First, posterior cranial fossa decompression Posterior cranial fossa decompression has a therapeutic effect on the disease is a relatively unanimous view, a large number of follow-up studies that the posterior cranial fossa decompression is accompanied by an improvement in clinical symptoms and the collapse of the cavity on the image or the diameter of the reduction of the MRI cerebrospinal fluid hydrodynamic studies have also confirmed that the occipital pool of the flow of the cerebrospinal fluid has improved significantly, although a small number of patients are not satisfied with the recovery, but in general, its long-term efficacy is certain. The long-term efficacy of the treatment is generally positive. (1) Expanded decompression (1) Post-occipital median incision, exposure of the occipital scales, C1 ~ C2, bite off the occipital scales 5 cm × 7 cm and the posterior arch of the C1. The width of the posterior border of the foramen magnum and the posterior atlantoaxial arch was not more than 2.5 cm, but it was easy to prolapse the cerebellum, forming pseudoexpansion and pulling on the midbrain. (2) Small-scale decompression of the posterior cranial fossa In response to the above drawbacks, many scholars bite off the occipital scales of the posterior cranial fossa decompression of 3cm × 4cm can also achieve good results, the focus of the operation should be on how to establish a smooth cerebrospinal fluid circulation pathway (eg, open the dura mater, cerebellar tonsillectomy to release the arachnoid adherence, etc.). (3) Expansion and repair of the skull Expansion and repair of the posterior cranial fossa after bony decompression of the squamous part of the occipital bone, including autologous bone grafting or the use of artificial repair materials (methyl methacrylate, titanium plate, etc.), the results are satisfactory. Although the scope of the posterior cranial fossa bony decompression is still controversial, the procedure is ideal to solve the congenital bony posterior cranial fossa volume reduction of Chiari malformation from the root, so as to make it conform to the physiological shape. Dural decompression There are different opinions on whether to open the dura mater and whether the dura mater should be expanded for repair. (1) Open dura refers to cutting the dura of the posterior cranial fossa without suturing, and only tightly suturing the muscle and subcutaneous layers after biting off the skull according to one of the above methods. Because of the many postoperative complications. It has been basically not used. (2) For infants and young children, due to better durability than adults, simple posterior cranial fossa bony decompression without dural repair can still achieve good results. (3) Expanded dural repair refers to the use of autologous fascia or artificial dura to expand the dura of the posterior cranial fossa in order to enlarge the volume of the posterior cranial fossa after cutting the dura mater in the shape of “Y”. The large-scale decompression of the posterior cranial fossa is associated with a high incidence of complications, and it is necessary to relieve the cerebellar tonsils of the extrusion of the medulla oblongata and the adhesion between them, emphasizing the importance of cerebellar tonsillectomy to improve the therapeutic effect. 1.Cerebellar tonsillectomy After craniotomy and cutting open the dura mater, the arachnoid membrane was further cut open, and the cerebellar tonsils herniated into the occipital foramen were removed by suction under the perichondrium without blood, so as to make them retract and lift the compression on the medulla oblongata. 2.Fourth ventricle output tract unblocking surgery The previous steps of this method are the same as cerebellar tonsil excision, and further microscopic separation of the herniated cerebellar tonsils and the adhesion of the brainstem and excision, probe the central canal opening of the spinal cord, and loosen the thickening of arachnoid membrane, so as to make the cerebrospinal fluid circulation of the fourth ventricle unobstructed. This procedure relieves the cause of spinal cord cavern from the pathogenesis, solves the obstacle of cerebrospinal fluid circulation at the occipital foramen, restores the physiological circulation of cerebrospinal fluid, and improves the cerebrospinal fluid dynamics. It should be a necessary step in the surgical treatment of Chiari malformation combined with spinal cord cavern.