What are Chiari Malformations?

Causes of CM
CM-0 (Type 0)
CM-I (Type 1)
CM-II (Type 2)
CM-III (Type 3)
CM-IV (Type 4)
Epidemiology of CM
Diagnosis and Treatment of CM

Chiari malformations are a heterogeneous group of disorders comprising abnormalities associated with the hindbrain. The most common types are Chiari 1 malformation (CM-I) and Chiari 2 malformation (CM-II). Hydrocephalus, spina bifida, scoliosis, hydromyelia, syringomyelia, and tethered cord syndrome are all related to these deformities.

Chiari malformations are uncommon, but their symptoms can affect adults' and children's quality of life, disrupting jobs or education and social exclusion. Chiari malformations come in various shapes and sizes, but they all have the same feature: the hindbrain projecting through the foramen magnum and into the spinal canal.

Chiari malformations

Image Credit: Mamat Suryadi/Shutterstock.com

Causes of CM

A variety of unidentified factors causes Chiari malformations. These deformities and the anomalies of the central nervous system that they cause are very complicated. Chiari malformations are thought to be caused by an unidentified developmental failure of a developing fetus's brainstem and upper spinal cord (cervical region). Some researchers believe that the development of a Chiari malformation is aided by an abnormally tiny posterior fossa, which is the place where the cerebellum ordinarily rests.

CM-0 (Type 0)

Syringohydromyelia that responds to craniocervical decompression with no or little (3 mm) tonsillar herniation is known as Chiari malformation type 0 (CM-0). Disrupted CSF flow at the craniocervical junction causes symptoms in CM-0. This has led to terms like "borderline Chiari" and "Chiari-like pathophysiology," as well as descriptions like "tight cisterna magna" from other authors.

Iskandar et al., who reported five comparable cases in which the symptoms and size of the syrinx improved after posterior cerebral fossa decompression, coined the designation Chiari malformation type 0 in 1998. Since then, the number of CM-0 case reports has increased, while they are still few. Patients with CM-0 have a clinical profile that is similar to CM-I.

CM-I (Type 1)

CM-I is a congenital disorder that usually manifests in childhood or early adulthood. This is the mildest of the three types. The format of the presentation is varied. The most common presenting symptom is a headache. A sub-occipital headache or neck discomfort produced or aggravated by Valsalva-like moves is how it's usually defined (such as coughing).

Ocular or otoneurological symptoms are reported by more than 75% of individuals. Neck, shoulder, and back pain, motor and sensory abnormalities in the limbs, and/or trouble with balance and coordination are all possible presenting symptoms. Although the routes of inheritance are unknown, a familial link has been documented in 3-12 % of CM-I cases.

CM-II (Type 2)

Although CM-II is present at birth, it is increasingly being detected prenatally through anomaly screening. Symptoms affect one out of every five children with CM2. This is the most common variation.

The 'classic' or 'Arnold–Chiari' deformity is another name for it. In more than 70% of instances, hydrocephalus is present. Spina bifida and other brain, spinal, and meningeal disorders are linked. A neuroectodermal disorder causes it. Girls are significantly more likely than boys to have CM-II.

CM-III (Type 3)

CM-III is an uncommon type of malformation. Because of an accompanying Dandy-Walker deformity or aqueductal stenosis, hydrocephalus is present in 50% of cases and is of the obstructive type. In an occipital, cervical, or occipital–cervical meningocele, the medulla is displaced caudally, and a portion of the cerebellum is herniated. A portion of the hindbrain may also be herniated. It is caused by a neuroectodermal abnormality.

CM-IV (Type 4)

This is the least common but most severe form of CM, with an incomplete or undeveloped cerebellum (cerebellar hypoplasia or aplasia), pons abnormalities, and a brainstem 'pigeon breast' malformation. Although hydrocephalus is uncommon, these structural changes produce dilation of the fourth ventricle, cisterna magna, and basal cisterns. It is a type of neuroectodermal abnormality.

Epidemiology of CM

The prevalence of CM is estimated to be between 0.1 and 0.5 %. Most clinical cohort studies demonstrate an equal or slight female predominance in both sexes. There is no recognized risk factor other than family history and no ethnic or geographical distribution.

Diagnosis and Treatment of CM

Diagnosis is based on a thorough clinical examination and evaluation. Clinical findings differ depending on the patient's age at the presentation time. The diagnosis of CM1 is ultimately anatomical, and cross-sectional neuroimaging confirms it. Prenatal or postnatal imaging is used to identify CM2. For spina bifida, ultrasonography is 97% sensitive and 100% specific. The diagnosis of CM0 can only be fully validated after the patient's clinical course improves following posterior cerebral fossa decompression.

The therapy of a Chiari malformation focuses on the specific symptoms that each person experiences. Depending on the severity of the symptoms and the patient's wishes, CM1 is treated conservatively or surgically. Patients with no or minor symptoms can be conservatively handled with regular follow-up. In counseling individuals with Chiari malformations and their families, it's vital to provide enough evidence-based information.

The treatment of patients with CM2 (from childhood to adulthood) goes hand in hand with the treatment of myelomeningocele. Surgical closure of the myelomeningocele is usually done at a hospital with a pediatric neurosurgery service between 24-72 hours of birth.

The therapy of choice for patients with CM0 is posterior cerebral fossa decompression, which restores normal CSF flow. To achieve a positive response to treatment, patients must be carefully selected and diagnosed with CM0 only after other causes of syringohydromyelia have been ruled out.

To choose the best treatment, it's critical to distinguish and recognize these diverse malformations. When all potential hazards and problems are considered, craniocervical decompression is a safe and successful treatment. It can slow the progression of clinical and radiological deterioration in children with Chiari malformation symptoms or syringomyelia. The outcome can be reasonably successful if the indication for surgical treatment is correct.


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Further Reading

Last Updated: Feb 24, 2023

Emily Henderson

Written by

Emily Henderson

During her time at AZoNetwork, Emily has interviewed over 300 leading experts in all areas of science and healthcare including the World Health Organization and the United Nations. She loves being at the forefront of exciting new research and sharing science stories with thought leaders all over the world.


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