Subhypophyseal tonsillar herniation malformation, also known as ArnoldCChiari malformation, is a common congenital developmental anomaly. In severe cases, part of the lower part of the medulla oblongata and the lower earthworm of the lower part of the four ventricles also herniates into the spinal canal. It is often combined with a spinal cord cavity, which can also cause cerebrospinal fluid circulation obstruction and hydrocephalus. Submural herniation of the cerebellum is often associated with other craniocervical malformations such as cervical spina bifida and cerebellar hypoplasia. It may manifest as headache, weakness of the upper limbs of the head and face, loss of pain and warmth in the shoulder and arm, difficulty in swallowing, vertigo, nausea, ataxia, and even paralysis. The disease was first proposed by Austrian pathologist HansChiari at the end of the 19th century and later added by other scholars, and is divided into four types, mostly type 1 or type 2. Type I is the one with the mildest clinical manifestations. It is also called primary cerebellar heterotopia, which is characterized by subungual herniation of the cerebellar tonsils below the level of the foramen magnum and into the spinal canal, with a mild downward displacement of the medulla oblongata and a normal position of the fourth ventricle. It is often associated with cervical spinal cord cavitation and craniocervical bone deformity. Type II not only has herniation of the cerebellar tonsils (with or without the earthworm) into the spinal canal, but also has subluxation of the pontine brain, medulla oblongata, and fourth ventricle, with “kink-like flexion and deformation” of the normal cervical junction, incomplete development of certain structures such as the skull, dura mater, midbrain, and cerebellum, etc. 90% of them have hydrocephalus, and are often combined with spinal cord cavitation, abnormal neuronal migration, and spinal cord spinal membrane The spinal cord is often combined with cavernous spinal cord, abnormal neuronal migration, and spinal cord spinal membrane bulge. Type III is the most severe type and is rare. It presents with herniation of the medulla oblongata, cerebellar earth, four ventricles and part of the cerebellar hemispheres into the upper part of the vertebral canal, combined with abnormal development of the occipital bone, occipital meningoencephalomegaly, spinal cord cavitation and embolism, and obvious head and neck deformity, cerebellar malformation, etc. Type IV, with significant cerebellar and brainstem hypoplasia, but without herniation into the spinal canal, often dies in the neonatal period. Scholars differ in their opinions about the pathogenesis. Among them, the traction theory is the most popular view, which believes that in patients with spina bifida and spinal cord spondylolisthesis, the spinal cord is fixed at the spina bifida, and in the process of growth and development, the spinal column and spinal cord grow at different rates, and the spinal cord cannot move up according to the normal situation, causing the spinal cord and cerebellar tissue to move downward, resulting in subungual herniation of the cerebellar tonsils. Some scholars also believe that the spinal cord is affected by the pull is mainly confined to the lumbosacral region, the thoracic segment is rarely involved, while the patients with spinal cord embolism syndrome do not all have a combination of cerebellar subm tonsillar herniation deformity, so it is believed that spinal cord spinal herniation is not related to the cerebellar subm tonsillar herniation, but the primary deformity of the medulla oblongata, cerebellum, spinal cord occipital and brain, in the development process, the posterior cranial fossa volume is small, brain tissue overgrowth so that part of the brain, linguopharyngeal The posterior group of cerebral nerves and deep cervical nerve roots are pulled down, the foramen magnum and the superior cervical canal are filled, and cerebrospinal fluid circulation is obstructed, secondary to hydrocephalus. The disease is often associated with other craniocervical malformations such as spinal cord spinal bulge and tissue herniation out of the foramen magnum. In severe cases, the medulla oblongata may be completely displaced outside the foramen magnum. This results in dorsal flexion of the medulla oblongata, compression and flattening of the cerebral nerve and cervical nerve, adhesion of the herniated brain tissue to the spinal cord and surrounding structures, occlusion of the foramen magnum, adhesion and occlusion of the middle cerebral canal or the foramen magnum of the fourth ventricle, formation of obstructive hydrocephalus, which may aggravate the herniation of the medulla oblongata. Occlusion of the median foramen may be accompanied by spinal cord cavitation or other occipital foramen malformations. The theory of hydrocephalus has also been proposed, suggesting that subcerebellar tonsillar herniation is due to downward pressure of hydrocephalus in infants. In severe cases, it herniates into the spinal canal of the upper cervical region, with the medulla oblongata and the fourth ventricle extending downward at the same time. In severe cases, the medulla oblongata is herniated into the spinal canal of the upper cervical segment, and the medulla oblongata and the fourth ventricle are herniated downward at the same time. The cerebellar tonsils often fill the medullary pool of the cerebellum, with tissue adhesions in this area, and the subarachnoid space is occluded, sometimes forming cysts; due to occlusion of the medullary pool of the cerebellum, adhesions of the middle foramen of the fourth ventricle, or adhesions of the middle cerebral aqueduct can cause obstructive hydrocephalus; the medulla oblongata and the superior cervical medulla are distorted by compression, the cervical medulla is displaced downward, the cerebellum is subluxated, the cerebral nerves are elongated, and the superior cervical nerves enter the