経リンパ脳脊髄液吸収経路に関する検討（第2報）—頭蓋内圧亢進時の経リンパ脳脊髄液吸収について

CEREBROSPINAL FLUID ABSORPTION INTO LYMPHATIC SYSTEM IN CONDITION OF INCREASED INTRACRANIAL PRESSURE

I．はじめに

　脳脊髄液（以下髄液）がリンパ系に吸収されるといういわゆる"経リンパ髄液吸収路"に関しては，1869年にSchwalbe^17）が動物実験で初めて確認して以来，各種の物質をくも膜下腔に注人して同様な事実を認めた報告がすでに多くなされている^14,15,19）。しかし，この吸収路が種々の病態においていかなる機能を果すかについては報告も少なく，頭蓋内圧亢進時のこの吸収路の機能について論じたものは認められない。

　最近われわれはくも膜下腔に色素を注入してこの吸収路の病理組織学的検索を行い，その色素吸収経路について報告した^2）。今回われわれはその吸収路の主なdrainerである頸部リンパ管よりリンパ排液量を測定し，さらに^99mTc-DTPAを髄腔内投与してそのリンパ管よりリンパ液を採取してそのRI countingを行つた。この際，頭蓋内圧各段階におけるそれらの経時的推移について観察し，頭蓋内圧亢進時のこの吸収路の機能について考察を加えた。

Dynamics of cerebrospinal fluid (CSF) absorption into cervical lymphatic flow was studied in 31 mongrel adult dogs in condition of normal and increased intracranial pressure (ICP). The experi-ment was composed of two different investigations ; observation on volume changes in cervical lymph outflow (Experiment I) and simultaneous radio-isotope counting in systematic blood, CSF and lymphatic fluid (Experiment II).

Both cervical lymph ducts were cannulated under intravenous pentobarbital anesthesia and the out-flow volume of lymphatic fluid was measured every 30 minutes. In Experiment I, levels of ICP were controlled by continuous infusion of artificial CSF through the lumbar subarachnoid space at the pressure ranges of 300 and 700mmH₂O. Compared to the control volume of 18.1+2.0μl/min, cervicallymphatic fluid increased as the response to loaded ICP levels, being approximately 2.3 and 5 folds at the respective pressure ranges of 300 and 700mmH₂O.

In Experiment II, ^99mTc-DTPA (lmCi) was ad-ministered intrathecally through the cisterna magna and the changes in radioactivity were measured with the samples of venous blood and CSF, as well as of lymphatic fluid, every 30 minutes through the experiment. ICP was controlled by cisternal infusion at the same pressure levels as those in Experiment I. In contrast to the constant RI levels in cervical lymphatic fluid at normal pressure state, radioactivity in both lymphatic fluid and venous blood consistently increased during the periods of 30 to 210 minutes in the condition of raised ICP. In addition, radioactivity ratio of cervical lymphatic fluid to systematic venous blood also elevated in proportion to the loaded ICP levels and experi-mental time courses.

From these results, it is concluded that a part of CSF can be shifted into lymphatic channels under the condition of increased ICP and that shifted fluid is mainly derived from CSF space. When ICP is raised, the above mentioned CSF absorption into lymphatic system may play an important role to get CSF out from the cranial cavity.