ADEM

In clinically defined cases of ADEM, the MRI will often demonstrate multifocal areas of increased T2-weighted (T2W) signal abnormalities in the CNS white matter, with or without gray matter involvement. Some authors have proposed that ADEM lesions are indistinct and lack sharply defined borders ("fluffy and diffuse") characteristic of MS lesions.  Although ADEM lesions (of similar age) should all hypothetically enhance with gadolinium, this finding is rarely seen, and gadolinium enhancement may even be absent.

Early MRI series identified overlap in lesion location and distribution between ADEM and MS, but also highlighted features of ADEM that are unusual in MS, such as symmetric bilateral disease, relative sparing of the periventricular white matter, or deep gray matter involvement.64 Absolute and relative periventricular sparing on MRI is typical of ADEM, and was present in 78% of patients with ADEM. However, 22% of ADEM patients had a periventricular lesion pattern indistinguishable from that seen in MS, and the characteristic corpus callosum long axis lesions (Dawson’s fingers), together with the finding of only well-defined lesions, were completely specific indicators of relapse/progression to MS.