PM473. A case of schizophrenia coexistence with a large cerebellar arachnoid cyst

Background: Many intracranial lesions can induce psychotic symptoms. Arachonoid cyst is one of the suspicious etiologies. A possible link between arachnoid cyst and psychosis gives an interest to the pathogenesis of psychotic symptoms. Here, we present a case of schizophrenia with a large cerebellar arachnoid cyst. Case Presentation: Ms. Lu is a 31-year-old woman with schizophrenia for 7 years without regular treatment. She was admitted because of auditory hallucinations, referential and persecutory delusions accompanying irritable mood and aggressive behaviors. She described that her parents were evil and wanted her to die. Series of examinations were arranged. Neurological examination revealed some stereotype behaviors and easily falling down. The blood counts, serum chemistry and EEG were normal. Brain MRI revealed an arachnoid cyst about 6.9 x 4.1 x 3.1 cm over right posterior fossa with cerebellar compression. Neurosurgery was consulted and no emergent pathologic change was detected, then routine follow-up was recommended. Her psychotic and aggressive symptoms gradually improved under Olanzapine 30mg/day and Depakine 1200mg/day. Brain Imaging: Discussion: It is difficult to ascertain whether cerebellar arachnoid cyst influences psychotic symptoms. I speculate that cerebellar arachnoid cyst is associated with schizophrenia in this case for following reasons: (1) Cerebellum is crucial in cognition and several psychiatric disorders including schizophrenia. (2) Ms. Lu has soft stereotype behaviors and easily falling down with psychotic symptoms. (3) The cyst was large enough to compress right lobe and adjacent structures. (4) Ms. Lu was unresponsive to regular-dose Olanzapine (20mg/day) monotherapy and required Olanzapine 30mg/day and additional Depakine 1200mg/day. In the literature review, misconnections between cortex and cerebellum through thalamus (Cortico-cerebellar-thalamic-cortical circuit) may explain part of schizophrenic symptoms. I propose that Ms. Lu’s arachnoid cyst at right posterior fossa with cerebellar compression may cause abnormality in above circuit and result in psychotic symptoms. Further research is warranted to elucidate underlying mechanisms.