Barbell sign (progressive multifocal leukoencephalopathy)
The barbell sign has been described in a short series of patients with progressive multifocal leukoencephalopathy (PML) 1.
This describes confluent FLAIR / T2w parieto-occipital abnormalities with a thin continuation of signal abnormality across the splenium.
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. 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.