Chiari malformation is a disease of central nervous system, which affects the position of the cerebellar tonsils. It was named after the Austrian scientist Hans Chiari, who described this condition in the 1891 (Schijman, 2004). The pathoanatomic basis of this disorder is the inferior position of the cerebellum and brainstem comparatively to the anatomic standard. In a healthy person, cerebellar tonsils are located above the foramen magnum in the postcranial fossa. Due to this disorder, they are dislocated to the level of the first or second vertebra. Normally cerebrospinal fluid is constantly circulating through the cavities in the brain. Most of it are produced in the lateral ventricles of the brain from where it passes to the third ventricle through the foramina of Monro. After that, it flows to the fourth ventricle through the cerebral aqueduct. Cerebrospinal fluid leaves the brain through the two foramina of Lushka and one foramen of Magendi, reaching the subarachnoid space. It is clear that the spinal canal is not adapted to any displacement of volumetric structures in it. Dislocated structures of the cerebellum obturate this limited space and therefore, the disease leads to increased intracranial pressure and the breach of natural cerebrospinal fluid outflow.
Malformation may be primary or secondary regarding its cause. Primary malformation occurs due to the congenital structural features of the skull. Patients with the Chiari malformation have much smaller posterior fossa (Furtado, Reddy, and Hegde, 2009). In turn, the cause of this cavity space decrease during the fetal development can be a lack of certain nutrients in the diet during pregnancy, genetic mutations or predisposition. Therefore, primary Chiari malformation type one is more common than secondary. However, it is generally asymptomatic and reveals itself during the periods of intense growth of the person in the late childhood or even in the adulthood. Secondary Chiari malformation affects people with no specific structural features of the skull structure. Its pathogenesis is associated with the volumetric formations in the skull such as hematomas, tumors. It may happen also due to the trauma. When the spinal canal becomes permeable to the cerebrospinal fluid as a result of its rupture, infection or toxic substances poisoning happens excessive spinocerebral fluid loss, which leads to the pseudo-Chiari malformation. Based on the severity of displacement, which is visualized by CT or MRI, Chiari malformation is divided into four types. Type one Chiari malformation is diagnosed when the only cerebellum is affected by the pathologic changes and the position of the brainstem remains unchanged. It is the least severe type regarding person health because it leads to lower mortality and disability rates.
As the leading disease syndrome is an obstruction of the outflow of cerebrospinal fluid, development of disorders of the central nervous system is mostly associated with this syndrome. Hydrocephalus, which is mostly associated with the type two malformation, can less frequently happen during type one (Loukas et al., 2011). The cause of hydrocephalus is an excessive accumulation of cerebrospinal fluid in the ventricles of the brain due to the block of its outflow. As a result, brain tissue is damaged due to limited space in the skull and a significant increase in intracranial pressure. The second complication of Chiari malformation, which is also caused by a disturbed cerebrospinal fluid passage is syringomyelia. During syringomyelia cavities are formed in the tissue of the spinal cord (Loukas et al., 2011). Very common are unusual sensations which patients start to experience. It can be paresthesias in the extremities, Lhermittes sign, loss of sensations in certain areas or restless leg syndrome (Koyanagi and Houkin, 2010). It should be considered that when the cavity is located laterally in the tissue of the spinal cord then at the early stages of the disease, happens a loss of temperature sensitivity and pain on one side of the body and during the time the loss of sensitivity progresses to the other half of the body. In children, Chiari malformation is also associated with the spinal curvature, particularly scoliosis or kyphosis. Furthermore, abnormal position of the cerebellar tonsils can cause their direct traumatization by the skull structures (the edge of the foramen magnum).
Speech is frequently affected by the Chiari malformation type one. There are a big amount of problems which can lead to the speech disorders in these patients. Syringomyelia, which often causes paresis and paralysis is associated with speech disorders. Because paresis from syringomyelia happens not only on limbs, muscles of the voice system also will be affected (Koyanagi and Houkin, 2010). Speech disorders may vary from dysphonia, caused by the vocal fold paresis, dysarthria, caused by cranial nerve nuclei lesions in the brain stem. Dysarthrias hindmost degree, when the patient loses the ability to speak due to paralysis of voice muscles is called anarthria. Speech problems may also arise from the damage of cerebellum, which will affect the impaired coordination of voice muscles and disability to speak quickly and legibly. Another common speech disorder, associated with the Chiari malformation type one is hoarseness. These motor disorders can be may be temporary, but often muscle function is not restored.
