画像上視索に浮腫を認めたラトケ囊胞の1例

MR Imaging Study of Edema along the Optic Tract in Patient with Rathke's Cleft Cyst

　要旨　患者は80歳女性。口渇，多飲，多尿を主訴に当科紹介入院となった。MRI検査にてトルコ鞍から鞍上部にかけてガドリニウムによる増強効果を示す囊胞性腫瘤を認め，下垂体柄の腫大も認めた。また，FLAIR画像で両側の視索が高信号を呈したため，術前診断として頭蓋咽頭腫を考えた。入院時の視力は右（0.5），左（0.3），視野検査では異常を認めず，内分泌学的検査は基礎値では，プロラクチン47.9ng/mlの上昇を認めた。トルコ鞍内の病変に対し内視鏡下経鼻的経蝶形骨洞手術を施行した。病理所見にて下垂体前葉・後葉に多数のリンパ球浸潤を認め，また一部に平上皮化生を認めた。FLAIR画像において視索が高信号を呈する疾患としては，頭蓋咽頭腫や視神経膠腫などが報告されている。しかしながら，本例のように，リンパ球性下垂体炎を伴ったラトケ囊胞でも同様の所見を呈する可能性が示唆され，診断の一助となると考えられた。

　We report an 80-year-old woman who was admitted to our hospital with symptoms due to diabetes insipidus. Magnetic resonance （MR） imaging demonstrated a sellar/suprasellar cystic lesion with marginal enhancement and the thick pituitary stalk. The MR imaging depicted edema spreading along the optic tract on fluid-attenuated inversion recovery （FLAIR） images. Upon neurological examination at the time of admission, there were no abnormal findinds affecting the field of vision or visual acuity. In endocrinological examination, the basal plasma values of pituitary hormones were within normal range except for that of prolactin, which was 47.9 ng/ml. The preoperative diagnosis was craniopharyngioma, and the intrasellar mass was partially removed by the endoscopic transnasal transsphenoidal approach. Postoperative histopathological examination revealed Rathke's cleft cyst associated with squamous metaplasia. Lymphocytic infiltration was also confirmed in both the anterior and posterior pituitary lobe. The postoperative course was satisfactory. Edema spreading along the optic tract was reported as a characteristic MR imaging finding for diagnosis of craniopharyngiomas or optic nerve glioma. However, it is suggested that edema of the optic pathway seems to be caused not only by craniopharyngioma but also other suprasellar lesions. It was a rare case of secondary lymphocytic hypophysitis caused by Rathke's cleft with edema along the optic tract.

（Received : January 9, 2004）