1.Congenital developmental abnormality: subcerebellar tonsillar hernia, flat skull base, hydrocephalus, etc. are the most common causes. Abnormal cerebrospinal fluid dynamics: congenital occlusion at the exit of the fourth ventricle obstructs the normal circulation of cerebrospinal fluid, and the pressure is transmitted to the spinal cord, resulting in dilatation of the central canal of the spinal cord. Abnormal blood circulation: spinal cord vascular malformation, tumor cystic degeneration, inflammation, ischemia, necrosis and other causes of blood circulation disorders resulting in central canal softening and dilatation. Summarize: the first category of causes can often be relieved by surgical treatment, while other causes can be treated symptomatically.