目录
神经损伤的分类
神经损伤可以分为三类：
- Neurapraxia
Neurapraxia, the least severe form of peripheral nerve injury, is a contusion of a nerve in which continuity of the epineural sheath and the axons is maintained
- Axonotmesis
Axonotmesis has occurred when the continuity of the axons, but not the epineural sheath, is disrupted.
- Neurotmesis
Neurotmesis, the most severe type of nerve injury, involves a complete loss of nerve continuity.
其他分类方式包括：Sunderland grading (I to V) and the Medical Research Council Scale等。
神经损伤的愈合
包括两个阶段：(1) degeneration and (2) regeneration.
其中Degeneration阶段包括两种类型：Segmental demyelination 和 Wallerian degeneration
(1) Segmental demyelination in which the myelin sheath is dissolved in isolated segments. This partial demyelination causes a slowing of conduction velocity and may prevent the transmission of some nerve impulses. Symptoms include paresthesia (a spontaneous and subjective altered sensation that a patient does not find painful), dysesthesia (a spontaneous and subjective altered sensation that a patient finds uncomfortable), hyperesthesia (excessive sensitivity of a nerve to stimulation), and hypoesthesia (decreased sensitivity of a nerve to stimulation). Segmental demyelination can occur after neurapraxic injuries or with vascular or connective tissue disorders and may undergo spontaneous regeneration.
(2) Wallerian degeneration. In this process, the axons and myelin sheath of the nerve distal to the site of nerve trunk interruption undergo disintegration in their entirety. The axons proximal to the site of injury also undergo some degeneration, occasionally involving the cell body but generally only affecting a few nodes of Ranvier. Wallerian degeneration stops all nerve conduction distal to the proximal axonal stump. This type of degeneration follows nerve transsection and other destructive processes that affect peripheral nerves and is likely to undergo spontaneous regeneration.
Regeneration of a peripheral nerve can begin almost immediately after nerve injury. Normally, the proximal nerve stump sends out a group of new fibers (axonal sprouts or the growth cone) that grow down the remnant Schwann cell tube. Growth progresses at a rate of 1 to 1.5 mm/day and continues until the site innervated by the nerve is reached or nerve regeneration is blocked by interposed fibrous connective tissue and nerve tissue (fibroma) or bone. During regeneration, new myelin sheaths may form as the axons increase in diameter. As functional contacts are made, the patient may experience altered sensations in the previously anesthetic area, which may take the form of paresthesias or dysesthesias.
Problems can occur during regeneration that prevent normal nerve healing. If the continuity of the Schwann cell tube is disrupted, connective tissue may enter the tube while it is partially vacant. When the growth cone (axonal sprouts) reaches the connective tissue obstruction, it may find a way around it and continue on, or it may form a mass of aimless nerve fibers that constitutes a traumatic neuroma subject to pain production when disturbed (trigger point).
(摘自Contemprorary oral and maxillofacial surgery, 7th ed.)