T2/Fluid Attenuation Inversion Recovery Hypointensity of Corticospinal Tracts due to Subacute Stage of Wallerian Degeneration.

A 67-year-old male, with a history of sudden onset of left-sided weakness 4 weeks back, came to our hospital for neurorehabilitation. His magnetic resonance imaging (MRI) revealed chronic infarct in the right insula, inferior frontal gyrus, lateral thalamus, and gangliocapsular region. T2/fluid attenuation inversion recovery (FLAIR) hypointensity was noted along the right corticospinal tract in brainstem, with mild brainstem atrophy [Figure 1, arrows].

Figure 1

(a and b) Axial fluid attenuation inversion recovery and T2-weighted magnetic resonance images showing subacute infarct in the right gangliocapsular region, chronic infarct in the right frontal lobe and insula. (c-j) Serial axial sections of brain showing T2 and fluid attenuation inversion recovery hypointensity of corticospinal tracts in brainstem (arrows)

Wallerian degeneration of corticospinal tracts after acute infarct progresses through three stages, which can be detected earlier and better appreciated by diffusion tractography imaging (DTI),[12] though advanced stages can be detected by conventional imaging as well. The first stage consists of no signal change in conventional MRI lasting for 4 weeks, the second stage consists of T2/FLAIR hypointensity lasting for 4–10 weeks, and the third stage consists of T2/FLAIR hyperintensity of tracts 10–12 weeks onward. While conventional imaging detects advanced stage of T2/FLAIR hyperintensity with volume loss, detection of early and subacute stages is frequently not reported. The subacute stage of T2/FLAIR hypointensity is attributed to alteration in protein–lipid–water content of myelin as a result of degradation and disintegration of myelin sheath. The T2/FLAIR hypointensity of corticospinal tracts during Wallerian degeneration was initially demonstrated by Kuhn et al.,[3] though the subsequent study did not demonstrate such phenomenon out of 150 patients.[4] Identification of corticospinal tract signal intensity changes and DTI abnormalities during Wallerian degeneration is strongly and significantly predictive of motor outcome of patients.[5]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.