Chiari malformation (Arnold-Chiari syndrome) is a disease in which the brain structures located in the posterior cranial fossa are lowered in the caudal direction and exit through the large occipital foramen. Depending on the type, Chiari malformation can manifest itself as headache in the back of the head, pain in the cervical region, dizziness, nystagmus, fainting, dysarthria, cerebellar ataxia, laryngeal paresis, hearing loss and ear noise, visual impairment, dysphagia, respiratory apnea, stridor, sensitivity disorders, muscle hypotrophy and tetraparesis. Disease is diagnosed by brain MRI, cervical and thoracic spine. Chiari malformation, accompanied by persistent pain syndrome or neurological deficiency, is subject to surgical treatment (decompression of the posterior cranial fossa or bypass surgery).
Q07.0 Arnold-Chiari syndrome
In the area of the connection of the skull with the vertebral column there is a large occipital foramen, at the level of which the brain stem passes into the spinal cord. Above this hole, the posterior cranial fossa is localized. It contains the bridge, the medulla oblongata and the cerebellum. Chiari malformation is associated with the exit of part of the anatomical structures of the posterior cranial fossa into the lumen of the large occipital foramen. In this case, compression of the structures of the medulla oblongata and spinal cord located in this area occurs, as well as a violation of the outflow of cerebrospinal fluid from the brain, leading to hydrocephalus. Together with platybasia, assimilation of Atlanta, etc. Chiari malformation refers to congenital malformations of the craniovertebral junction.
Chiari malformation occurs according to various data in 3-8 people per 100 thousand of the population. Depending on the type, Chiari malformation can be diagnosed in the first days after the birth of a child or become an unexpected find in an adult patient. In 80% of cases, Chiari malformation is combined with syringomyelia.
Until now, the Chiari malformation remains a disease, about the etiology of which there is no consensus in neurology. A number of authors believe that Chiari malformation is associated with a reduced size of the posterior cranial fossa, which leads to the fact that as the structures located in it grow, they begin to exit through the occipital foramen. Other researchers suggest that Chiari’s anomaly develops as a result of the increased size of the brain, which at the same time pushes the contents of the posterior cranial fossa through the occipital foramen.
Hydrocephalus can provoke the transition of a slightly pronounced anomaly into a pronounced clinical form, in which the total volume of the brain increases due to an increase in the ventricles. Since Chiari malformation, along with dysplasia of the bone structures of the craniovertebral junction, is accompanied by underdevelopment of the ligamentous apparatus of this area, any craniocerebral injury can lead to an aggravation of the insertion of the cerebellar tonsils into the occipital foramen with the manifestation of the clinical picture of the disease.
Chiari malformation is divided into 4 types:
- I is characterized by the lowering of the tonsils of the cerebellum below the large occipital foramen. It usually manifests itself in adolescents or in adulthood. Often accompanied by hydromyelia — accumulation of cerebrospinal fluid in the central canal of the spinal cord.
- II itself in the first days after birth. In addition to the tonsils of the cerebellum in this pathology, the cerebellar worm, the medulla oblongata and the IV ventricle also exit through the large occipital foramen. Chiari malformation type II is much more often combined with hydromyelia than the first type, and in the vast majority of cases is associated with myelomeningocele — congenital spinal hernia.
- III is distinguished by the fact that the cerebellum and the medulla oblongata, which descended through the large occipital foramen, are located in the meningocele of the cervical-occipital region.
- IV consists in hypoplasia (underdevelopment) of the cerebellum and is not accompanied by its displacement in the caudal direction. Some authors attribute this anomaly to the Dandy-Walker syndrome, in which cerebellar hypoplasia is combined with the presence of congenital cysts of the posterior cranial fossa and hydrocephalus.
Anomaly of Chiari II and Chiari III is often observed in combination with other dysplasias of the nervous system: heterotopia of the cerebral cortex, polymicrogyria, anomalies of the corpus callosum, cysts of the Mozhandi orifice, inflection of the sylvian aqueduct, hypoplasia of subcortical structures, namet and sickle of the cerebellum.
The most common type I occurs in clinical practice. It is manifested by cerebrospinal hypertension, cerebellobulbar and syringomyelic syndromes, as well as damage to the cranial nerves. Usually, the Chiari I anomaly manifests itself during puberty or already in adulthood.
The cerebrospinal hypertension syndrome, which is accompanied by type I, is characterized by headache in the back of the head and neck area, which increases during sneezing, coughing, straining or straining of the neck muscles. Vomiting may occur, regardless of the food intake and its nature. When examining patients with Chiari malformation, an increased tone of the neck muscles is detected. Among cerebellar disorders, speech disorders (dysarthria), nystagmus, cerebellar ataxia are observed.
