Diagnosis of an Arachnoid Cyst in a Patient Presenting With Uncommon Depressive Symptoms: Case Report.

Arachnoid cysts are most commonly asymptomatic and usually do not need any active treatment. Currently, psychiatric symptoms are seldom taken into consideration during treatment evaluations in this patient population. We present this case of a young man who was treated in our hospital for signs of depression. Due to his atypical presentation, we decided to perform a brain MRI, which detected the presence of an arachnoid cyst located in the right insular region. A further diffusion tensor imaging tractography study was performed, which showed variations in the fractional anisotropy asymmetry indexes. Our case supports the notion that arachnoid cysts can induce different psychiatric conditions, even in the absence of alterations in the neurological examination. Furthermore, it supports the importance of ordering brain imaging studies to rule out the presence of arachnoid cysts, especially if the clinical manifestations and/or age of presentation are unusual. In light of the knowledge of functional neuroanatomy, there is a need for more neuroimaging studies in order to clarify the mechanisms by which certain brain-occupying lesions can induce structural and functional changes.