The concentric onion ring pattern of these lesions is characteristic of Balo concentric sclerosis. This is a variant of demyelination with the alternating intralesional intensities representing myelinated and demyelinated axons 1. The regions of true diffusion restriction reflect active demyelination. Over time, the onion ring plaques coalesce to form more homogeneous T2 hyperintense plaques.
Although typically described in young adults, pediatric cases are not uncommon 2.