Acute flaccid myelitis (AFM) presents with acute onset of flaccid paralysis with involvement of the gray matter on magnetic resonance imaging (MRI) of the spinal cord. Studies have reported brain MRI abnormalities, but the characteristics have not been fully defined. In this multicenter study, we assessed the acute features and evolution of brain MRI abnormalities in AFM.

We reviewed brain MRIs of patients with AFM who presented to four referral hospitals between 2012 and 2018. Cases met established criteria for AFM. We analyzed the initial and follow-up brain MRIs. Areas were divided into supratentorial, infratentorial, and subdivisions within those regions.

A total of 66 patients were included. Brain MRI abnormalities were present in 34 (52%). Infratentorial abnormalities were more common, occurring in 33 (97%) cases with the dorsal pons being the most frequently affected area (88%). Abnormalities were also present in the medulla (74%), cerebellum (41%), and midbrain (38%). Nine subjects (26%) exhibited both supratentorial and infratentorial abnormalities, whereas isolated supratentorial changes were present in only one (3%). Contrast-enhancing abnormalities were encountered in 9% of cases and meningeal involvement in 6%. On follow-up, most abnormalities, 20 of 24 (83%), were stable, improving, or had resolved.

Brain MRI abnormalities occur in about half of the cases of AFM and commonly resolve with time. Dorsal pontine involvement is a characteristic MRI feature, whereas isolated supratentorial abnormalities are rare. Clinicians should consider that brain imaging abnormalities do not exclude a diagnosis of AFM in patients with typical presentations.