The ultrastructure of the human spinal nerve root cuff in the lumbar spine.

BACKGROUND Spinal nerve root cuffs may be relevant in selective nerve root and epidural blockade. METHODS We examined the ultrastructural aspects of spinal nerve root cuffs, such as their cellular and fibrillar components, using special histological staining methods, transmission and scanning electron microscopy, from six human cadavers. RESULTS The morphology of the spinal nerve root cuff resembles that of the spinal subdural compartment. Cells gather together in compact layers due to specialized junctions. The thickness of its cellular layers is 5 to 8 microns; cells appear oriented parallel to the direction of their own nerve roots. The fibrillar component, made largely of collagen fibers, is found in the outer part of the spinal nerve root cuff and measures 100 to 150 microns. Numerous adipocytes separate dural laminas in concentric layers, extending from the dural sac to the spinal nerve root ganglia. However, adipocytes are not found within the thickness of the dural sac. CONCLUSIONS The presence of few capillaries and the short distance between fat and axons may affect the passage of epidurally injected substances towards nerve root axons.