The Monocle Sign in FDG-PET: A Sign of Contralateral Facial Nerve Palsy

We report three cases of unilateral F-FDG uptake in the orbicularis oculi muscle in subjects with contralateral peripheral facial nerve palsy. We argue that this asymmetric uptake pattern in fact reflects lack of metabolism on the side affected by facial nerve palsy, owing to denervation. Since the unilateral periorbital uptake resembles a monocle, we chose to call this finding the monocle sign. The monocle sign should not be confused with inflammation or tumor, but should prompt a neurological assessment for facial nerve palsy and a potential underlying disease.