Language disorders are closely related to speech and cognition disorders. A severe stage of hydrocephalus can lead to the significant damage to the cortex and, consequently, loss of cognitive functioning - mental retardation. Patient with the certain level of mental retardation would find it difficult to chose the right words and clearly express their thoughts. In its turn, lesion of the language centers - so-called Broca and Wernicke areas would lead to corresponding types of aphasia (Mayoclinic.org, 2016). Aphasia is a neurogenic insufficiency of the person language. During the Broca aphasia, a person can understand what other people say, but when patient try to speak he can not form the right words and phrases and his language sounds like a set of sounds and syllables not linked semantically between themselves. Aphasia Wernicke has opposite signs and the nature of the language disorder. During this type, patient seemingly speaks freely and uses a variety of accurate words. On closer inspection it becomes absolutely clear that these patients have a problem with understanding the language. Their speech lacks key ideas and sounds like a and sounds like a set of random unconnected words.
Communication skills of the person with Chiari malformation frequently suffer as well. Increased intracranial pressure results in the papilledema, which can lead to significant vision impairment. In addition to the previous disorders that significantly impede communication, the communication is being affected by the disorders in sensory systems of the patient. For example, problems with the vision would include diplopia and blurred vision (Mayoclinic.org, 2016). These disorders would seriously interfere with the ability to interact with other people and get new information, given that most of the information we receive comes to us through vision organ. Disorders of the organ of hearing also are contributing to the deterioration of communication skills of Chiari malformation patients. While the cavity of the inner ear and subarachnoid space are connected, the increased intracranial pressure would affect hearing, causing tinnitus. Tinnitus is a high sound that resembles a bell to the patients (Loukas et al., 2011). It may vary from light noise which can be easily tolerated to the unbearable noise which makes it very difficult to communicate.
Swallowing problems that occur in patients with Chiari malformation arise from syringomyelia and are closely related to the speech disorders. Dysphagia results from the damage to the cranial nerve nuclei in the brainstem. It can vary from paresis to complete inability to swallow (Mayoclinic.org, 2016). Serious damage to the specified area can lead to the development of the bulbar palsy. Clinical signs of the bulbar palsy prove the close relationship between swallowing and speech disorders. It causes dysphagia, dysarthria and dysphonia simultaneously.
Cognitive functions suffer in the case of cerebellar damage, but their greatest the greatest manifestation happens in the case of the lesions in the cortex of the dominant hemisphere. This damage can be acquired through severe hydrocephaly and leads to the progressive mental retardation. Hydrocephalus, which causes the vast majority of cognitive disorders in Chiari malformation patients, is a problem which affects all almost the entire surface of the cerebral cortex. Therefore, its manifestations are diverse and include the impairment of all aspects of cognitive brain functions: memory, attention, social behavior, the process of learning, intellectual ability and in the most severe cases the self-care skills (Loukas et al., 2011).
References
Mayoclinic.org. (2016). Chiari malformation Symptoms - Mayo Clinic. [online] Available at: http://www.mayoclinic.org/diseases-conditions/chiari-malformation/basics/symptoms/con-20031115 [Accessed 21 Mar. 2016].
Furtado, S., Reddy, K. and Hegde, A. (2009). Posterior fossa morphometry in symptomatic pediatric and adult Chiari I malformation. Journal of Clinical Neuroscience, 16(11), pp.1449-1454.
Koyanagi, I. and Houkin, K. (2010). Pathogenesis of syringomyelia associated with Chiari type 1 malformation: review of evidences and proposal of a new hypothesis. Neurosurgical Review, 33(3), pp.271-285.
Loukas, M., Shayota, B., Oelhafen, K., Miller, J., Chern, J., Tubbs, R. and Oakes, W. (2011). Associated disorders of Chiari Type I malformations: a review. Neurosurgical FOCUS, 31(3), p.E3.
Schijman, E. (2004). History, anatomic forms, and pathogenesis of Chiari I malformations. Child's Nervous System, 20(5), pp.323-328.
