A probable case of peduncular hallucinosis secondary to a cerebral peduncular lesion successfully treated with an atypical antipsychotic.

Peduncular hallucinosis is a rare phenomenon that has been reported in case reports and case series. The exact pathophysiology is unclear, but is postulated to involve disruption and dysregulation of the visual neuronal pathways in the brain. A case of complex visual hallucinations in an elderly man with no previous history of psychosis is discussed. Magnetic resonance imaging of the patient's brain revealed a discrete peduncular lesion that was the likely cause of the hallucinations. The lesion was not present on a previous brain magnetic resonance imaging that predated the onset of the hallucinations. The patient was started on low-dose risperidone, which resulted in the complete resolution of the visual hallucinations. It is important to consider discrete rostral brainstem lesions as a potential cause of new onset visual hallucinations in patients being evaluated for visual hallucinations.