脳原発リンパ腫様肉芽腫症の1例

Primary Central Nervous System Lymphomatoid Granulomatosis: A Case Report

Ⅰ．はじめに

　リンパ腫様肉芽腫症（lymphomatoid granulomatosis：LYG）は稀なリンパ球増殖性肉芽腫性の全身性疾患で，多くは肺に単発あるいは多発性の腫瘤性病変が認められる．病変が皮膚，腎臓，中枢神経系など多臓器に及ぶ場合もあるが，他臓器に病変を伴わない脳原発のLYGは極めて稀である．今回，われわれは視野障害にて発症した脳原発LYGの切除例を経験したので，文献的考察を加えて報告する．

　Lymphomatoid granulomatosis (LYG) is a rare Epstein-Barr virus-associated multisystem lymphoproliferative and granulomatous disease histologically characterized by angiocentric and angiodestructive cellular infiltrate. LYG usually involves the lungs,skin,kidneys and brain,but isolated central nervous system LYG has been reported rarely. We describe a 57-year-old man with histologically proved LYG confined to the brain. The patient complained of visual disturbance,and was admitted to our hospital. Gadolinium-enhanced T1-weighted MRI showed irregular,partly cystic and lobulated enhancement in the left occipital lobe,suggesting the presence of possible neoplastic lesions such as glioma,malignant lymphoma or metastatic brain tumor. We performed surgical resection of the lesion. Histological and immunohistochemical examinations of the tumor showed angiocentric polymorphic infiltration and granulomatous reaction,consisting of CD3-positive small lymphocytes and CD20-positive large atypical cells. Subsequently,in situ hybridization study for EBER (Epstein-Barr virus encoded small RNA) was performed and proved that the large atypical cells were positive for EBER. These findings were compatible with LYG. We emphasize that the possibility of LYG should be considered in the differential diagnosis of any ring-like enhancing mass lesions on MR images,though less specific for LYG. Histopathological examination is indispensable for the final diagnosis and the choice of an optimal treatment strategy.