ANATOMIC PATHWAYS RELATED TO IN FACE AND NECK*

JAMES A. TAREN, M.D., AND EDGAR A. KAHN, M.D. Section of Neurosurgery, Department of Surgery, University of Michigan Hospital, Ann Arbor, Michigan

(Received for publication May 19, 1961)

HE remarkable ability of the higher V is most dorsal in the tract. Fig. 4 is a dia- portions of the central nervous system gram of the medulla 6 mm. below the T to readjust to surgical lesions presup- which we believe to be the optimal level for poses the existence of alternate pathways. tractotomy. The operation is done with the This hypothesis has been tested with regard patient in the sitting position to facilitate to a specific localized sensory input, pain exposure. The medullary incision, 4-5 mm. from the face. in depth, extends from the bulbar accessory Our method has been to study the degen- rootlet to a line extrapolated from the pos- eration of nerve fibers by Weil and Marchi terior rootlets of the ~ud cervical nerve root. techniques following various surgical lesions An adequate incision results in complete in man and monkey. The lesions have con- analgesia of all 8 divisions as well as analgesia sisted of total and selective retrogasserian in the distribution of VII, IX, and X except rhizotomy in 3 humans and 3 monkeys, for sparing of the vermilion border of the lips medullary tractotomy in ~ humans and (Fig. 5). A degree of ataxia of the ipsilateral monkeys, and extirpation of the cervical upper extremity usually accompanies effec- portion of the nucleus of the descending tract tive tractotomy and is caused by compromise of V in ~ monkeys. The findings were dupli- of the cuneate and the spinocerebellar sys- cated in all. tems. Too anterior an incision into the al- Degeneration in the descending tract of V ready crossed lateral spinothalamic and ven- following selective retrogasserian rhizotomy tral secondary ascending tract of V may in man and monkey confirms that portions of produce analgesia on the contralateral body all 3 divisions of the trigeminal nerve are and face. Our failure in the past to eliminate represented as far caudally as C4 and that the mandibular, the maxillary, and the ophthalmic divisions have an essentially dorsal to ventral arrangement, respec- tively. 1,4,6 Fig. 1 is a diagram of the first- order neuron for pain and temperature from the face, the descending tract of V, and shows that the most central areas of the face terminate highest on the pars caudalis of the nucleus of the descending tract of V while the most peripheral areas of the face end lowest. Fig. ~ depicts the descending tract of V at various levels. Fig. 3 shows that mandibular

* Presented at meeting of the Harvey Cushing So- ciety, Mexico City, Mexico, April 19, 1961. A part of this work was carried out in tile Correlative FIG. 1. Diagram of the origins and terminations of the Neurosurgery Research Unit under U.S.P.tI.S. Grant descending tract of V. The fibers shown are those carry- B-144~(C3). ing impulses of pain and temperature. 116 ANATOMI(" PATHWAYS RELATED TO PAIN IN FACE AND NECK 117 mandibular-division pain was the result of an incision that was not dorsal enough in ex- tent. As further evidence for this latter point we cite a case in which medullary tractotomy 6 mm. below the obex spared the entire mandibular division. Revision of the tractot- omy by extending the incision 1-e rain. dorsally resulted in analgesia of all 3 divisions of V except for sparing of the vermilion bor- der of the lips. Fig. 6 is a diagram ot the usual secondary pathways mediating impulses from pain stimulation of the face or of the eervieal region to the posterior ventral thalamie nucleus. The ventral secondary ascending tract of V subserves the former and the

FIG, 3. Cross sections of inedulla of monkey stained by technique of Well. (A) Total degeneration in the de- seen(ling tract of V at level of sensory decussation fol- lowing total retrogasscrian rhizotomy. Note position of the dorsal superficial to the de- scending tract of V and the bulbar accessory rootlet which serves as a landmark for the anterior extent of the traetotomy incision. (B) Level of beginning motor dccussation showing degeneration in descending tract of V following retrogasserian rhizotoiny of mandibular filters only. Note dorsal location of the degeneration and its proximity to fasciculus cuneatus.

lateral spincthalamie tract the latter. The nucleus of the spinal tract of V is overlapped by the dorsal-horn gray; consequently the cell bodies of origin of the second-order neurons of these two tracts are in proximity. Each tract has a specific termination in the where synapses occur and third- order neurons ascend to a specific area of the somesthetic cortex. ~ Degeneration in the ventral secondary ascending tract of V produced by incision into, or excision of, the cervical part of the FIG. ~, Cross sections of stem after total retrogasserian rhizotomy to show the descending tract nucleus of the spinal tract of V shows that of V. (A) The level of cranial nerve XII. (B) A level 6 this ascending tract swings forward to cross ram. below the obex at sensory decussation which we chiefly at medullary levels rather than at the believe to be the optimal site for medullary tractotomy. Note position of the dorsal spinoeerebellar tract super- level of origin of the tract. Fig. 7 from a ficial to tim descending tract of V at this leveh human medullary tractotomy shows the