From the Guidelines
Acute disseminated encephalomyelitis (ADEM) imaging features typically include multiple, large, asymmetric white matter lesions on MRI that appear hyperintense on T2-weighted and FLAIR sequences, and spinal cord involvement is present in approximately 25% of cases of ADEM, with MRI of the spine being the reference standard for imaging of the spinal cord in cases of suspected demyelinating disease. The lesions in ADEM commonly affect the subcortical and deep white matter, cerebellum, brainstem, and spinal cord, with a tendency to involve both gray and white matter (particularly the thalamus and basal ganglia) 1. The lesions often demonstrate enhancement with gadolinium in the acute phase, indicating active inflammation and blood-brain barrier disruption, and diffusion-weighted imaging may show restricted diffusion in acute lesions 1. Unlike multiple sclerosis, ADEM lesions tend to appear simultaneously rather than in different stages, and they may partially or completely resolve on follow-up imaging, and CT scans are less sensitive but may show hypodense lesions in severe cases 1. These imaging characteristics, combined with clinical presentation of encephalopathy following a viral illness or vaccination, help distinguish ADEM from other demyelinating disorders, such as multiple sclerosis and neuromyelitis optica spectrum disorder (NMOSD) 1. Some key features to look for in ADEM include:
- Multiple, large, asymmetric white matter lesions on MRI
- Lesions that appear hyperintense on T2-weighted and FLAIR sequences
- Involvement of the subcortical and deep white matter, cerebellum, brainstem, and spinal cord
- Enhancement with gadolinium in the acute phase
- Restricted diffusion in acute lesions on diffusion-weighted imaging
- Resolution of lesions on follow-up imaging
- Clinical presentation of encephalopathy following a viral illness or vaccination.
From the Research
Adem Imaging Features
- Adem lesions are typically characterized by multiple demyelinating lesions in the white matter tracts of the cerebral hemispheres, brainstem, optic nerves, and spinal cord 2.
- Magnetic Resonance Imaging (MRI) is the definitive modality for assessing Adem lesions, with all patients showing abnormalities consistent with the clinical diagnosis 3.
- MRI findings in Adem include:
- High signal intensity on T2-weighted sequences, indicating patchy demyelinated lesions 4, 2.
- Restricted diffusion in the acute stage, with Apparent Diffusion Coefficient (ADC) values ranging from 0.37-0.68 x 10(-3) mm/s2 5.
- Free diffusion in the subacute stage, with ADC values ranging from 1.01-1.31 x 10(-3) mm/s2 5.
- Decreased NAA/Cho ratios in the subacute stage, indicating axonal damage or loss 5.
- Diffusion-weighted imaging (DWI) and proton magnetic resonance spectroscopy (MRS) can be used to characterize and stage Adem lesions, with significant differences in ADC values and MRS ratios between the acute and subacute stages 5.
- CT scans may be normal in some cases, highlighting the importance of MRI in diagnosing Adem 3.