Nerve Injury 11/04/2024 PDF

Peripheral Nerve Injury 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling  Definition: Wallerian degeneration is a process Wallerian that results when a nerve fibre i...

Peripheral Nerve Injury 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling  Definition: Wallerian degeneration is a process Wallerian that results when a nerve fibre is cut or crushed, in which the part of the axon separated from the degenerati neuron's cell nucleus degenerates. This is also known as anterograde degeneration. on 11/04/2024 ITC Pathology of Injury M Dowling  Classification System Seddon (1943) Classification of nerve injuries based on three main types of nerve fiber injury and whether there is continuity of the nerve Neuropraxia Axonotmesis Neurotmesis 11/04/2024 ITC Pathology of Injury M Dowling  Neuropraxia (mildest injury) There is an interruption in conduction of the impulse down the nerve fiber, and recovery takes place without wallerian degeneration. Mildest form of nerve injury Biochemical lesion caused by concussion or shock- like injuries to the fibre. 11/04/2024 ITC Pathology of Injury M Dowling  Neuropraxia is brought about by compression or relatively mild, blunt blows, including some low- velocity missile injuries close to the nerve. There is a temporary loss of function which is reversible within hours to months of the injury ( the average is 6-8 weeks ). There is frequently greater involvement of motor than sensory function with autonomic function being retained. 11/04/2024 ITC Pathology of Injury M Dowling  11/04/2024 ITC Pathology of Injury M Dowling Axonotmesis (moderate injury) Involves loss of the relative continuity of the axon and its covering of myelin, but preservation of the connective tissue framework of the nerve ( the encapsulating tissue, the epineurium and perineurium, are preserved ). Because axonal continuity is lost, wallerian degeneration occurs. Recovery occurs only through regeneration of the axons, a process requiring time. 11/04/2024 ITC Pathology of Injury M Dowling  Axonotmesis is usually the result of a more severe crush or contusion than neuropraxia. Proximal lesion may grow distally as fast as 2 to 3 mm per day and distal lesion as slowly as 1.5 mm per day. 11/04/2024 ITC Pathology of Injury M Dowling Neurotmesis More severe lesion with least potential of recovery. Occurs on severe contusion, stretch, lacerations. The encapsulating connective tissue lose their continuity. The last (extreme) degree of neurotmesis is transsection, but most neurotmetic injuries do not produce gross loss of continuity of the nerve but rather: the internal disruption of the architecture of the nerve sufficient to involve perineurium and endoneuruim as well as axons and their covering. 11/04/2024 ITC Pathology of Injury M Dowling  Neurotmesis Denevertion changes recorded by EMG are the same as those seen with axonotmetic injury. There is a complete loss of motor, sensory and autonomic function. If the nerve loss has been completely divided, axonal regeneration causes a neuroma to form in the proximal stump. For neurotmesis its better to use a new classification, more complete, called Sunderland System 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling Sunderland System 1951 First-degree: "Seddon’s neuropraxia": nerve in continuity, compression or ischemia - local conduction block, focal demyelinization may occur, recovery is usually complete in 2- 3 weeks ( not the ‘1mm/day’ rule ). Second-degree: "Seddon’s axonotmesis": injury to axon, supporting structures (including endoneurium ) intact; wallerian degeneration occurs; recovery at 1mm/day as axon follow ‘tubule’, sometimes most only be diagnosed retrospectively, recovery is poor in lesions requiring >18 months to reach the target muscle. 11/04/2024 ITC Pathology of Injury M Dowling  Third-degree: endoneurium disruptured, epineurium & perineurium intact: recovery may range from poor to complete and depends on degree of intrafascicular fibrosis; nerve may not appear seriously damaged on gross inspection. Fourth-degree: interruption of all neural and supporting elements; epineurium intact; the nerve is usually enlarged. Fifth-degree: complete transection with loss of continuity 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling 11/04/2024 ITC Pathology of Injury M Dowling Surgery The goal in fixing the nerve is to repair the outer cover so that nerve fibers can grow down the empty tubes to the muscles and sensory receptors and work again. The surgeon tries to line up the ends of the nerve repair so that the fibers and empty tubes match up with each other as best as possible, but with millions of fibers in the nerve, not all of the original connections are likely to be re-established. If a wound is dirty or crushed, they may wait to fix the nerve until the skin has healed. 11/04/2024 ITC Pathology of Injury M Dowling  Refs Sunderland, S.,(1951) A classification of peripheral nerve injuries producing loss of function. Brain, 1951. 74: p. 491-516. Seddon, H., (1943). Three types of nerve injuries. Brain, 1943. 66: p. 237 11/04/2024 ITC Pathology of Injury M Dowling