定位脳手術よりみた視床内髄板の機能解剖

FUNCTIONAL ANATOMY OF THE INTERNAL MEDULLARY LAMINA BASED ON THE RESULTS OF STEREOTAXIC SURGERY

Ｉ．はじめに

　いわゆる頑痛症に対しては種々の外科的治療が試みられてきた。著者らの教室ではThalamolaminotomyすなわち定位的視床内髄板破壊術^52）により除痛を行つてきた。その根拠となる理論は，視床における痛みの中継核として二つの部位が想定される。一つは痛みの内proto—pathicな部分をうける非特殊感覚核の内髄板（すなわち広義の髄板内核--n．centralis lateralis （CL），　centremédian （Ce又はCM），　n．　parafascicularis （Pf），　n．　li—mitansなど）であり，他は痛みのうちepicriticな部分を中継する特殊感覚核のventrobasal complex （V．　B．）である。この両者は互に密接な関係にあり，前者は，後者に対し促通的に，後者は前者に対し抑制的に働いていると考えられる^21）。従つて痛みをとるためには，非特殊核である内髄板を破壊する^20）と同時にこの二つの中継核間にあると考えられる反響回路を絶つことが必要であるという^51）。

　このThalamolaminotomyの対象となる頑痛には癌による痛み，視床痛・神経痛，種々の原因による中枢痛等があり，必ずしも一定した効果が得られるとは限らない。第1表は手術直後と3ヶ月後の効果を調べたもので，全く痛みのとれた例もあるが部分的に痛みが残つたり，再発するものがある。例えば癌による痛みはその性質上，痛みの範囲が広がつたり，再発してくることがある。視床痛にも有効であるが痛みの性質に変化がみられるにすぎないか，あるいは何とも表現できないようなdysesthesiaが残つたりする場合もある。原因のはつきりしない，いわゆる中枢痛では，特に効果が一定しなかつたり，精神的な影響を多分にうける症例がみられる。

1) Cases of intractable pain treated by stereotaxic lesion of the internal medullary lamina of the thalamus (Thalamolaminotomy) were followed up. In 4 autopsy cases the thalamolaminotomy lesions corresponded correctly with the target checked by X-P according to Schaltenbrand-Bailey atlas. But the degree of the dilatation of the third ventricle must be taken into consideration for the mesure-ment of lateral distance from the midline. Effect of the relief of pain was better in the cases with bilateral large lesions of the internal medullary lamina including Centrum-medianum Parafascicular complex (CM-Pf) (Namely thalamolaminotomy) than those with the lesion only in the CM-Pf or Pf.

2) Degenerating fibers from the lesions were studied by Nauta-Gygax method. In all cases terminal degenerations are found in the specific nucleus of the thalamus, namely nucleus Ventro-caudalis parvocellularis (Vc. pc.). Some other de-generated fibers were seen in the IV-VI layers of the second sensory cortex.

3) The neurons which responded to the pin prick stimulation on almost all over the body were found in Pf. nucleus of the thalamus. Evoked responses were recorded on the second sensory cortex by electrical stimulation of CM. nucleus in the inter-nal medullary lamina. Evoked potentials were also obtained in the area of hand representation of the second sensory cortex by the stimulation of the contra-and ipsilateral median nerves. In this area single neurons, which responded to the same stimu-lation with the latency of about 45 msec were found. In one case of pharyngeal cancer, ablation of the contralateral second sensory cortex was effective for relief of pain.

4) It may be supposed that the internal medullary lamina of the thalamus relays a part of the pain impulses and in turn it has also some influences on the specific sensory nucleus of the thalamus, which relays epicritic sensation.

These findings suggest that the internal medullary lamina has connections with the second sensory cortex not only via the specific nucleus of the thalamus but also direct projections to it.

The first and second sensory cortex also seem to have regulatory activity on the specific and non-specific nuclei of the thalamus and the reticular formation of the brain stem.

Effective treatment for relief of pain must include large destruction of the bilateral internal medullary lamina. And corticectomy of the second sensoryarea may be also effective in some cases.