned in a lateral recess niche. Progressive disk margin, endplate, or further facet degenerative changes leads to compression of the trapped root. Column 3, acquired angular pinch of the lateral recess. Simultaneous near equal facet, endplate, and disk margin degenerative changes lead to acute angle formation in the corner of the canal and lateral recess region. The root becomes progressively compressed in the lateral recess and may be medially deflected. Column 4, bilateral acquired angular pinch of the lateral recess. Bilateral facet, disk margin, and endplate degenerative changes can narrow the central spinal canal and the lateral recess region. This can produce both central spinal stenosis with cauda equina compression and individual nerve root compression within the abnormal lateral recess.