wallerian degeneration
Wallerian degeneration is the process of antegrade degeneration of the axons and their accompanying myelin sheaths following proximal axonal or neuronal cell body lesions. It may result following neuronal loss due to cerebral infarction, trauma, necrosis, focal demyelination, or hemorrhage.
In cases of cerebral infarction, Wallerian degeneration appears in the chronic phase (>30 days).
Pathology
Classification
It is usually classified into four stages:
- stage 1: degeneration of the axons and myelin sheaths with mild chemical changes (0-4 weeks)
- stage 2: rapid destruction of myelin protein fragments that were already degenerated, lipids remain intact (4-14 weeks)
- stage 3: gliosis replaces the degenerated axons and myelin sheaths, myelin lipid breakdown (>14 weeks)
- stage 4: atrophy of the white matter tracts (months to years)
Distribution
The distribution of Wallerian degeneration depends on the region of injury and how it relates to white matter tracts that originate there. The most commonly observed pattern is an injury to the precentral gyrus (such as may be seen in an MCA infarct) with resultant degeneration of the corticospinal tracts.
In the cord, Wallerian degeneration can occur both rostrally (involving the dorsal columns above the injury) and caudally (involving the lateral corticospinal tracts below the injury) .
Radiographic features
CT
CT is not as sensitive as MRI, and Wallerian degeneration is generally observed only in its chronic stage. It is seen as a contiguous tract of gliosis leading from a region of cortical or subcortical neuronal injury towards the deep cerebral structures, along the expected topographical course of the involved white matter tract.
MRI
Corresponding stages have been described on MRI.
- T1
- no changes
- T1 hyperintense
- T1 hypointense
- brainstem atrophy with or without hypointensity
- T2
- no changes
- T2 hypointense
- T2 hyperintense
- brainstem atrophy
DWI
High signal on DWI and low signal on ADC have been demonstrated along the affected white matter tracts, from the first days after insult until 8 months after .
History and etymology
It is named after the English neurophysiologist Augustis Volney Waller (1816-1870), who described the process in 1850 .
Siehe auch:
- Diffuses axonales Schädelhirntrauma
- Seddon's classification
- peripheral nerve injury
- digestion chambers nerve injury
- Axonotmesis
- primary and secondary brain injury
- Neuroregeneration
- connective tissue in the peripheral nervous system
und weiter:
Assoziationen und Differentialdiagnosen zu Wallersche Degeneration: