実験的脳梗塞のCT像と組織像—血液脳関門，脳微小循環およびcontrast enhancement陽性出現機序について

CT SCAN AND HISTOLOGY OF EXPERIMENTAL CEREBRAL INFARCTION:BLOOD-BRAIN BARRIER, MICROCIRCULATION AND MECHANISM OF CONTRAST ENHANCEMENT

　抄録　85匹の猫を用い，中大脳動脈閉塞モデルを作成し，最短6時間目，最長35日目にplainおよびenhanced CTを施行，組織像と対比した。脳梗塞の各時期，とくにcontrast enhancement陽性期における血液脳関門および微小循環を調べるため，fluorescein静注およびcarbon perfusionを行った。CT像の推移から脳梗塞は，浮腫前期，浮腫期，浮腫消退期および空洞期の4期に区分しえた。浮腫消退期では，CE陽性率が高く，CE陽性領域の組織像の特徴は，毛細血管と貪食細胞の出現である。この領域ではfluorescein stainの輝きが非常に強く，BBB機能障害が高度であることが示された。CE陽性領域でのcarbon fillingは全般的に不良であるが，一部でcarbon depositが認められ，局所的には微小循環の良好な部位が存在する。carbon depositの部位では，血管内ヨードのみでCE陽性となりうるが，他の多くの領域では微小循環が不良であるため，CE陽性となるためには血管外へ漏出したヨードが存在するはずである。CE陽性例で組織内ヨード含有量を測定したところ，CE陽性領域全般に極めて高値を呈した。したがって，CE陽性出現のためには，血管内のみでなく血管外漏出ヨードも関与する。

Cerebral infarction models were made by occlud-ing the right middle cerebral artery (MCA) in 85 cats. Plain and enhanced CT scan were done at various interval after MCA occlusion. Follow-up period after MCA occlusion ranges from 6 hours to 35 days. Every model was studied histo-logically following CT scan. Blood-brain barrier (BBB) function and microcirculation in the region of cerebral infarction were studied simultaneously by using the technique of intravenous fluorescein injection and carbon perfusion in 28 cats. To reveal the mechanism of positive contrast enhan-cement (CE) in cerebral infarction, quantitative study of iodine in the brain tissue was done in 6 cats.

Cerebral infarction was divided into 4 different stages by characteristics on CT scan. First stage, named pre-edema stage, ranges from 6 hours to 24 hours after occlusion. Second stage, namededema stage, ranges from 12 hours to 5 days. Third stage, named edema-diminishing stage, ranges from 4 days to 24 days. Forth stage, named cavity stage, ranges from 20 days to 35 days.

CT scan of pre-edema stage shows no abnormal findings. Edema stage shows diffuse low density area (LDA) in the right cerebral hemisphere with mass effect. Edema-diminishing stage shows loca-lized LDA without mass effect. Cavity stage shows shrunk LDA with ipsilateral ventricular dilatation.

In edema-diminishing stage, positive CE was identified in high percentage (81%). In these positive CE cats, infarcted region is identified as impaired carbon filling from the study of carbon perfusion. But in some cats, there is carbon de-posit which indicates good microcirculation in the infarcted region. Fluorescein stain which indicates the region with BBB dysfunction extends not only in the positive CE region but also the surroun-dings of the positive CE region.

Histological characteristics of positive CE re-gion is the appearance of dilatated capillaries and phagocytes named "gitter cell". By detail study of histological appearance, positive CE region was divided into 3 territories. One is the territory with a large number of dilatated capillaried sur-rounded by gitter cells (A), another is the ter-ritory with a large number of gitter cells with a few capillaries ( B) and the last is the territory with brain parenchym suffering from ischemic insult associated with a small number of capil-laries and/or gitter cells (C).

From a point of tissue reversibility, territory (A) and ( B) are thought to be irreversible while territory (C) can be reversible. If reconstructive surgery such as STA-MCA anastomosis should be performed in the stage of positive CE, territory ( C) can survive. On the other hand, the risk for provocation of hemorrhagic infarction or aggrava-tion of luxuary perfusion may occur because that the fluorescein study showed the capillaries in the infarcted region to have been destructed of its BBB function.

Positive CE region generally shows impaired carbon filling which indicates poor microcircula-tion. As so, intravascular component of iodine can not fully explain the positive CE. From the quantita-tive study of iodine, positive CE region contains very high level of iodine with comparison to the same region of the opposite hemisphere. The mecha-nism of positive CE depends not only on the intravascular component but also on the extravas-cular component of iodine.