[Congenital defects of the spinal part of the neural tube]

Abstract

The abnormal closure of the neural tube results in defects of the nervous system development, which are referred to as dysraphism. Considering successive steps of the development of the human foetus, it can be estimated that spinal cord malformations arise from pathologies of early foetal development between 17th and 28th day gestational age. This time period comprises a development of the neural plate and subsequently neural tube. The development is completed with a closure of a posterior aperture of the neural tube (caudal neuropore). Congenital malformations are often caused by defective closure of the caudal neuropore. The neural plate develops about 17th day gestational age, the cerebral vesicle appears about 21st day and the neural tube forms between 17th and 20th day. The rostral neuropore closes on the day 25th as does the caudal neuropore on the day 28th. The embryo is 2.5 mm long at the time. Noxious factors acting during that period can affect normal closure of the caudal neuropore and distort the process of spinal cord canalization. The resultant defect is called spina bifida. This is the most severe form of dysraphism-rachischisis. Meninges are also affected in this defect. They cannot cover the neural canal and on the margins of the lesion are replaced by epithelium. In milder types of the defect lack of a complete bony framework is concealed by soft tissues, forming a sac of variable size over the lesion. Spina bifida can be subdivided according to the sac structure: meningocoele, meningocysticoele, meningomyelocoele, meningomyelocystocoele. Central canal pathologies constitute another form of spinal cord malformations presenting as hydromyelia. Abnormal closure of the neural tube may affect development of the vertebral column and spinal cord along their entire length or only at a certain portion. Malformations are seen most frequently in the lumbo-sacral and then cervical regions.