MRI Pattern of X-linked Adrenoleukodystrophy
The characteristic MRI pattern of X-linked adrenoleukodystrophy (X-ALD) shows symmetric, butterfly-shaped T2 hyperintensity and T1 hypointensity in the parieto-occipital white matter, with involvement of the splenium of the corpus callosum causing bilateral lesions to converge, and thin lacelike contrast enhancement at the advancing edge of demyelination. 1, 2
Classic Parieto-Occipital Pattern (Pattern 1)
The most common presentation involves the posterior white matter with specific features:
- Symmetric butterfly-shaped lesions in the parieto-occipital white matter appearing as low T1 and high T2 signals 1
- Splenium of corpus callosum involvement that causes bilateral lesion regions to converge into one continuous area 1
- Anterior progression that can extend to injure the bilateral posterior limb of internal capsule and temporal lobes 1
- Inferior extension that may involve the brainstem 1
- Thin stripe of lacelike enhancement visible after intravenous contrast administration at the leading edge of demyelination 1, 3
This pattern occurs mainly in childhood and demonstrates rapid progression, especially when contrast enhancement is present and when MRI abnormalities manifest at an early age 2.
Alternative Anatomic Patterns
X-ALD can present with five distinct MRI patterns based on initial lesion location:
- Pattern 2 (Frontal white matter): Occurs mainly in adolescence with rapid progression when manifesting at early age 2
- Pattern 3 (Corticospinal tract): Occurs predominantly in adults with much slower MRI progression 2
- Pattern 4 (Cerebellar white matter): Presents in adolescence with slower progression; atypical initial symptom may be seizures 1, 2
- Pattern 5 (Concomitant parieto-occipital and frontal): Rare pattern occurring mainly in childhood with more rapid progression than any other pattern 2
Atypical Presentations
Asymmetric lesions can occur in initial presentation despite the typical symmetric pattern, with predominance in one hemisphere that may later evolve to appear approximately symmetric as disease progresses 4. Isolated bilateral temporal white matter lesions involving corticospinal tracts with sparing of parieto-occipital and frontal white matter represent another atypical temporal pattern 5.
Critical Prognostic Features
Contrast enhancement on T1-weighted images is the single most important predictor of disease progression. Among patients with enhancement on initial MRI, 86% demonstrate disease progression on follow-up, while 82% of patients without enhancement show no progression 3. This finding is critical for selecting candidates for bone marrow transplantation.
The combination of three variables predicts disease course most accurately:
- Patient age at presentation 2
- Initial MRI Severity Scale score (34-point scale based on anatomic extent) 2
- Anatomic location/pattern of the lesion 2
Key Distinguishing Characteristics
The hallmark feature differentiating X-ALD from other leukoencephalopathies is the prominence of gray matter sparing with selective white matter involvement on conventional MRI sequences 6. The symmetric butterfly configuration with corpus callosum involvement and characteristic contrast enhancement pattern at the advancing edge distinguishes X-ALD from conditions like CSF1R-related leukoencephalopathy, which shows patchy or confluent white matter lesions predominantly in frontoparietal regions without this specific geometric pattern 6.