黄斑分割する同名半盲をきたした半側空間無視の2例

Two cases of unilateral spatial neglect accompanying macular splitting

要約　目的：筆者らが以前に報告した右皮殻出血後の半側空間無視に伴う左同名半盲の2例では，正中より左側にも不安定な反応があった。このたび，前回の症例とは異なり，黄斑分割する同名半盲をきたした半側空間無視の2例を経験した。

症例：症例1は37歳，男性（右頭頂葉皮質下出血）。症例2は65歳，女性（右頭頂葉皮質下出血）。線分二等分試験，時計描写試験において半側空間無視のパターンを呈し，黄斑分割する左同名半盲を認めた。発症2か月後には半側空間無視は回復し，同名半盲も改善した。

考察：半側空間無視は右脳病変により左に発症する。右視野と左視野の相応する部位に同時に視覚刺激を与えた際に，一側を検出できない“視覚消去現象”がみられるが，正中をはさまない2つの指標に対しても，相対的に左側の指標が意識されにくい。左側の視野検査のときは中心を固視しつつ，より左方の指標を検索するが，相対的に左方の指標は感知されにくいため，左同名半盲様となる。半側空間無視には，正中に関係なく左側を無視する対象依存性と，正中より左側のみを無視する主体性の2パターンがある。以前の症例は，正中より左方の指標にも不安定な反応があり，対象依存性である。今回の症例は，正中より左方では全く反応がなく，主体性と思われる。

結論：半側空間無視に伴う，異なる2つのパターンの同名半盲を経験した。右脳病変後に，黄斑分割する左同名半盲，または左右の同一性が低い左同名半盲を認めたときは，半側空間無視の関与が疑われる。

Abstract　Purpose：We previously reported two cases of left homonymous hemianopia with unilateral neglect after right cutaneous hemorrhage. In these two cases, an unstable reaction remained to the left of the midline. Subsequently, we experienced two cases of unilateral neglect that caused homonymous hemianopia with macular division that was different from the previous cases.

Cases：Case 1：37-years-old male. Case 2：65-years-old female. A right subcortical hemorrhage was confirmed in both patients. A typical pattern of unilateral neglect was confirmed in the line-bisection-test and the clock-drawing-test, which was accompanied with a left homonymous hemianopia with macular splitting. Two months after the onset, the unilateral neglect recovered, and homonymous hemianopsia improved.

Findings：Unilateral neglect develops on the left side with right-sided brain lesions. A “visual extinction phenomenon” is observed, in which one side of the signal of the corresponding region in the right and left visual fields is not detected. It is difficult to search to the left side even when the visual signals are present only on either side of the midline. When the visual field is examined, the patients search for markers to the left of the center while fixating on the center. Left homonymous hemianopia occurs because the left marker is difficult to perceive.

There are two types of neglect；stimulus-centered neglect in which signals further to the left are not able to be searched, and body-centered neglect in which the signals to the left of the midline are not able to be searched. Our previous cases were stimulus-centered neglect with erratic responses to the left of the midline. In the present cases, there was no reaction on the left side of the midline, and it appears to be body-centered neglect.

Conclusions：We experienced two different patterns of homonymous hemianopia associated with unilateral neglect. In cases of left homonymous hemianopia with macular division or left homonymous hemianopia with low bilateral identity, the involvement of unilateral neglect should be considered.