Restricted diffusion preceding gadolinium enhancement in large or tumefactive demyelinating lesions.

Although restricted diffusion without coincident contrast enhancement is most commonly associated with cerebral ischemia, large or tumefactive multiple sclerosis (MS) lesions may demonstrate this pattern initially, followed by subsequent gadolinium (Gd) enhancement. The clinical and MRI characteristics of 3 patients with MS with this imaging pattern are reviewed. All patients had brain MRI lesions >1 cm in diameter, in locations consistent with new neurologic symptoms, and with prominent restricted diffusion but no Gd enhancement. Demyelinating lesion etiologies were supported by CSF findings, laboratory exclusion of alternative diagnoses, lesion evolution, or additional lesions characteristic of MS on brain MRI. Follow-up imaging within 2-4 weeks showed decreased restricted diffusion with patchy Gd enhancement which resolved on subsequent imaging. This imaging evolution may reflect early demyelination prior to inflammation-associated blood-brain barrier disruption.