Juxtacortical Paramagnetic Rim

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.