Arachnoid cysts are rare, benign space-occupying lesions formed by an arachnoid membrane containing cerebrospinal fluid (CSF). They are often discovered as incidental findings found on imaging. Occasionally they may produce symptoms because of expansion or bleeding.

The coexistence of arachnoid cysts with psychiatric disturbances in adolescents had not been closely covered in the literature. Recent descriptions of aphasia and attention-deficit disorders associated with these cysts indicate that we do not fully understand this entity. There is also no acceptable explanation for the male preponderance and increased incidence on the left side.

The appearance of some references that focus on a possible link between arachnoid cysts and psychotic symptoms in adolescents has increased the interest in this subject.

This case report describes the treatment of a 17-year old male adolescent, characterized by “negative” psychotic symptoms, reduced affect, unfunctioning behavior, headaches and vision problems. An arachnoid cyst was found on the temporobasilaris left brain side on magnetic resonance image. His psychotic symptoms were suspected to be induced by the arachnoid cyst. The patient was treated with an outpatient antipsychotic therapy (olanzapin) during one year and shown improvement, but without a complete remission of the psychotic symptoms.

It is difficult to discus whether the lesion had influence on the patient’s psychiatric symptoms or not, but clinical features and treatment modalities points this possibility. However, the co morbidity of neurological and psychiatric symptoms in adolescence raises problems when it comes to choosing the therapeutic guidelines.