眼窩内壁骨折整復術直後に視力障害をきたした1例

Visual impairment after medial orbital fracture repair

要約　目的：眼窩内壁骨折整復術中に外傷性視神経症をきたしたと考えられる症例を経験したため報告する。

症例：79歳，男性。転倒外傷による左眼窩内側壁骨折治療のため形成外科を受診。CT上，外眼筋や軟部組織の嵌頓は認めないが，外転制限および複視を認め，1週間以上改善がみられず，手術適応となった。術前の矯正視力（小数視力）は1.0であった。術直後より視力障害を訴え，精査のためCTが施行されたが血腫などは認めなかった。プレートによる視神経の圧迫が原因と疑われ，プレート抜去が施行された。その後も視力が改善しなかったため，当科紹介となった。診察時の所見は左眼光覚−，直接対光反射−，間接対光反射＋，相対的瞳孔求心路障害陽性，前眼部や眼底に特記すべき所見はなかった。造影MRI上明らかな視神経の断裂は認めなかったが，辺縁が不整な部位があり，医原性の外傷性視神経症を疑いステロイドパルスを1クール施行した。その後は保存的加療の方針となり，術後6か月時点で矯正視力は0.2まで改善している。

結論：眼窩骨折術後に眼窩コンパートメント症候群のため視力障害をきたした症例報告はあるが，それ以外の原因で術直後に視力障害をきたす症例は非常に稀である。術直後に視力障害をきたしたとする症例報告2例ではプレート抜去などの眼窩内減圧により視力は改善したとされている。本報告では視力障害の発覚後早期にプレートの抜去が施行されたが，視力改善が乏しく，術中に視神経が直接損傷されていたと考えられた。

Abstract　Purpose：We report a case of suspected traumatic optic neuropathy during orbital medial wall fracture surgery.

Case：A 79-year-old man presented to the Department of Plastic and Reconstructive Surgery for treatment of a left medial orbital wall fracture due to a fall injury. CT showed no external ocular muscles or soft tissue fits, but there was limited abduction and diplopia, which did not improve over 1 week, and the patient was indicated for surgery. His preoperative best corrected visual acuity（decimal acuity）was 1.0. Immediately after surgery, the patient complained of visual disturbance and underwent CT examination. No hematoma or plate dislocation was found；however, the optic nerve was believed to be compressed by the plate, thus the plate was removed. As there was still no improvement in his visual acuity, he was referred to our department. On examination, the patient had no light perception, negative direct light reflex, positive indirect light reflex, and positive relative afferent pupillary response defect in the left eye. There were no specific findings in the anterior or fundus of the left eye. Contrast-enhanced MRI showed no obvious optic nerve tear, but there was an area with irregular limbus, and a course of steroid pulses was administered on suspicion of iatrogenic traumatic optic neuropathy. Following this, the patient was treated conservatively, and his best corrected visual acuity improved to 0.2 at 6 months after surgery.

Conclusion：Although there are some case reports of visual impairment due to orbital compartment syndrome after orbital fracture surgery, cases of visual impairment immediately after surgery due to other causes are extremely rare. In the two case reports of postoperative visual impairment, visual acuity was improved by intraorbital decompression, such as plate removal. In the current case, the plate was removed immediately after the visual impairment was discovered, but there was little improvement in visual acuity, suggesting that the optic nerve was directly damaged during the surgery.