Arnold Chiari malformation: types, symptoms and main causes
Let's see what Arnold Chiari malformation is like, a disease that mainly affects the cerebellum.
Rare diseases (RD) are those with a low prevalence in the population. To be considered rare, a pathology must affect fewer than 5 out of every 10,000 inhabitants at any given place and time.
This data somewhat contradicts the reality observed on a practical level, as the World Health Organization (WHO) estimates that there are around 7,000 rare diseases affecting 7% of the global population. This is certainly not a negligible figure.
Today we bring you one of these rare pathologies which, at the beginning of the 20th century, was estimated to have a prevalence of 1 per 1,000 newborns. This figure has not remained valid over time because, unfortunately, new diagnostic techniques have shown that it is much more common than previously thought. Dive with us into the world of the patients with Arnold Chiari malformation.
What is Arnold Chiari malformation?
The Arnold Chiari malformation is a generally congenital disease, which consists of an anatomical alteration in the base of the skull of the newborn.. This pathology is characterized by the descent of part or almost all of the cerebellum through the foramen magnum (occipital foramen) into the cervical canal.
In other words, when a part of the skull is smaller than normal or deformed, the cerebellum is pushed into the foramen magnum and the spinal canal. This causes in the patient a series of characteristic symptoms, which are due to the following reasons:
- As part of the cerebellum moves into the cervical canal, it produces pressure on all the nerve endings, a fact that causes several symptoms.
- This cerebellar descent acts as a "plug", which causes an accumulation of cerebrospinal fluid and triggers other pathologies.
This rare, incapacitating and progressive disease affects 0.5% of the world's population, with 80% of the patients suffering from the disease.80% of patients are female. In addition to the seriousness of the most severe cases, several informative portals state that many children with this anomaly do not realize that they suffer from it, as they never show any symptoms.
Talking about the symptoms of the Arnold Chiari malformation is practically impossible without differentiating the different degrees in several blocks, since it is estimated that this group of central nervous system malformations includes more than 100 different clinical signs.. Therefore, here are the different types of the disease, classified according to the parts of the brain that extend into the spinal cavity. Let's go to it.
Patients with syringomyelia fall into this category. (a fluid-filled cyst within the spinal cord) with minimal or no data of tonsillar herniation (i.e. slippage of the cerebellum). The appearance of this fluid mass responds to a hydrodynamic alteration of the cerebrospinal fluid (CSF) at the level of the foramen magnum.
Type I is characterized by a dislocation of the cerebellar tonsils (the inner part of the cerebellum) through the foramen magnum (more than 5 millimeters). (more than 5 millimeters). This is the most common type and, fortunately, the patient may not have any obvious symptoms.
Although the overall incidence of this type of malformation is not well known, it is estimated that 50 to 70% of patients have associated syringomyelia and 10% of cases are also associated with hydrocephalus, ie, excessive accumulation of cerebrospinal fluid inside the skull.. It should be noted that this characteristic type is usually diagnosed from the second-third decade of life of the patient, as symptoms do not usually appear during childhood.
Among the most common signs and symptoms of Arnold Chiari malformation type I are the following:
- Loss of balance and dizziness.
- Neck pain.
- Vision problems and poor motor coordination.
- Swallowing difficulties and hoarseness.
- Change of habits when going to the bathroom.
However, it should be noted that 15 to 30% of patients with Chiari type I have no symptoms at any time. but, even so, symptomatic cases may be referred to medical specialists who address the pathology by surgery.
Moving up the scale of pathological severity, Chiari malformation type II usually shows more obvious symptoms and these develop during childhood. In this case a caudal herniation occurs through the foramen magnum of the cerebellar vermis, brainstem and fourth ventricle, i.e., a descent of the cerebellar tissue into the cerebellum.This is a more pronounced descent of the cerebellar tissue than in type I. This pathology can be a cause of death during infancy or early childhood and, unlike the two previous variants, requires surgery.
In addition to the symptoms listed above, patients with this type have syringomyelia and hydrocephalus in 90% of cases, but there is an accessory pathology: almost 15% of those affected may have spina bifida, i.e. a series of defects in the spine and spinal cord due to poor closure and development of the neural tube. Most infants with severe spina bifida die prematurely.
This is the rarest and most severe type of Arnold Chiari malformation.. In this case, the herniated cerebellum and brain stem enter the cervical spinal canal (often accompanied by the fourth ventricle of the brain) and compress the spinal cord. In addition to all the symptoms mentioned in type I and II, this variety presents associated severe neurological signs: severe mental and physical impairment and seizures, among others.
This is the most recently described type. Also known as cerebellar hypoplasia, it is characterized by an underdevelopment of the cerebellumthat is to say, this is located in its normal position, but some parts are missing. In this case there is no associated tissue hibernation.
Other pathologies associated with Arnold Chiari malformation.
As we have already seen in previous lines, syringomyelia and hydrocephalus are pathologies of joint presentation with this malformation, with spina bifida being of exceptional occurrence. Despite this, we have left out the following some physiological maladjustments associated with this specific clinical picture.. We show them to you briefly:
- Alterations in the volume of the posterior fossa: this small space in the skull is usually smaller in Chiari patients.
- Bone alterations: among many others, an example of this is the empty sella turcica, when the pituitary gland shrinks or becomes flattened.
- Alterations in ventricles, i.e. the four anatomical cavities through which the cerebrospinal fluid circulates. Hydrocephalus is an example.
- Meningeal abnormalities: several bands of dura mater (external meninx) compressing the foramen magnum are frequently found.
- Cerebral anomalies in all types except 0 and I.
As we can see, Arnold Chiari malformation presents with multiple signs, symptoms and accessory conditions. In general, depending on the severity of the clinical picture, cranial, spinal, ocular, otorhinolaryngologic, scoliosis, sleep problems, fatigue, axial skeletal pain and all the disorders we have mentioned above. Unfortunately, if there is one thing Chiari type II and III patients do not lack, it is aggressive and clear symptoms.
Rare diseases are those that affect less than 5 persons per 10,000 inhabitants and, despite being considered as such in several medical portals, Arnold Chiari malformation seems to affect 0.5% of the global population, that is, one in every 200 inhabitants, all this without counting the mild pathological pictures of type I that will never be diagnosed.
It is impressive to put these results into perspective because, if we take them into account, it is possible that more than one of the readers who have taken an interest in this space may have known someone with this malformation and not realized it. Of course, the more diagnostic tools advance, the more we realize that a rare disease may not be so rare.
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(Updated at Mar 28 / 2023)