intervertebral foramen in an external superior direction; there may be a midbrain The cerebellum may be subluxated, and the lateral pontine pool and cricoid pool may be occluded. The onset of submicrocephalic herniation malformation is slow, with more women than men; age ranges from 13 to 68 years, with an average of 38 years. Type I is most common in children and adults, type II in infants, type III in the neonatal period, and type IV often develops in infancy. The most common symptom of the malformation is pain, usually in the occipital, neck and arm areas, with burning radiating pain, rarely localized pain usually persistent, and pain that worsens with neck movement. Other symptoms include vertigo, tinnitus, diplopia, unsteadiness in walking and muscle weakness. Type I may be clinically asymptomatic or have mild posterior group cerebral and spinal nerve symptoms. Type II is often clinically associated with lower extremity motor and sensory deficits and cerebellar symptoms. Type III is mostly seen in infants and newborns, and often has lower limb motor and sensory deficits and symptoms of hydrocephalus brainstem and spinal cord compression, and cerebellar symptoms. Common signs include hyperreflexia of the lower limbs and muscle atrophy of the upper limbs. Most patients have sensory disturbances, often with hyperalgesia in the upper extremities and hypoesthesia in the lower extremities. Nystagmus is common, with an occurrence rate of 43%. Weakness of the soft palate with choking is common. Optic disc edema is rare, while those with optic disc edema are most often associated with cerebellar or pontine tumors. According to the age of onset, clinical manifestations and auxiliary examinations, the diagnosis of submicrocephalic tonsillar herniation malformation is generally not difficult. MRI examination of the head and neck, especially sagittal images, can clearly show the degree of submicrocephalic tonsillar herniation, as well as secondary hydrocephalus and spinal cord cavitation, which is an important basis for diagnosis. 1.Cranial spine plain film The skull and cranial spine planes can show their combined bony deformities, such as basal recess, atlanto-occipital fusion, spina bifida, and Klippel-Feil syndrome. 2.CT scan CT scan is mainly used to show various pathological changes by vertebral canal and brain pool imaging and combined with coronal scanning and sagittal reconstruction techniques. Type I: CT shows the following: ①The cerebellar tonsils are displaced downward and herniated into the vertebral canal to varying degrees, and the axial image shows two ovoid soft tissue masses on the dorsolateral side of the spinal cord at the upper end of the vertebral canal, which continues upward with the cerebellum. The cerebral pool angiogram with coronal view shows more clearly. However, it should be noted that the cerebellar tonsils are still within the normal range within 3 mm below the greater occipital foramen, between 3 and 5 mm is a borderline abnormality, and above 5 mm is a pathological state. ②The position of the medulla oblongata and the fourth ventricle is normal, but the fourth ventricle may be prolonged. ③It may be accompanied by hydrocephalus (0%-40%). ④It is often combined with spinal cord cavitation, etc. About 1/3 to 1/2 patients have cranio-spinal fusion deformity. Type II: In addition to the manifestations of type I, there are also changes in the skull, dura mater, cerebral ventricles and pools on CT. Cranial and dural changes: skull cap fractures are seen at birth and disappear 2-4 weeks or months after birth. The cerebellum grows in the narrow posterior cranial fossa, so that it compresses and erodes the slope and the temporal bone rock. In mild cases, the posterior edge of the rock becomes flat or depressed, and the internal auditory canal becomes shorter. The falx cerebri is hypoplastic or perforated, and the anterior middle 2/3 of the brain is most susceptible to involvement. Axial and coronal enhancement scans do not show complete linear strengthening of the falx or interrupted linear strengthening. The cerebellar curtain is attached near the greater occipital foramen, making the posterior cranial fossa even narrower. The foramen cerebellaris is enlarged and loses its normal “V” shape and forms a “U” shape. The main treatment for subungual herniation of the cerebellum is surgery. The purpose of surgery is to relieve the compression of the cerebellum, brainstem spinal cord, fourth ventricle and other neurological structures in the area by the foramen magnum and superior cervical spine, to separate the arachnoid adhesions of the median foramen of the occipital pool and superior cervical medulla to the extent possible, to relieve neurological symptoms and to relieve hydrocephalus. Patients with obstructive hydrocephalus or increased cranial pressure, significant neurological symptoms such as laryngeal tinnitus, apnea, cyanotic episodes due to brainstem compression, Homer’s syndrome of coracoacusis, loss of gag reflex and cerebellar dysfunction should be treated surgically. Surgical options include suboccipital craniotomy and decompression of the upper cervical lamina or cerebrospinal fluid shunt. It is believed that suboccipital decompression is feasible for type I, while type II can be treated by shunting only. In general, a full decompression of the posterior cranial fossa is performed by removing part of the occipital bone and the 1st or 2nd cervical vertebral plate, cutting the dura and separating the adhesions, and exploring the median foramen of the 4th ventricle. Patients who meet the indications for surgery should undergo surgery early. Surgical treatment is most effective within 2 years of the onset of symptoms, and pain can often be relieved postoperatively, while limb weakness is not easily improved, especially in those with muscle atrophy; the improvement rate of spinal cord cavity imaging can be as high as 90% or more, and the associated symptom relief rate can be 60-70%.