右後頭葉髄膜腫摘出後に一過性に出現したCharles Bonnet syndromeの1例

Transient Charles Bonnet Syndrome after Excision of a Right Occipital Meningioma: A Case Report

Ⅰ．はじめに

　幻視症の1つにCharles Bonnet syndrome（CBS）がある．末梢性の視機能障害をもつ高齢者に好発する要素性あるいは有形性幻視であり，患者は意識清明で知的障害がないと定義されている．今回われわれは，糖尿病性網膜症による視覚障害のある患者において，右後頭葉髄膜腫摘出術後に一過性に出現したCBSを経験したので，文献的考察とともにその発生機序を検討する．

　Charles Bonnet syndrome is a condition characterized by visual hallucinations. These simple or complex visual hallucinations are more common in elderly individuals with impaired peripheral vision. The current report describes a case of transient Charles Bonnet syndrome appearing after the removal of a meningioma. The patient was a 61-year-old man who already had impaired visual acuity due to diabetic retinopathy. Brain MRI revealed a cystic tumor severely compressing the right occipital lobe. Starting on day 2 postoperatively, the patient was troubled by recurring visual hallucinations involving people, flowers, pictures, and familiar settings（the train and a coffee shop). These continued for 3.5 months. This period roughly coincided with the time for the occipital lobe to recover from the compression caused by the tumor, a fact that was confirmed by several MRI scans. ¹²³I-IMP SPECT performed 1 month after the surgical operation showed an area of hypoperfusion in the right parieto-occipital lobe. Based on the patient's clinical course and MRI findings, the mechanism of onset of visual hallucinations in this patient was put forward. The release of pressure in the brain by tumor removal and subsequent recovery changed the blood flow to the brain. This triggered visual hallucinations in the patient, who was already predisposed to developing Charles Bonnet syndrome because of diabetic retinopathy. This case is interesting since it indicates that central neurological factors, as well as visual deficits, may induce the appearance of visual hallucinations in Charles Bonnet syndrome.