Arachnoid cyst in a patient with psychosis: Case report



The aetiology of a psychotic disturbance can be due to a functional or organic condition. Organic aetiologies are diverse and encompass organ failures, infections, nutritional deficiencies and space-occupying lesions. Arachnoid cysts are rare, benign space-occupying lesions formed by an arachnoid membrane containing cerebrospinal fluid (CSF). In most cases they are diagnosed by accident. Until recently, the coexistence of arachnoid cysts with psychiatric disturbances had not been closely covered in the literature. However, the appearance of some references that focus on a possible link between arachnoid cysts and psychotic symptoms has increased the interest in this subject and raised questions about the etiopathogeny and the therapeutic approach involved.

Clinical presentation

We present the clinical report of a 21-year-old man, characterised by the insidious development of psychotic symptoms of varying intensity, delusional ideas with hypochondriac content, complex auditory/verbal hallucinations in the second and third persons, and aggressive behaviour. The neuroimaging studies revealed a voluminous arachnoid cyst at the level of the left sylvian fissure, with a marked mass effect on the left temporal and frontal lobes and the left lateral ventricle, as well as evidence of hypoplasia of the left temporal lobe. Despite the symptoms and the size of the cyst, the neurosurgical department opted against surgical intervention. The patient began antipsychotic therapy and was discharged having shown improvement (behavioural component), but without a complete remission of the psychotic symptoms.


It is difficult to be absolutely certain whether the lesion had influence on the patient’s psychiatric symptoms or not.

However, given the anatomical and neuropsychological changes, one cannot exclude the possibility that the lesion played a significant role in this psychiatric presentation. This raises substantial problems when it comes to choosing a therapeutic strategy.


Psychotic disorders which may be caused by either functional or organic conditions, are clinical entities characterised by changes in perception and thinking, thus interfering with the patient’s social performance [1].

In DSM-IV, psychosis with an organic aetiology is named “Psychotic Disorder due to a General Medical Condition” and has two subgroups: i) with hallucinations, and ii) with delusions [2]. Traumatisms or structural changes of the brain such as space-occupying lesions; biochemical changes (including intoxication with drugs); organ failure; infections; and nutritional deficiencies are all examples of causes of psychoses that are secondary to a general medical condition [1,36].

Arachnoid cysts are benign space-occupying lesions containing CSF. They are rare lesions and account for only 1% of all intracranial space-occupying lesions [7]. From an etiological point of view we should distinguish between true cysts (of a congenital nature) and false ones, which are secondary to the post-inflammatory accumulation of CSF during cranial traumatisms, infections or intracranial haemorrhages [7,8]. Arachnoid cysts can appear in any area of the central nervous system, though they are more frequent in the Sylvian fissure, where they are found in about 50% of cases [8]. They occur roughly twice as often on the left side as they do on the right, although the reason for this is unknown [79] and there is a preponderant ratio of 3:1 in male as opposed to female patients [9].

Arachnoid cysts are often diagnosed before adulthood (60–90% prior to the age of 16) [8]. In most cases diagnosis is accidental, and it may even result from a fortuitous discovery during a post-mortem examination [7,8,10].

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