Impulsive Homicide Associated With an Arachnoid Cyst and Unilateral Frontotemporal Cerebral Dysfunction

Area of Science:

• Neuroscience
• Neurology
• Forensic Psychiatry

Background:

• Acquired disturbances in social conduct are often linked to ventromedial frontal lobe injury.
• Understanding the neurobiological underpinnings of sudden-onset violence is crucial for clinical and forensic applications.

Purpose of the Study:

• To investigate the neuroanatomical and functional correlates of an abrupt, uncharacteristic violent act in a 65-year-old man.
• To explore the role of ventral prefrontal dysfunction in stimulus-bound aggression.

Main Methods:

• Magnetic resonance imaging (MRI) to identify structural brain abnormalities.
• Neuropsychological testing to assess cognitive functions, including prospective memory and executive functions.
• Electroencephalography (EEG) and positron emission tomography (PET) to evaluate brain activity and metabolism.
• Assessment of autonomic responses to affective stimuli.

Main Results:

• A large arachnoid cyst in the left Sylvian fissure was identified, causing effacement of ventral frontal, anterior temporal, and insular cortical gyri.
• Mild impairments in prospective memory and executive functions were noted, alongside decreased EEG amplitude in the left fronto-temporal region.
• PET revealed reduced glucose metabolism in the left frontal and temporal lobes, and diminished autonomic responses to affective stimuli.

Conclusions:

• The patient's violent behavior is suggested to be stimulus-bound aggression, triggered by a physical threat.
• Ventral prefrontal dysfunction, evidenced by structural and functional brain abnormalities, likely impaired learned social restraints, leading to the aggressive act.
• This case highlights the potential for focal brain lesions to precipitate significant changes in social conduct and aggression.