Multiple Sclerosis, active demyelination with positive DWI but no enhancement
Findings:
Multiple MR images demonstrate extensive ovoid periventricular white matter lesions compatible with demyelination. Ovoid lesions in the left thalamus and right centrum semiovale demonstrate restricted diffusion and no abnormal enhancement.
Differential Diagnosis:
Active MS, acute infarcts, neoplasm
Discussion:
In my experience, it is far more common to see active enhancing demyelinating lesions that do not restrict diffusion than active nonenhancing lesions that do restrict diffusion. However, the overall morphology of the other lesions is highly compatible with demyelinating process. The lack of mass effect or expansile appearance makes superimposed neoplasm unlikely, and the morphology is also atypical for ischemic infarction. Further discussion of multiple sclerosis is found in other cases on this site.