Posterior Fossa Arachnoid Cyst Presenting as Negative Symptoms of Psychosis.
Mr. X, a 28 year old male working as a farmer, presented to the psychiatry outpatient department with severe pain over the back and posterior part of the head for 5 months. Upon detailed history, a bystander noticed that he had reduced interaction with his family and friends for the last 1.5 years. He was not at all motivated to do any work for 6 months while often maintaining the same posture for hours for the last 2 months. The patient did not perceive it as a problem due to severe apathy during the examination of affect. He also complained of increased sound and pain sensitivity. He was found to be self-absorbed and smiling on very few occasions. Suspecting atypical symptoms, he was sent for neuroimaging (MRI brain). To our surprise, he was found to have a single extra-axial T1 hypo/T2 hyperintense lesion (2*4.5*2.5 cm) leaning on the left cerebellar hemisphere with a displacement of straight sinus right laterally. It was diagnosed as a posterior fossa arachnoid cyst causing a mild mass effect. The patient was referred to a neurosurgeon and surgical intervention was planned if he developed pressure symptoms in the future.
Mood symptoms, schizophrenia-like psychosis or amnestic symptoms are recorded as being associated with an arachnoid cyst.  Amidst controversy of a causative factor or an innocent bystander, it was noted that psychosis remitted soon after resection in many case reports[1,5]. It points towards the causative factor as per ICD-10 organic psychosis guidelines. There was no memory deficit, disinhibition, movement disorder or localizing sign to suspect organicity in the patient. Here the only atypical symptoms to suspect an organic cause were an occipital headache and it was highly possible that it would be missed. Negative symptoms as seen in this presentation are never mentioned in the literature. The negative symptoms were characteristic of psychosis as the patient did not express low mood but had restricted affect. In our case, negative symptoms could be due to cerebellar involvement which is found to cause cognitive deficit, disorganized speech, abnormal or catatonic behavior, and negative symptoms such as avolition, flat affect, and anhedonia in schizophrenia. 
Arachnoid cyst with psychosis can be left untouched or resected as per the pressure symptoms.  Often risperidone was used to treat psychotic symptoms but its efficacy for negative symptoms is questionable. So, an arachnoid cyst can show a varied presentation and should be strongly suspected in the case of atypical symptoms.
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Conflict of interest statement
The author declares no conflict of interest related to this manuscript.
[1.] Das S, Kartha A, Sumesh TP, Rajan V. Arachnoid cyst and psychosis: The troublemaker or innocent bystander. Indian J Psychol Med. 2017; 39(2): 194. doi: https://doi.org/10.4103/0253-7176.203107
[2.] da Silva JA, Alves A, Talina M, Carreiro S, Guimaraes J, Xavier M. Arachnoid cyst in a patient with psychosis: Case report. Ann Gen Psychiatry. 2007; 6: 16. doi: https://doi.org/10.1186/1744-859X-6-16
[3.] Mironov A, John S, Auerbach J, Jamaleddine G. Acute Onset of Psychosis in a Patient with a Left Temporal Lobe Arachnoid Cyst. Case Rep Med. 2014; 2014: 1-3. doi: https://doi.org/10.1155/2014/204025
[4.] Baquero GA, Molero P, Pla J, Ortuno F. A schizophrenia-like psychotic disorder secondary to an arachnoid cyst remitted with neurosurgical treatment of the cyst. Open Neuroimag J. 2014; 8: 1-4. doi: https://doi.org/10.2174/1874440001408010001
[5.] da Silva JA, Alves A, Talina M, Carreiro S, Guimaraes J, Xavier M. Arachnoid cyst and psychosis: a case report. Ann Gen Psychiatry. 2013; 28: 1. doi: https://doi.org/10.1186/1744-859X-6-16
[6.] Phillips JR, Hewedi DH, Eissa AM, Moustafa AA. The cerebellum and psychiatric disorders. Frontiers in public health. 2015; 3: 66. doi: https://doi.org /10.3389/fpubh.2015.00066
Soumitra Das obtained a bachelor's degree from the Agartala Govt. Medical College, Tripura, India in 2010, and a doctoral degree in psychiatry from the Govt. T D Medical College, Alappuzha, Kerala, India in 2015. Now he is working as a senior resident at the department of Psychiatry at the National Institute of Mental Health and Neuroscience, Bangalore, India. He is also a member of the Indian Psychiatric Society and IPS, Keraia. His research interests include ECT in clozapine resistant schizophrenia.
Department of Psychiatry, NIMHANS, Bengaluru, India.
correspondence: Soumitra Das. Mailing address: New Kabini Hostel, Room 119, NIMHANS, Bengaluru, India. Postcode: 560029. E-mail: firstname.lastname@example.org
[Shanghai Arch Psychiatry. 2018; 30(3): 202-203. doi: http://dx.doi.org/10.11919/j.issn.1002-0829.218005]
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|Publication:||Shanghai Archives of Psychiatry|
|Article Type:||Letter to the editor|
|Date:||Jun 1, 2018|
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