Images of the month 1: Trident sign and neurosarcoidosis.

A 36-year-old woman presented with a subacute, relapsing myelitis, manifesting as bilateral ascending lower limb paraesthesia, partially responsive to steroids. Imaging demonstrated a longitudinal spinal cord lesion, with a unique and characteristic sign (the 'trident sign') on axial views, which is specific to a diagnosis of neurosarcoidosis. This case highlights the importance of using this feature to distinguish a longitudinal cord lesion of sarcoidosis from other differentials. © Royal College of Physicians 2021. All rights reserved.