Successive changes in extraneural structures from the subarachnoid nerve roots to the peripheral nerve, influencing anesthetic block, and treatment of acute postoperative pain

The molecules deposited outside the nerve root, nerve root cuffs or nerve need to cross several structures before reaching the axons. The diffusion occurs initially through the tissue surrounding the nervous structures, then crossing and distributing among the intraneural area such as endoneurium, pia mater, arachnoid lamina, dura mater, fat tissue and transitional epithelium inside nerve root cuffs, epineurium, perineurium and endoneurium of peripheral nerve. The morphological characteristics of the tissue surrounding and protecting axons may change depending on the area and can influence the diffusion of local anesthetics to reach axons. The study of these morphological variables in depth will be of help to choose the best area of injection, according to the type of surgery and to analyze any possible complications.