Stereotactic mesencephalotomy.

Within the mesencephalon lie nuclear masses and fiber tracts that connect higher and lower portions of the neuraxis. The pathways subserving epicritic (discriminatory) sensation and protopathic (motivational) sensation are adjacent to one another and can be localized precisely with stereotaxy. Discrete thermal lesions overflowing between the direct spinothalamic and quintothalamic pathways laterally and the more diffuse ascending pathways medially can be created. By careful target selection the surgeon can avoid significant damage to adjacent structures and offer relief of central or malignant pain without substantial sensory disturbance. At the same time the emotional disturbances that often persist with other remedies are reduced. Intraoperative electrophysiologic monitoring may help minimize unwanted and distressing side effects. It is fortunate that nature has designed the upper brain stem in such a fashion to allow effective pain relief procedures. Although stereotactic mesencephalotomy is not a panacea, it offers relief of pain syndromes that cannot otherwise be helped while abolishing the associated emotional problems that otherwise can be relieved only by psychosurgical procedures.