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Updated: Jul 6, 2025
Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla
Published on: February 19, 2021
Juxtacortical Paramagnetic Rim: A New MRI Marker to Characterize Focal Cortical Pathology in Multiple Sclerosis?
Maria A Rocca1, Paolo Preziosa1, Massimo Filippi1
1From the Neuroimaging Research Unit (M.A.R., P.P., M.F.), Division of Neuroscience; Neurology Unit (M.A.R., P.P., M.F.), IRCCS San Raffaele Scientific Institute; Vita-Salute San Raffaele University (M.A.R., P.P., M.F.); Neurorehabilitation Unit (M.F.); and Neurophysiology Service (M.F.), IRCCS San Raffaele Scientific Institute, Milan, Italy.
Abstract:
The accumulation of focal white matter and cortical inflammatory demyelinating lesions represents the pathologic hallmark of multiple sclerosis (MS).1 Typically, acute white matter lesions are characterized by an increased blood-brain barrier (BBB) permeability, an inflammatory infiltrate, and ongoing demyelination and axonal transection.2 In the chronic phase, a substantial proportion of white matter lesions, known as chronic active lesions, exhibit a hypocellular core with a rim of iron-laden activated microglia/macrophages, with no abnormal BBB permeability.2 Some of these lesions can be identified on susceptibility-based MRI as exhibiting a paramagnetic rim, and they are, therefore, referred to as "paramagnetic rim lesions" (PRLs).3.
Insights
The hallmark of multiple sclerosis (MS) is inflammatory demyelinating lesions in the brain. Chronic active lesions, identified as paramagnetic rim lesions (PRLs) on MRI, show a unique cellular structure and iron deposition.
Area of Science:
- Neuroimmunology
- Neuroinflammation
- Demyelinating diseases
Background:
- Multiple sclerosis (MS) is characterized by focal white matter and cortical inflammatory demyelinating lesions.
- Acute lesions show blood-brain barrier (BBB) breakdown, inflammation, demyelination, and axonal damage.
- Chronic active lesions feature a hypocellular core with an iron-laden microglia/macrophage rim and intact BBB.
Discussion:
- Paramagnetic rim lesions (PRLs) are a subset of chronic active lesions identifiable via susceptibility-based MRI.
- The paramagnetic rim signifies iron deposition within activated microglia/macrophages at the lesion border.
- PRLs represent a specific stage of MS lesion evolution with distinct pathological features.
Key Insights:
- PRLs are a pathological hallmark of multiple sclerosis, indicating chronic inflammatory activity.
- The presence of a paramagnetic rim on MRI is a direct indicator of iron-laden microglia/macrophages.
- Understanding PRLs aids in differentiating lesion activity and chronicity in MS patients.
Outlook:
- Further research into PRLs may refine diagnostic criteria and prognostic indicators in MS.
- Investigating the role of iron metabolism in MS pathogenesis could reveal new therapeutic targets.
- Advanced MRI techniques focusing on paramagnetic rim detection may improve monitoring of disease progression.
