FACIAL pain persisting not only after application of the usual conservative methods of treatment but also after neurosurgical procedures such as retrogasserian rhizotomy and/or prefrontal lobotomy is a challenging problem.We had the opportunity to make observations in six cases of this type in which we placed electrolytic lesions in the pain-conducting pathways at the mesencephalic level by means of the stereoencephalotome (mesencephalotomy). In some cases this procedure was combined with lesions of the dorsomedial nuclei of the thalamus (mesencephalothalamotomy1) in order to reduce the emotional reactivity to remaining pain sensation due to accessory pain-conducting fibers.TECHNICAL AND ANATOMICAL DATA Originally the punctures were performed through the superior colliculi at the level of the pineal center, or a few millimeters behind this point, in a direction parallel to the interaural plane. Recently we have chosen an oblique puncture which is inclined backward 34 degrees to the interaural plane2 and which lies in a plane through the posterior commissure. This oblique direction of the puncture increases the probability of injuring the ascending painconducting pathways.Since we found in measurements on 30 brains 3 that the interaural line2 intersects the posterior commissure-pons line 2 at an average angle of inclination 2 of -gA degrees, a puncture at an angle of +34 degrees corresponds to a section cut at right angles tó the midsagittal plane at an angle of +30 degrees to the posterior commissure-pons line ( Fig. 1 ; line B, Fig. 3). The From the
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