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MRI findings in multiple sclerosis

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"multiple sclerosis"[MeSH Terms] AND "magnetic resonance imaging"[MeSH Terms]

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MRI Findings in Multiple Sclerosis

MRI is the single most important paraclinical tool for diagnosing and monitoring MS. More than 95% of patients with clinically definite MS have an abnormal brain MRI; a normal brain MRI should prompt consideration of an alternative diagnosis.

1. Lesion Characteristics - General

MS plaques appear as T2-hyperintense (bright) lesions on fluid-attenuated inversion recovery (FLAIR) sequences, which suppress CSF signal from the ventricles and optimise detection of supratentorial lesions. Key features of individual lesions:
  • Size: typically 2 mm - 2 cm; rarely, large lesions can mimic a tumour
  • Shape: elliptical with discrete borders
  • Mass effect: absent (helps distinguish from tumour/abscess)
  • Margins: well-defined in chronic plaques; less well-defined in acute lesions

2. Lesion Distribution - DIS (Dissemination in Space)

The 2017 McDonald criteria require T2 lesions in at least 2 of 4 CNS regions to demonstrate dissemination in space:
RegionDetails
PeriventricularPerpendicular to lateral ventricle walls - "Dawson's fingers" on sagittal FLAIR
Cortical / juxtacorticalAt the grey-white junction; FLAIR is superior to T2 for detection
InfratentorialCerebellum, cerebellar peduncles, brainstem (outer margin of pons)
Spinal cordDorsolateral columns; "cigar-shaped" <2 vertebral segments; rarely >half cord cross-section
The calloso-septal interface (inferior margin of the corpus callosum) is a classic location, well seen on sagittal FLAIR.
Fig. 58.5 - Early RRMS: Calloso-septal interface lesions (sagittal T2-FLAIR)
Early RRMS: Sagittal T2-FLAIR shows typical MS lesions on the calloso-septal interface.

3. Dawson's Fingers

On sagittal FLAIR, periventricular lesions orient perpendicularly outward from the ventricles along perivascular spaces - producing the classic "Dawson's fingers" sign. This orientation reflects the perivenular distribution of MS plaques.
Typical MS brain lesions: axial PV + juxtacortical (A), sagittal Dawson's fingers (B), infratentorial (C)
A: Axial view - periventricular (PV) and juxtacortical lesions. B: Sagittal - classic Dawson's finger appearance. C: Axial - posterior fossa lesions.
Axial FLAIR - periventricular and deep white matter lesions
Axial FLAIR: Multiple periventricular and deep white matter high-signal lesions.
Sagittal FLAIR - periventricular lesions radiating from ventricles
Sagittal FLAIR: Classic periventricular lesions radiating outward from the ventricles (arrows).

4. Juxtacortical Lesions

Lesions at the grey-white junction (juxtacortical) are best seen on FLAIR compared with standard T2. They are one of the four DIS regions in the McDonald criteria. Double inversion recovery (DIR) sequences offer the highest sensitivity for detecting purely cortical lesions.
Juxtacortical lesion better seen on FLAIR vs T2
A (T2): Juxtacortical lesion inferior frontal lobe. B (FLAIR): Same lesion better depicted (arrow).
DIR showing two cortical lesions (arrows)
Double inversion recovery (DIR): Two cortical lesions in a CIS patient (arrows).

5. Gadolinium Enhancement - Active / Acute Lesions

Gadolinium enhancement indicates blood-brain barrier disruption due to acute perivascular inflammation. It detects disease activity 5-10 times more frequently than clinical relapse assessment alone.
Key facts about enhancement in MS:
  • Duration: typically days to weeks (median ~3 weeks; rarely beyond 2-3 months)
  • Pattern: nodular, homogeneous, or ring-type; may evolve from nodular to ring
  • Open (incomplete) ring enhancement is a useful sign - the open side faces grey matter/cortex, unlike the closed rings of abscess or high-grade tumour
  • Enhancement is rapidly suppressed by steroids
  • Less frequent in spinal cord vs. brain (4-10x more common in brain)
  • Even clinically stable patients can have enhancing lesions (subclinical activity)
Axial T1+Gd - ring-enhancing active MS lesion
T1-weighted post-gadolinium: Actively inflamed ring-enhancing lesion (arrow) in MS.

6. T1 "Black Holes"

Persistent areas of T1 hypointensity (dark on pre-contrast T1) are called "black holes." They correlate with irreversible axonal loss and atrophy - the neurodegenerative component of MS. They are a marker of poor prognosis and are monitored in disease-modifying therapy (DMT) decisions. Acute T1 lesions can also appear (reflecting edema/demyelination) but may resolve; persistent T1 hypointensity implies permanent tissue destruction.

7. Spinal Cord MRI

  • Detected in up to 90% of MS patients, often asymptomatic
  • Cervical > thoracic > lumbar in frequency
  • Sagittal appearance: "cigar-shaped," spanning <2 vertebral segments
  • Cross-sectional: lateral and posterior white matter columns; rarely anterior columns or central grey matter; rarely >50% cord cross-section
  • These cord features help differentiate MS from NMOSD (which causes longer, central cord lesions >3 segments)
Sagittal T2 of brain and cervical spine in MS
Sagittal T2: Brain and cervical spine - MS lesions visible.

8. Dissemination in Time (DIT) on MRI

DIT can be demonstrated by:
  1. Simultaneous presence of a gadolinium-enhancing lesion AND a non-enhancing T2 lesion on a single scan (they represent lesions of different ages)
  2. New T2 or gadolinium-enhancing lesion on a follow-up scan compared with baseline, regardless of the interval between scans

9. Brain Atrophy

Brain volume loss is the most robust MRI biomarker of neurodegeneration in MS. Atrophy occurs from early in the disease course, even in clinically isolated syndrome, and progresses across all phenotypes. It parallels disability accumulation better than T2 lesion load alone in progressive MS.

10. Advanced / Quantitative MRI Techniques

TechniqueWhat It Measures
Magnetisation transfer ratio (MTR)Myelin content / demyelination in NAWM
Diffusion tensor imaging (DTI)Axonal integrity, tract disruption
Proton MR spectroscopyNAA (axonal marker), choline, lactate
Susceptibility-weighted imaging (SWI)Iron rims around chronic active lesions ("rim signs")
Optical coherence tomography (OCT)Retinal nerve fibre layer - surrogate for optic nerve/CNS damage
These are used in research but not yet routine clinical practice for treatment monitoring.

11. Primary Progressive MS (PPMS) on MRI

PPMS typically shows:
  • Smaller T2 lesion load and less gadolinium enhancement than relapsing MS
  • More prominent spinal cord involvement
  • Greater cortical damage and diffuse normal-appearing white matter (NAWM) damage
  • This "MRI-clinical paradox" (modest MRI lesion load but significant disability) is partly explained by extensive cortical and spinal cord pathology

McDonald Criteria 2017 Summary (MRI-based)

DIS = ≥1 T2 lesion in ≥2 of: periventricular, cortical/juxtacortical, infratentorial, spinal cord
DIT = Simultaneous enhancing + non-enhancing lesions at any time point, OR new T2/Gd+ lesion on follow-up
Sources:
Recent systematic reviews confirm the current DIS/DIT framework remains highly accurate for distinguishing MS from NMOSD and MOGAD based on lesion distribution (PMID: 40889881, 40773034).
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