Patient, Ren, 70 years old. Numbness and weakness of the left half of the body for 1 year dizziness with dysphagia for 2 months. At the time of admission, the patient was examined: clear consciousness, fluent speech, bilateral pupils dilated and equidistant, eyeballs moving freely to all sides, no nystagmus. There was no nystagmus. There was no superficial sensory loss on the left side of the face, superficial sensory loss on the left side of the body, muscle strength of the left side of the upper and lower limbs was reduced (grade 4), bilateral knee tendon reflexes were basically normal, and no pathological signs were elicited. Magnetic resonance examination: the cerebellar tonsils were seen to be located about 15 mm or more below the foramen magnum of the occipital bone, and no tubular cavities were seen in the spinal cord. Cranial CT examination showed left thalamic infarction and normal ventricular system. Suboccipital cranial and posterior arch of atlantoaxial vertebrae (2cm) resection and dural enlargement and repair were given, and the patient’s choking on drinking water and dysphagia disappeared after the operation.