単純MRIでは診断困難であった鼻性視神経症の1例

A case of rhinogenous optic neuropathy: diagnostic challenges with non-contrast MRI

要約　目的：鼻性視神経症は，眼窩に隣接する副鼻腔病変によって視神経に障害が及び，急性に視力低下や視野障害を引き起こす疾患で，早期診断と治療が視力回復のために重要である。単純MRIでは視神経への炎症が確認できず，造影MRIで初めて視神経への波及が判明し，手術により視力が回復した症例を報告する。

症例：35歳，女性。右視力低下と視野欠損を訴え眼科受診となった。既往歴は特になく，耳鼻咽喉科で副鼻腔炎と診断されたが，眼症状が続いたため当科で精査を実施した。単純MRIでは視神経の異常は確認されなかったが，造影MRIで右上顎洞から視神経周囲へ炎症が波及している所見が認められたため，鼻性視神経症の診断となった。内視鏡下副鼻腔手術を施行し，術後1週間で矯正視力0.06から1.0まで回復し，1か月後には視野障害も改善して良好な経過をたどった。

結論：単純MRIでは診断困難な鼻性視神経症でも，造影MRIにより視神経周囲への炎症波及を明確に評価できる可能性がある。CTや単純MRIで異常が確認できない場合，造影MRIを早期に導入することで診断精度が向上し，適切な治療を通じて視力予後を改善できることが示唆された。

Abstract　Purpose：Rhinogenous optic neuropathy is a condition in which lesions in the paranasal sinuses adjacent to the orbit extend to the optic nerve, leading to acute visual impairment and visual field defects. Early diagnosis and treatment are crucial for vision recovery. We report a case of optic nerve inflammation, undetected on non-contrast magnetic resonance imaging（MRI）, which was successfully identified using contrast-enhanced MRI, enabling prompt surgical intervention and subsequent visual recovery.

Case：A 35-year-old woman presented with visual impairment and loss of visual field in her right eye. She had no relevant medical history and was initially diagnosed with sinusitis at an otolaryngology clinic. However, due to persistent ocular symptoms, a detailed examination was conducted at our department. While non-contrast MRI revealed no optic nerve abnormalities, contrast-enhanced MRI identified inflammation spreading from the right maxillary sinus to the optic nerve, leading to a diagnosis of rhinogenous optic neuropathy. Endoscopic sinus surgery was performed；her best-corrected visual acuity improved from 0.06 to 1.0 within one week postoperatively. Further improvement in visual field defects were observed one month later.

Conclusion：Contrast-enhanced MRI can be valuable in assessing optic nerve inflammation in cases where non-contrast MRI is inconclusive for diagnosing rhinogenous optic neuropathy. Early utilization of contrast-enhanced MRI can improve the diagnostic accuracy of optic neuropathy and facilitate timely treatment for better visual outcomes, especially when computed tomography（CT）or non-contrast MRI shows no abnormalities.