Arnold-Chiarimalformation, also known as Chiari malformation, is a congenital developmental abnormality in which the cerebellar tonsils extend downward, or the lower part of the medulla oblongata or even the Ⅳ ventricle, through the foramen magnum into the cervical spinal canal due to abnormal development of the brain structures in the posterior cranial sulcus during the embryonic period. The pathogenesis of the disease Currently, there are different opinions on the pathogenesis of the disease. It is mostly believed that the lower herniation is due to the overgrowth and extension of brain tissue in the midline structure of the posterior cranial recess during the embryonic period, which, together with the volume reduction of the posterior cranial recess, further encourages it to herniate downward into the cervical spinal canal through the foramen magnum. Some of them even descend to the cardinal vertebrae or lower, so as to seriously damage the cerebellum, brainstem and high cervical medulla and cervical nerve, and may cause hydrocephalus. The disease is often combined with other occipital deformities, such as skull base depression, atlanto-occipital fusion, flattened skull base, and cervical segmentation insufficiency. The clinical manifestations depend mainly on the presence or absence of concurrent spinal cavity, brainstem and cerebellar compression. Symptoms caused by subungual herniation of the cerebellum are generally as follows: 1. cranial and cervical nerve symptoms include hoarseness, dysphagia, neck pain, and limitation of movement. Brainstem medulla symptoms may include limb movement disorders, hemiparesis and quadriplegia, sensory disorders of the limbs, and urinary and fecal disorders. Cerebellar symptoms may include ataxia, unstable walking and nystagmus. 4. The symptoms of increased intracranial pressure may include headache, vomiting, and vision loss. 5, spinal cord cavitation symptoms with spinal cord cavitation may appear sensory separation or muscle atrophy of both upper limbs. Diagnosis MRI examination can clearly show the specific location of subungual herniation, the presence of medulla oblongata and subventricular herniation, the displacement of brainstem, the presence of spinal cord cavity and hydrocephalus, etc. X-ray plain film examination and CT can understand the bony deformity of the cranial neck. At present, we apply the international advanced cerebrospinal fluid film technology to understand the circulation of cerebrospinal fluid, so that the cause of cerebrospinal fluid circulation obstruction can be clarified before surgery. Based on the above clinical manifestations, combined with MRI examination, the diagnosis is not difficult to establish. Treatment General conservative treatment is not able to slow down the further development of the disease. Due to the loss of cerebrospinal fluid cushioning at the cervico-occipital junction, inadvertent injury to the neck may result in serious consequences such as limb paralysis, respiratory arrest or even death. Therefore, surgery can not only stop the further development of the disease, but also can fundamentally relieve the patient of the cause of the disease. Therefore, surgery is the first choice and the consensus among domestic and foreign neurosurgeons. surgery for Chiari malformation spinal cord cavity is aimed at relieving the compression of the medulla oblongata and/or superior cervical medulla by the inferior herniated cerebellar tonsils or the invaginated dentate process, which is the main purpose of surgery. Minimally invasive surgical treatment Minimally invasive small incisions (about 5-7 cm in length), application of minimally invasive instruments, and small bone windows (2X3 cm in size) have been used to treat subcerebellar tonsillar herniation with spinal cord cavity with good results. Minimally invasive surgery is completely different from conventional major surgery, as we perform various operations within the dura mater with the assistance of a microscope, such as separating the adhesions between the cerebellar tonsils and the brainstem and relieving the obstruction of the middle foramen of the fourth ventricle, with minimal possibility of damaging the surrounding vital structures during the surgery, and even less risk to life. We believe that microsurgery is the best option for submicrocephalic tonsillar herniation with spinal cord cavity, as the mortality rate of this procedure is 0.5 per 1,000.