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Multiple Sclerosis: Typical, Changing, or a Red Flag?

Fellowship-level neuroradiology teaching by E. Brooke Schrickel, MD. Open this topic in the interactive reading room →

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Core clinical idea

Not all white-matter disease is MS, and the MS read isn't 'are there lesions' but 'are they MS-typical, are they changing, and is anything here that demands I abandon the MS label or warn the clinician.' Confirm an MS-typical disseminated pattern, then run a disciplined follow-up that catches subclinical change and treatment complications — and reopen the differential if it progresses on therapy.

Bottom line

Confirm the MS pattern, then count what changed and watch the volume — but if it progresses on therapy or looks atypical, stop anchoring and call the mimic.

Core workstation questions

  • Is the distribution MS-typical (perpendicular/Dawson's fingers, juxtacortical, infratentorial, short peripheral cord lesions), with a central vein sign on SWI?
  • How many new or enlarging lesions vs prior, and does that delta cross a therapy-change threshold?
  • Is there interval global brain volume loss (watch the Sylvian fissures)?
  • Is there a new ring-enhancing/diffusion-restricting lesion that could be PML, infection, or abscess on therapy?
  • Is the patient progressing despite disease-modifying therapy or imaging/clinically atypical — should I recommend AQP4/MOG testing or call a mimic?
  • Does the lesion show a central vein or an iron (paramagnetic) rim on SWI?
  • Is the optic nerve involved (now a qualifying DIS site under 2024 McDonald)?

What changes reporting / management

  • Contrast is often unnecessary to flag activity — a lesion that restricts diffusion and enhances is active; DWI can identify active demyelination without gadolinium in patients facing decades of serial scans.
  • Treat the lesion-burden comparison as a treatment decision — even two or three new lesions can prompt a therapy change; finish the search pattern.
  • Comment on global brain volume every follow-up; parenchymal volume loss tracks with disability and cognitive decline.
  • Suggested phrasing when atypical: lesions atypical for MS and progression despite disease-modifying therapy; recommend correlation with aquaporin-4 and MOG antibody testing to exclude an MS mimic.
  • 2024 McDonald criteria: the optic nerve is now a 5th CNS topography for dissemination in space (orbital MRI / VEP / OCT) — say so when an optic nerve lesion is the qualifying site.
  • Look on SWI for the central vein sign (a vein running through the long axis of the ovoid lesion = perivenular demyelination) and paramagnetic 'iron' rim lesions (hypointense rim of iron-laden microglia at a chronic active lesion) — both add specificity for MS over mimics.

Practical traps

  • Anchoring on MS when the patient worsens on therapy or the picture is atypical — the single biggest error; reopen the differential (NMOSD, MOG, ADEM, PML, vasculitis, Susac).
  • Treating a new ring-enhancing, diffusion-restricting lesion in a treated MS patient as automatically a tumefactive plaque when abscess or PML are on the table.
  • Missing short-segment peripheral cord lesions on sagittal images — use high-resolution axial T2.
  • Letting 'known MS' shrink the search pattern and missing new disease (e.g., cauda equina nerve-root enhancement / CIDP-type process).

Teaching pearls

  • Not all white-matter disease is MS — progression despite therapy means reopen the differential.
  • You usually don't need gadolinium: a lesion that restricts and enhances is active.
  • Two or three new lesions can change therapy — finish the search and count carefully.
  • Comment on brain volume every follow-up; atrophy tracks disability.
  • A new ring-enhancing, restricting lesion on MS therapy may be PML or abscess, not a plaque.
  • Central callosal 'snowball' lesion plus hearing loss and retinal occlusions = Susac, not MS.
  • Central vein sign on SWI = perivenular demyelination — supports MS over mimics (e.g., migraine, small-vessel disease).
  • Paramagnetic rim / iron-rim lesion = chronic active lesion; fairly specific for MS and tracks with disability.
  • 2024 McDonald: optic nerve as a 5th DIS site; central vein sign, paramagnetic rim lesions, and CSF kappa free light chains can be used as supportive specificity markers.

Teaching visuals

Multiple sclerosis — 2024 McDonald + the lesion mapMRI-inspired axial schematic of the characteristic dissemination-in-space topography (teaching aid).Axial schematic — MS lesion topographyegg-shaped brain · lateral ventriclesPeriventricular (Dawson fingers) — ovoids ⟂ to ventriclesJuxtacortical / cortical — ovoids touching the cortexDissemination in space — ≥2 of 5 CNS sites1Periventricularshown above2Cortical / juxtacorticalshown above3Infratentoriallegend only4Spinal cordlegend only5Optic nerve — NEW 2024legend onlyCentral vein signperivenular demyelination (SWI)vein through the lesion long axisParamagnetic rim lesionchronic-active “iron rim” (SWI)iron-laden microglia at the edge2024 McDonald — supportive biomarkersOptic nerve = 5th DIS siteadded as a 5th CNS topographyCentral vein signvein through an ovoid’s long axisParamagnetic rim lesionschronic-active lesion, iron rim on SWICSF kappa free light chainssupportive specificity biomarker
Multiple Sclerosis — 2024 McDonald & SWI Signs

Source lectures

  • Multiple Sclerosis

Educational material for radiology residents and neuroradiology fellows. Nothing here drives individual patient care, and it contains no patient data.