Background: Visual hallucinations are disturbances of perception present in various pathologies. Peduncular hallucinosis is complex visual hallucinations involving animals or often terrifying people that occur after pontine injuries. In this case report we present the clinical history of a middle-age man who reported peduncular hallucinosis due to mild but numerous ischemic lesions in the pontine region. This is a peculiar condition as the literature reports PH for much more severe injuries.

Case presentation: A 55-year-old Caucasian man with hypertension, dyslipidemia, carotid atheromatosis and a previous diagnosis of bipolar disorder was admitted to the psychiatry ward of the Sant'Andrea Hospital due to the appearance of a mixed mood state with psychomotor agitation, ideic acceleration, anguish, auditory hallucinations, severe anxiety, panic attacks, total insomnia, disturbances in concentration and suicidal ideation. During hospitalization, he had complex visual hallucinations. On MRI of the brain, there were numerous ischemic areas in the pontine paramedian ventral region. On audiometric examination, there was bilateral sensorineural hearing loss. The patient was discharged with Valproic Acid 1000 mg/day, Quetiapine 200 mg/day. After discharge he underwent a neuropsychological evaluation that showed a cognitive decline.

Conclusion: There are various cases in the literature of pontine ischemias that have given simple and complex, terrifying and beautiful visual hallucinations. Patients generally had a normal state of consciousness, no delusions, and had sleep disturbances. Lesions of the pons involving the dorsal raphe nucleus result in the loss of ascending serotonin inhibition to the dorsal lateral geniculate nucleus. Consequently, an over-excited geniculate can generate visual hallucinations at the cortical level. These ischemias in the paramedian ventral pontine region may have damaged the nucleus of the acoustic nerve causing a bilateral sensorineural hearing loss and the nuclei of the lenticular formation which, through the serotinenrgic and dopaminergic dysregulation, gave rise to visual hallucinations. These visual hallucinations can be considered PH. Considering the cognitive impairment, assessed through neuropsychological assessment, and the cardiometabolic risk factors, we can also affirm that the previous psychiatric diagnosis of bipolar disorder could have delayed the neurological diagnostic investigations.