Axonotmesis
The axonotmesis is a traumatic injury of peripheral nerves with transection of the axon . The myelin sheath made of Schwann cells is also damaged, but it is crucial that the continuity of the nerve envelope structures ( endoneurium , perineurium , epineurium ) is preserved. Since the axon has been disrupted, Waller's degeneration initially takes place. The proximal axon stump forms a growth cone and grows out along the preserved endoneurial sheath. If the regeneration is successful, it is likely that the function will be largely restored.
Demarcation
Axonotmesis is a moderate form of nerve injury. In the division coined by Herbert Seddon , it is differentiated from the lighter neurapraxia and the even more severe neurotmesis
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Scheme of an intact nerve | |
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Neurapraxia | Axon and envelope tissue are preserved. |
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Axonotmesis | The axon is severed, but the covering tissue is preserved. |
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Neurotmesis | Complete severing of the nerve and its envelope structures |
Examination Findings
Neurographically , the excitability of the nerve is lost distal to the lesion site, paresis , muscle atrophy and sensory disturbances occur in the innervation area of the nerve , and vegetative functions are also impaired.
forecast
In axonotmesis, in contrast to neurapraxia, the axon degenerates beyond the point of damage. The prognosis is nevertheless favorable, as the continuity of the surrounding connective tissue and the basement membrane is preserved. Therefore, extensive or even complete regeneration of the nerve function can occur. The sprouting of a new axon takes place at a rate of 0.25 to 3 mm per day. The restitution therefore takes considerably longer than with a pure neurapraxia - depending on the length of the damaged nerve segment in the order of weeks to months. The ability to regenerate remains for years.
literature
- Marco Mumenthaler , Manfred Stöhr, Hermann Müller-Vahl: Lesions of peripheral nerves and radicular syndromes. 8th edition. Thieme Stuttgart, 2003. ISBN 3-13-380208-9 .