Visualization of hypermetabolism in the ventral visual pathway by FDG-PET in the Charles Bonnet syndrome

A 74-year-old man presented with complex visual hallucinations with a left inferior quadrantanopia. The characteristics of the visual hallucinations met the criteria for the Charles Bonnet syndrome. Brain magnetic resonance imaging (MRI) revealed a right occipital falx meningioma. Fusion images of gadolinium-enhanced MRI and ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) of the brain demonstrated hypometabolism in the right primary and secondary visual cortices, and an ipsilateral hypermetabolism in a focal area of the medial aspect of the secondary visual cortex as well as the lateral part of the ventral visual pathway. These findings imply that hyperactivation of the ventral visual pathway, especially the lateral aspect of the ventral occipitotemporal cortex, may be related to the face hallucinations in this patient. This case highlights features of FDG-PET that can explain the pathophysiology of the Charles Bonnet syndrome.