Arachnoid cysts (ACs) are intra-arachnoidal space occupying lesions, typically of a benign and congenital nature. They reportedly occur in more than 1% of the population, and are usually considered incidental when found in people with psychiatric symptoms. However, some authors argue for a putative causal relationship, based mainly on reports of improvement of a co-existing mental condition after surgical decompression of a cyst.

We describe a patient with schizophrenia-like psychosis and a temporal AC.

We will argue for the possibility of an association between the AC and psychotic symptoms.

We used a multidisciplinary approach to the patient, with emphasis given to diagnosis and treatment. We also reviewed the literature on the association between AC and psychosis.

We describe a 46-year-old woman with schizophrenia-like psychotic symptoms and visual hallucinations, refractory to antipsychotic treatment (including clozapine). Magnetic resonance imaging revealed a volumous AC with mass effect on temporal parenchyma. The patient was considered eligible for possible removal of the cyst, but refused to consult with a neurosurgeon.

The meaning of ACs found in patients with psychosis remains controversial. in our case, the lesion's volume and mass effect, the involvement of a region with a central role in the pathophysiology of psychosis, and the refractoriness to clozapine treatment, all argue for a causal role in the patient's psychosis. Surgical decompression might have improved the patient's outcome. Yet, the lack of a solid evidence-base made it ethically unacceptable to advocate for this option in a reluctant patient.