Wallerian Degeneration
Overview
- Wallerian degeneration is a process where axons and myelin sheaths degenerate due to a proximal axonal or neuronal cell body insult.
- It occurs after neuronal loss due to:
- Cerebral infarction
- Trauma
- Necrosis
- Focal demyelination
- Hemorrhage
Pathology
- Wallerian degeneration is divided into four stages:
- Stage 1 (0-4 weeks):
- Degeneration of axons and myelin sheaths
- Mild chemical changes
- Stage 2 (4-14 weeks):
- Rapid destruction of myelin protein fragments
- Lipids remain intact
- Stage 3 (>14 weeks):
- Gliosis replaces degenerated axons and myelin sheaths
- Breakdown of myelin lipids
- Stage 4 (months to years):
- Atrophy of white matter tracts
Distribution
- Depends on the injury location and its relation to white matter tracts.
- Common pattern: Injury to precentral gyrus leading to degeneration of corticospinal tracts.
- Infarction of ventral pons can lead to bilateral middle cerebellar peduncle lesions due to degeneration of pontocerebellar fibers.
Radiographic Features
CT
- Less sensitive than MRI.
- Observed in chronic stages as a tract of gliosis from cortical/subcortical injury to deep structures.
MRI
- T1 MRI Stages:
- Stage 1: No changes
- Stage 2: T1 hyperintense
- Stage 3: T1 hypointense
- Stage 4: Brainstem atrophy (with or without hypointensity)
- T2 MRI Stages:
- Stage 1: No changes
- Stage 2: T2 hypointense
- Stage 3: T2 hyperintense
- Stage 4: Brainstem atrophy
- DWI: Shows high signal on DWI and low signal on ADC from initial days to 8 months post-insult.
History and Etymology
- Named after Augustis Volney Waller, who described the process in 1850.
References
- Various studies and articles are cited for further reading, offering insights into different aspects of Wallerian degeneration, including radiographic evaluations and diffusion changes.
These notes provide a concise summary of the key points related to Wallerian degeneration, focusing on pathology, distribution, radiographic features, and historical context.