CTスキャンとMRIで画像診断が異なった眼窩腫瘍の2例

Computed tomography and magnetic resonance imaging gave conflicting results in two cases of orbital tumor

　X線CTとMRIで画像診断所見が異なった眼窩先端部に限局した2症例を経験したので報告する。両症例ともマーカス・ガン瞳孔，中心暗点を認め，視神経障害を早期から伴っていた。X線CTでは境界の不鮮明な腫瘍陰影が認められ眼窩炎性偽腫瘍が疑われたが，MRIでは境界が鮮明であり，視神経鞘髄膜腫と診断した。X線CTで腫瘍の辺縁が不明瞭であったのはbeam hard-ening artifactのためであったと思われた。これらの症例のように眼窩先端部に限局した小病変ではMRIがX線CTより有用である。

We examined two cases of small orbital tumor located in the apex. Optic nerve disturbances in-cluding Marcus Gunn pupil and central scotoma were present in both cases. Computed tomography, CT, failed to delineate well-defined tumor mass,leading us to the diagnosis of orbital pseudotumor. Well-delineated tumor was shown later by mag-netic resonance imaging, MRI, leading to the final diagnosis of optic nerve sheath meningioma. CT failed to clearly outline the tumor because of beam hardening artifact. MRI seemed to give more reli-able data than CT in cases of small tumors located in the orbital apex.