SOME COMMENTS ON THE PYRAMIDAL TRACT, WITH SPECIAL REFERENCE TO ITS INDIVIDUAL VARIATIONS IN MAN

Abstract

It has for a long time been generally accepted that a lesion of the pyramidal tract usually results in a spastic hemiplegia, characterized by impairment of skilled voluntary movements, increased myotatic (deep or tendon) rcflcxes, and weakened or abolished cutaneous reflexes with an extensor plantar response. However, after sectioning the middle third of the ccrebral peduncle in man containing the pyramidal tract fibres scvcral authors have reported that there is no, or only a slight and transient, spasticity and that the capacity to perform skilled voluntary moverncnts is only nioderately impaired ( WaIker 1849, W h i f e 1050, Bzicy 1857, Bucy & Keplinger 1961). These observations lctl Rucy to ask “Is there a pyramidal tract?”, and to suggest that cortical impulscs responsible for the production of skilled voluntary movements might take an “extrapyramidal” routc. Although symptomatological variations which may be seen following lesions supposed to involve the pyramidal tract infantile hemiplegia included may be due to concomitant damage to “extrapyramidal” structures, a problem to which we will briefly return in the final section of this paper, the question has often been raised whether such variations are due to a greater or lesser extent to individual morphological variations of the pyramidal tract. The chief purpose of the present paper is to review what is known of individual variations of this fibre system in man with regard to the following items : decussation of fibres, aberrant fibres, number and size of fibres and myelination of fibres. For a proper discussion of this, certain relevant data on the anatomy of the pyramidal tract have to be considered as well. Only few systematical studies on the individual variations of this fibre system in man have, however, been made. The data on which this review is based are, therefore, largely collcctcd from clinical case reports in the literature. Where it is relevant, data from other species will be considered.