T2強調画像で等信号を呈した副鼻腔囊胞による両眼性鼻性視神経症の1例

A case of bilateral rhinogenic optic neuropathy due to paranasal sinus cyst manifesting isointensity mass in T2-weighted image

58歳女性の右眼に視力低下が突発し，その2日後に受診した。矯正視力は右眼0.02，左眼0.3であり，右眼に中心暗点，左眼に感度低下があった。中心限界フリッカー値（C-CFF）は右眼は測定不能，左眼は13Hzであり，右眼のRAPDが陽性であった。MRIで蝶形骨洞にT1強調画像で高信号，T2強調画像で等信号の病変が検出された。蝶形骨洞囊胞による両側鼻性視神経症と診断し，経鼻腔的に蝶形骨洞の手術を行った。洞内に褐色で粘稠な粘液があった。手術の6日後からステロイドパルス療法を3日間行い，矯正視力は左右眼とも1.0に回復した。副鼻腔囊胞はT2強調画像で高信号を呈するのが通例であるが，囊胞内の粘液が濃縮していたために等信号を呈したと解釈される。

A 58-year-old female presented with sudden blurring of vision in her right eye since 2 days before. Her corrected visual acuity was 0.02 right and 0.3 left. Central scotoma was present in the right visual field and sensitivity depression in the left. Central critical flicker frequency（C-CFF）was nonmeasurable in the right eye and 13Hz in the left. The right eye showed positive relative afferent pupillary defect（RAPD）. Magnetic resonance imaging（MRI）showed a lesion in the sphenoidal sinus. It showed high intensity in T1-weighted image and isointensity in T2-weighted image. She received intranasal sphnoidectomy under the tentative diagnosis of rhinogenic optic neuropathy. Brown sticky mucus was present in the sinus. After additional corticosteroid pulse therapy,her visual acuity recovered to 1.0 in either eye. Mucocele in the paranasal sinus usually shows high intensity in T2-weighted image by MRI. Isointensity in this patient appeared to be due to condensation of the mucus.