Brain MRI Findings Suggesting MS vs CNS Lymphoma in a Young Adult Initially Suspected of Ventriculitis
Key Distinguishing MRI Patterns
The radiologist likely observed periventricular white matter lesions with variable enhancement patterns that could fit either MS or CNS lymphoma, prompting further workup to distinguish between these inflammatory/demyelinating versus neoplastic processes. 1
Specific MRI Features That Raised MS Suspicion
Lesion Distribution Characteristics
- Periventricular lesions perpendicular to the corpus callosum ("Dawson's fingers") are highly characteristic of MS and would be a primary feature suggesting this diagnosis 1, 2
- Juxtacortical lesions involving U-fibers in direct contact with cortex without intervening white matter 1
- Infratentorial lesions in the brainstem or cerebellum 2
- Multiple focal, well-demarcated lesions with sharp edges, typically <3 cm, round or flame-shaped 2
Enhancement Patterns Favoring MS
- Nodular enhancement or open-ring enhancement (opening toward ventricles or cortex) are typical MS patterns 1
- Enhancement typically lasts 2-8 weeks, occasionally up to 3 months, but persistent enhancement beyond 3 months suggests alternative pathology 1, 3
- Simultaneous presence of both enhancing and non-enhancing lesions demonstrates dissemination in time 1, 4
Specific MRI Features That Raised CNS Lymphoma Suspicion
Atypical Features for MS ("Red Flags")
- Large closed-ring enhancing lesions with significant mass effect are atypical for MS and suggest neoplasm 1
- Persistent gadolinium enhancement >3 months strongly suggests malignancy rather than demyelination 1, 3
- Periventricular location with mass effect and surrounding edema 5, 6
- Lesions involving deep gray matter structures (basal ganglia) are uncommon in MS but can occur in CNS lymphoma 6
CNS Lymphoma-Specific Patterns
- Homogeneous or inhomogeneous enhancement of large (>2 cm) tumefactive lesions 1
- Diffuse, poorly marginated lesions rather than the discrete, well-demarcated lesions typical of MS 6, 7
- Lesions may show low uptake on PET imaging, which can paradoxically mimic demyelination 6
- Nonenhancing lesions can rarely occur in CNS lymphoma, particularly if corticosteroids were administered, which can mask typical enhancement patterns 5, 6
Why Ventriculitis Was Initially Considered
Overlapping Features
- Periventricular location of lesions adjacent to ventricles could suggest ependymal inflammation 1
- Enhancement patterns near ventricular surfaces might initially suggest infectious/inflammatory ventriculitis
- However, extensive leptomeningeal enhancement would be expected in true ventriculitis but is extremely rare in MS 1
Critical Diagnostic Workup Required
Essential Next Steps
- Brain biopsy is often necessary when imaging cannot definitively distinguish between MS and CNS lymphoma, particularly with atypical features 5, 6
- CSF analysis showing oligoclonal bands (present in >95% of MS) versus elevated protein and atypical cells (suggesting lymphoma) 2
- Spinal cord MRI to identify additional short-segment peripheral lesions typical of MS 1, 2, 4
- Follow-up MRI at 3-6 months to assess lesion evolution—MS lesions typically show new lesions with variable enhancement, while lymphoma shows progressive growth 7
Common Diagnostic Pitfalls
- Corticosteroid administration can mask typical enhancement patterns in CNS lymphoma, making it appear more like demyelination 5, 6
- Tumefactive MS lesions can mimic lymphoma with large size and mass effect, but typically show open-ring enhancement pattern 1
- Overdiagnosis of MS occurs when non-specific T2 hyperintensities are misinterpreted—only 35.4% of suspected RIS cases actually fulfill McDonald criteria 7
- Concurrent occurrence of MS and CNS lymphoma, though rare, has been documented and requires high clinical suspicion when atypical features develop 5, 8