Specific Imaging Findings

CT is usually normal unless lesions are large, when they appear as subtle hypodensities. On MRI, lesions of acute disseminated encephalomyelitis (ADEM) are typically multiple and asymmetrically distributed, usually involving cerebral white matter and deep gray matter nuclei. Cortical gray matter and infratentorial involvement is also common. The lesions are T2 hyperintense and iso- to faintly hypointense on T1-weighted images, usually with little mass effect. Periventricular MS-like lesions and “black holes” on T1-weighted images are unusual. Contrast enhancement is uncommon and can have variable appearances. Diffusion findings vary, in part depending upon the stage of disease, with reduced diffusion more commonly observed in the acute stage. PWI shows reduced or normal rCBV within lesions. MRS will show lactate and normal or reduced levels of NAA in the acute stage, and reduced NAA and increased choline in the subacute stage. Approximately 30% of patients with ADEM will also have spinal cord involvement on MRI, usually extending over multiple levels with frequent enlargement of the brainstem and spinal cord.

Pertinent Clinical Information

ADEM is a monophasic disorder which typically begins within days to weeks after a prior infectious episode or vaccination. Although the syndrome can occur at any age, it is more common in children. Patients present with rapid onset encephalopathy which may be preceded by a prodromal phase of fever, malaise, headache, nausea, and vomiting. Neurologic symptoms of ADEM include unilateral or bilateral pyramidal signs, acute hemiplegia, ataxia, cranial nerve palsies, visual loss due to optic neuritis, seizures, impaired speech, paresthesias, signs of spinal cord involvement, and alterations in mental status, ranging from lethargy to coma.