ten Donkelaar H J, Lammens M, Wesseling P, Hori A, Keyser A, Rotteveel J
Department of Neurology, University Medical Centre Nijmegen, P. O. Box 9101, 6500 HB Nijmegen, The Netherlands.
J Neurol. 2004 Dec;251(12):1429-42. doi: 10.1007/s00415-004-0653-3.
The corticospinal tract develops over a rather long period of time, during which malformations involving this main central motor pathway may occur. In rodents, the spinal outgrowth of the corticospinal tract occurs entirely postnatally, but in primates largely prenatally. In mice, an increasing number of genes have been found to play a role during the development of the pyramidal tract. In experimentally studied mammals, initially a much larger part of the cerebral cortex sends axons to the spinal cord, and the site of termination of corticospinal fibers in the spinal grey matter is much more extensive than in adult animals. Selective elimination of the transient corticospinal projections yields the mature projections functionally appropriate for the pyramidal tract. Direct corticomotoneuronal projections arise as the latest components of the corticospinal system. The subsequent myelination of the pyramidal tract is a slow process, taking place over a considerable period of time. Available data suggest that in man the pyramidal tract develops in a similar way. Several variations in the funicular trajectory of the human pyramidal tract have been described in otherwise normally developed cases, the most obvious being those with uncrossed pyramidal tracts. A survey of the neuropathological and clinical literature, illustrated with autopsy cases, reveals that the pyramidal tract may be involved in a large number of developmental disorders. Most of these malformations form part of a broad spectrum, ranging from disorders of patterning, neurogenesis and neuronal migration of the cerebral cortex to hypoxic-ischemic injury of the white matter. In some cases, pyramidal tract malformations may be due to abnormal axon guidance mechanisms. The molecular nature of such disorders is only beginning to be revealed.
皮质脊髓束在相当长的一段时间内发育，在此期间可能会发生涉及这条主要中枢运动通路的畸形。在啮齿动物中，皮质脊髓束的脊髓生长完全在出生后发生，但在灵长类动物中很大程度上在出生前发生。在小鼠中，已发现越来越多的基因在锥体束发育过程中发挥作用。在实验研究的哺乳动物中，最初大脑皮层有大得多的部分向脊髓发送轴突，并且皮质脊髓纤维在脊髓灰质中的终止部位比成年动物广泛得多。选择性消除短暂的皮质脊髓投射会产生功能上适合锥体束的成熟投射。直接的皮质运动神经元投射作为皮质脊髓系统的最新组成部分出现。随后锥体束的髓鞘形成是一个缓慢的过程，需要相当长的时间。现有数据表明，人类的锥体束以类似的方式发育。在其他方面正常发育的病例中，已经描述了人类锥体束在索状走行上的几种变异，最明显的是那些锥体束未交叉的情况。一项以尸检病例为例的神经病理学和临床文献调查表明，锥体束可能参与大量发育障碍。这些畸形大多是广泛谱系的一部分，范围从大脑皮层的模式形成、神经发生和神经元迁移障碍到白质的缺氧缺血性损伤。在某些情况下，锥体束畸形可能是由于轴突导向机制异常。此类疾病的分子本质才刚刚开始被揭示。
