Sensory consequences of commissural myelotomy. A challenge to traditional anatomical concepts

Twenty-five cases of commissural myelotomy were studied. Representative cases are reported, including a histological examination of the lesion in one. Although the purpose of the operation is to produce a cuirass of loss of pain sensibility by dividing the spinothalamic and spinoreticulothalamic fibres as they decussate in the anterior commissure of the cord, this result is not always obtained. Whether or not the expected sensory loss is obtained, the chronic pain for which the operation is performed can be relieved. Sensibility tends to return towards normal after myelotomy. Even with substantial recovery of sensory loss, the pain for which the operation was performed can remain absent. Asymmetrical sensory loss may be produced by the operation; reasons for this are suggested. Differences between the results of commissural myelotomy and anterolateral cordotomy are discussed. Unlike the results of anterolateral cordotomy, which can be accounted for on the basis of known anatomy, the results of commissural myelotomy are inexplicable on present anatomical knowledge. Attention is drawn to the results of myelotomy reported originally by Hitchcock and confirmed by other neurosurgeons in which a short myelotomy incision in the upper cervical cord caused loss of pain over a vast region of the body. The difficulty in explaining the patterns of sensory loss in these cases is discussed. The literature on pathways alternative to the spinothalamic and spinoreticulothalamic is reviewed. It is argued that the central incision cannot cause relief of pain merely by cutting an afferent pathway, and it is suggested that this lesion blocks impulses entering into, in, or leaving the spinothalamic complex. The accurate localization of pinprick and thermal stimuli via the spinothalamic tract is demonstrated.