Barbell sign (progressive multifocal leukoencephalopathy)

Last revised by Lachlan McKay on 19 Mar 2024

The barbell sign is a radiological sign present in progressive multifocal leukoencephalopathy (PML) on MRI brain.

This describes confluent T2/FLAIR parieto-occipital abnormalities with a thin continuation of signal abnormality across the splenium 1,2. Given the lack of mass effect typically exhibited in PML this appears as a thin band between the abnormal regions, similar to a barbell/dumbbell 1. This should be discriminated from the enlargement of the splenium in other inflammatory or neoplastic processes.

Case series have found this sign in immunocompromised patients (both HIV and non-HIV associated), all with visual disturbance 1.

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