Disease classification The disease was first proposed by the 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 type with the mildest clinical manifestations. It is also called primary cerebellar heterotopia, which manifests as 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 earthworms) into the vertebral canal, but also herniation of the pontine brain, medulla oblongata, and the 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 the cases 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 spinal cord cavitation, neuronal migration abnormalities, spinal cord spinal membrane bulge, etc. Wang Dianhong, Department of Neurosurgery, The First Hospital of Harbin Medical University 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 hemisphere into the upper part of the spinal canal, combined with abnormal occipital bone development, occipital meningeal brain expansion, spinal cord cavity 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. Etiology The pathogenesis of the disease has been the subject of different opinions. Among them, the traction theory is the most popular view. It is believed that in patients with spina bifida and spinal cord herniation, the spinal cord is fixed at the spina bifida, and during growth and development, the spinal column and spinal cord grow at different rates, and the spinal cord cannot move upward as normal, causing the spinal cord and cerebellar tissue to move downward, resulting in subungual herniation of the cerebellum. Some scholars also believe that the spinal cord is mainly limited to the lumbosacral region, the thoracic segment is rarely involved, while the patients with spinal cord embolism syndrome do not all have a combined subcerebellar tonsillar herniation deformity, so it is believed that spinal cord spinal herniation is not related to subcerebellar tonsillar herniation, but a 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, linguopharynx The posterior group of cerebral nerves and deep cervical nerve roots are pulled down, the foramen magnum and superior cervical spinal canal are filled, and cerebrospinal fluid circulation is obstructed, secondary to hydrocephalus. The disease is often associated with other craniocervical deformities 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 causes dorsal flexion of the medulla oblongata, the brain nerve and cervical nerve are pulled and the spinal cord is compressed and flattened, the herniated brain tissue adheres to the spinal cord and surrounding structures, the foramen magnum occludes, the middle cerebral aqueduct or the foramen magnum of the fourth ventricle adheres and occludes, forming 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 compression of hydrocephalus in infants. In severe cases, it herniates into the upper cervical spinal canal, with the medulla oblongata and the fourth ventricle extending downward at the same time. In severe cases, herniation of the medulla oblongata into the vertebral canal is accompanied by the extension of the medulla oblongata and the fourth ventricle downward. 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 a cyst; obstructive hydrocephalus may result from occlusion of the medullary pool of the cerebellum, adhesions to the middle foramen of the fourth ventricle, or adhesions to the middle cerebral aqueduct. The cerebellum may be subluxated, and the lateral pontine pool and cricoid pool may be occluded. The onset of subungual herniation of the cerebellum is slow, with more women than men; the 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 extremity 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 often associated with cerebellar or pontine tumors. Diagnosis 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 are important bases for diagnosis. 1.Cranial spine plain radiographs of the skull and cranial spine planes can show their combined bony deformities, such as basal sunkenness, atlanto-occipital fusion, spina bifida, and Klippel-Feil syndrome. 2.CT scan CT scan mainly shows various pathological changes by vertebral canal and brain pool imaging and combined with coronal scanning and sagittal reconstruction techniques. Type I: CT shows: 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, continuing upward with the cerebellum. The cerebral pool imaging is more clear with the coronal view. 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. The 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 cranial vertebral fusion deformity. Type II: In addition to the manifestations of type I, there are also changes in the skull, dura mater, ventricles and pools of the brain. Cranial and dural changes: skull cap fractures are seen at birth and disappear within 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. In severe cases, the foramen magnum is enlarged. Axial and coronal enhancement scans do not show complete linear strengthening of the falx or interrupted linear strengthening. The cerebellar curtain is attached to the greater occipital foramen, making the posterior cranial fossa more narrow. The foramen magnum is enlarged and loses its normal “V” shape and forms a “U” shape. Differential diagnosis The submicrocephalic tonsillar herniation deformity should be differentiated from intracranial occupying lesions causing herniation of the cerebellar tonsil foramen occipitalis: in the former, the tonsils are mostly tongue-shaped and often combined with other deformities, while in the latter, the tonsils are mostly conical and may be combined with signs of intracranial occupying lesions. 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 the superior cervical spine, to separate the arachnoid adhesions of the median foramen of the occipital pool and the 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 coracocephaly, 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. The prognosis of the disease Patients who are eligible for surgery should undergo surgery early. The best results of surgical treatment are achieved 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 remission rate of related symptoms can be 60-70%. Disease prevention The main focus is to pay attention to female pregnancy and perinatal health care to prevent disease and not to use drugs arbitrarily to prevent the birth of congenitally malformed children.