Brain MRI Findings in Infantile Spasms (West Syndrome)
The majority of infants with infantile spasms (84%) demonstrate structural abnormalities on brain MRI, with cortical dysplastic lesions being the most common finding, followed by hypoxic-ischemic injury, malformations of cortical development, and delayed myelination. 1, 2
Most Common MRI Abnormalities
Structural Abnormalities (Present in 84% of Cases)
Cortical dysplastic lesions represent the most frequently identified structural abnormality in infantile spasms, though these lesions may not be apparent on initial imaging until myelination has advanced sufficiently to allow visualization of poor gray-white matter differentiation 2. The pattern typically includes:
- Cortical gray and/or white matter abnormalities are present in both developmental and acquired subgroups of infantile spasms 3
- Malformations of cortical development are identified in approximately 9% of cases (5 out of 56 patients in one cohort) 1
Hypoxic-Ischemic Injury
Hypoxic injury is documented in 17% of brain MRIs in infantile spasms patients, representing a significant acquired etiology 1. This finding aligns with the broader pattern where acquired structural abnormalities account for approximately 44% of abnormal MRIs (23 out of 52 abnormal cases) 3.
Additional Structural Findings in Acquired Cases
In the acquired structural subgroup, MRI demonstrates more extensive abnormalities beyond cortical involvement 3:
- Deep gray structure abnormalities
- Brain stem involvement
- Corpus callosum abnormalities
- Volume loss/atrophy 3
Delayed Myelination
Delayed myelination is observed in 34% of infantile spasms patients (19 out of 56 cases), representing a common nonspecific finding that may indicate underlying developmental or metabolic abnormalities 1.
Normal MRI Findings
Only 16% of infants with infantile spasms have normal brain MRI, which represents the minority of cases and typically suggests cryptogenic etiology or lesions below the resolution of conventional MRI 1, 4.
Clinical Correlations and Prognostic Implications
Abnormal brain MRI findings strongly correlate with worse clinical outcomes, specifically:
- 64% of children with active epilepsy have abnormal brain MRI 1
- 82% of children with global developmental delay demonstrate abnormal brain MRI 1
- Abnormal findings on repeat MRI are significantly associated with both active epilepsy and developmental delay (p = 0.05) 1
Optimal Imaging Protocol
MRI brain is the highest yield initial diagnostic study for determining etiology in infantile spasms and should be performed using dedicated epilepsy protocols when available 4, 5. The ACR guidelines recommend:
- 3T scanners whenever possible for optimal resolution 5
- T1-weighted volumetric acquisition (3-D) with isotropic voxel size of 1 mm 5
- High-resolution thin coronal slices optimized for hippocampal pathology evaluation 5
Critical Timing Considerations
Repeat MRI may be necessary as cortical dysplastic lesions can become more apparent with advancing myelination, and follow-up imaging shows better definition of the extent of existing malformations 3, 2. Initial MRI performed too early in infancy may miss subtle cortical dysplasias that only become visible as gray-white matter differentiation improves with maturation 2.
Common Pitfalls to Avoid
- Do not rely on a single normal MRI to exclude structural etiology, as many cortical dysplastic lesions only become detectable with advancing myelination and may require repeat imaging 2
- Do not use CT imaging as the primary modality, as MRI has superior sensitivity (84%) compared to CT (62%) for detecting epileptogenic lesions 5
- Do not assume normal MRI indicates benign prognosis, as functional abnormalities detectable only by PET scanning may still be present in cases with normal structural imaging 2, 6