Damage to the brain stem, the nuclei of cranial nerves located in it and their roots are manifested by a decrease in visual acuity, diplopia, swallowing disorder, hearing loss of the type of cochlear neuritis, systemic dizziness with the illusion of rotation of surrounding objects, ear noise, sleep apnea syndrome, recurrent short-term loss of consciousness, orthostatic collapse. Patients who have disease note an increase in dizziness and ear noise when turning their heads. Turning the head in such patients can provoke fainting. There may be atrophic changes in half of the tongue and laryngeal paresis, accompanied by hoarseness of voice and difficulty breathing. Tetraparesis is possible with a greater decrease in muscle strength in the upper extremities than in the lower ones.
In cases where type I is combined with syringomyelia, syringomyelic syndrome is observed: dissociated type sensitivity disorders, numbness, muscle hypotrophy, pelvic disorders, neuroarthropathy, disappearance of abdominal reflexes. At the same time, some authors point to the discrepancy between the size and location of the syringomyelic cyst, the prevalence of sensitivity disorders, the severity of paresis and muscular hypotrophy.
Type II and III anomalies have similar clinical manifestations that become noticeable from the first minutes of a child’s life. Chiari II anomaly is accompanied by noisy breathing (congenital stridor), periods of short-term respiratory arrest, bilateral neuropathic laryngeal paresis, swallowing disorders with liquid food thrown into the nose. In newborns, Chiari II anomaly is also manifested by nystagmus, increased muscle tone in the upper extremities, cyanosis of the skin that occurs during feeding. Motor disorders can be expressed to varying degrees and progress up to tetraplegia.Type III has a more severe course and is often an incompatible with life fetal development disorder.
Neurological examination and the standard list of neurological examinations (EEG, Echo-EG, REG) do not provide specific data to establish the diagnosis of “Chiari malformation”. As a rule, they reveal only signs of a significant increase in intracranial pressure, i.e. hydrocephalus. Skull x-ray reveals only bone anomalies, which may be accompanied by Chiari malformation. Therefore, before the introduction of tomographic research methods into neurological practice, the diagnosis of this disease presented great difficulties for a neurologist. Now doctors have the opportunity to give such patients an accurate diagnosis.
It should be noted that MSCT and CT brain with good visualization of the bone structures of the craniovertebral junction do not allow us to accurately judge the soft tissue formations of the posterior cranial fossa. Therefore, the only reliable method of diagnosing Chiari malformation today is magnetic resonance imaging. Its implementation requires immobility of the patient, therefore, in young children it is carried out in a state of drug-induced sleep. In addition to MRI of the brain to detect meningocele and syringomyelic cysts, it is also necessary to conduct an MRI spine, especially its cervical and thoracic sections. At the same time, MRI studies should be aimed not only at diagnosing Chiari malformation, but also at finding other abnormalities of the nervous system that are often combined with it.
Asymptomatic Chiari malformation does not need treatment. In cases where Chiari malformation is manifested only by the presence of pain in the neck and occipital region, conservative therapy is carried out, including analgesic, anti-inflammatory and muscle relaxant drugs. If Chiari malformation is accompanied by neurological disorders (paresis, disorders of sensitivity and muscle tone, disorders of the cranial nerves, etc.) or pain syndrome that does not respond to conservative therapy, then surgical treatment is indicated.
Craniovertebral decompression is most often used in the treatment of Chiari malformation. The operation includes the expansion of the occipital foramen by removing part of the occipital bone; the elimination of compression of the trunk and spinal cord by resection of the tonsils of the cerebellum and the posterior halves of the first two cervical vertebrae; normalization of the circulation of cerebrospinal fluid by sewing patches of artificial materials or allograft into the dura mater. In some cases, Chiari malformation is treated with shunting operations aimed at draining cerebrospinal fluid from the expanded central canal of the spinal cord. Cerebrospinal fluid can be discharged into the thoracic or abdominal cavity (lumboperitoneal drainage).
An important prognostic value is the type to which the Chiari malformation belongs. In some cases, Chiari I anomaly may remain asymptomatic throughout the patient’s life.Type III in most cases leads to a fatal outcome. With the appearance of neurological symptoms of Chiari I anomaly, as well as with Chiari II anomaly, timely surgical treatment is of great importance, since the neurological deficit that has arisen does not recover well even after a successful operation. According to various data, the effectiveness of surgical craniovertebral decompression is 50-85%.