This patient's clinical picture is characterised by the insidious development of psychotic symptoms: delusional ideas with a hypochondriac content; complex auditory/verbal hallucinations in the second and third persons; and behavioural changes with aggressive behaviour.
The patient did not display the typical characteristics which make it easier to distinguish between non-organic psychosis and organic psychosis such as abnormal vital signs, recent memory changes, age above 40, disorientation and an altered state of consciousness [1
Given the existence of toxic levels of cannabinoids in the patient's urine it is not possible to exclude the hypothesis of a psychosis with a toxic aetiology. However, there was no substantial improvement once the cannabinoids values fell to normal levels.
The anomalous pneumatisation of the frontal sinus found next to the cyst sheds some light into its origin by suggesting a probable congenital malformation instead of a secondary aetiology related to the traumatism which the patient suffered at the age of 16.
In fact, it is difficult to be sure whether we are in the presence of an organic psychotic disorder or of a simple coincidence in which the arachnoid cyst is just an 'innocent bystander' to the development of a functional psychosis.
Although the cyst seems to be congenital, it did not cause any symptoms earlier in life. Nevertheless arachnoid cysts may enlarge and interfere with adjacent neural structures or CSF circulation [7
]. The mass effect shown on the neuroimaging studies suggests that this might be the case, and what started as an 'innocent bystander' may not be so innocent after all.
Remission of symptoms following surgical treatment [21
], association of psychiatric symptoms with neurological changes [11
], advanced age, absence of family history, evidence of compression of the temporal lobe and neighbouring structures [12
]., and changes in the neuropsychological and neurophysiological tests [11
] are all mentioned as factors that suggest an etiologic relationship of arachnoid cysts to the psychiatric disorders. The presence of some of these factors – particularly the evidence of hypoplasia of the left temporal lobe (figure ), and the neuropsychological changes compatible with those described for orbitofrontal lesions (figure ) [24
] – strengthens the possibility that this lesion played a part in the etiopathogeny of the psychotic symptoms.
Other cases of psychoses that are associated with arachnoid cysts have been described in patients with an injured left temporal lobe [11
]. Structural changes of the temporal lobe, both at the level of the median structures and of the temporal circumvolution, have been associated with schizophrenia [25
The patient said there were periods in which the words people said appeared to make no sense. This description is compatible with a dysphasia, which in structural terms could mean that Wernicke's region was compromised by the direct mass effect of the cyst. However, during the inpatient stay the patient did not report any such episodes.
According to current clinical practice, there are two aspects to the therapeutic approach of organic psychotic disorders: i. controlling the symptoms and ii. correcting the etiological situation. In the specific case of arachnoid cysts the need for a surgical approach is neither clear nor uniform: intracranial hypertension or progressive hydrocephaly are usually the only situations where surgery is mandatory [7
]. If neither of these indications is present and there are no focal neurological signs, given both the morbidity associated with surgery and the fact that this type of lesion can disappear spontaneously, the attitude is generally conservative [7
]. However, an analysis of the literature shows that although this is the most common choice, there have been cases in which surgical intervention was specifically adopted as a therapeutic approach to the psychotic symptoms.
The first patient described in the literature with an acute psychotic disturbance and an arachnoid cyst in the left temporal region, showed a total remission of symptoms after the cyst had been surgically removed [18
]. Colameco et al
] describe the case of a patient with episodes of derealization and emotional lability associated with the presence of an arachnoid cyst, in which the symptoms also displayed total remission following the cyst's removal. In a case series by Kohn et al
] that describes eight patients with arachnoid cysts associated with psychiatric disturbances, only one of the cases with psychotic symptoms underwent surgery to remove the cyst. Curiously enough, this patient was the only to experience complete remission of his symptoms. In a recently described case of atypical psychosis associated with an arachnoid cyst, Vakis et al
] found intermittent rises in the intracranial pressure. Although these rises did not result in any neuroimaging changes, the authors considered them to be a plausible etiopathogenic factor in the appearance of the psychotic symptoms in that particular female patient. The surgical removal of the lesion was followed by a clear improvement. Wong et al
] describe the interesting case of a female patient with an arachnoid cyst in the trigone of the right lateral ventricle, which was associated with very short psychotic episodes that arose after the patient had been lying down in bed for 1–2 hours. They called these episodes 'positional psychosis', and suggested that the decubitus position led the cyst to cause a local ischemia in the temporal horn, with the consequent appearance of psychotic symptoms. In this case, it was also decided to operate the lesion, and this led to the total disappearance of the psychotic symptoms in just four days.
In other cases [12
] a conservative choice was made and the only treatment was pharmacotherapy with antipsychotics, leading to relative improvements in the psychotic symptoms. However, patients in whom neuropsychological alterations were initially described did not improve much during the follow-up period [13
In the case we present, risperidone was selected due to the good results it has shown in psychosis associated with a general medical condition, including a case of psychosis associated with an arachnoid cyst [13