Arnold-Chiari Malformation (Chiari Malformation Type 2)

Chiari malformations are a group of complex brain abnormalities.


Patients with type I CM do not show any symptoms. Adolescents and adults may develop symptoms of CM later in their life. Patients with CM often complain of neck pain or numbness. There are abnormal feelings in the extremities, muscle weakness and balance troubles. There are altered vision profiles, buzzing in the ears, vomiting, nausea, trouble in swallowing food, and hearing loss. Worsening of the conditions of this malformation leads to insomnia, sleep apnea, persistent headache and depression [3]. Patients may have difficulty in hand coordination and the fine motor skills are also affected.

Children and infants may show symptoms such as difficulty in swallowing and excessive drooling, weakness in arms, breathing problems and developmental delays. Parents are therefore advised to document the symptoms, and convey them to the pediatrician for early diagnosis.

Adult patients with type 1 CM, may initially present with benign paroxysmal vertigo and could be confused as a trivial benign positional vertigo [4]. Patients in the mid age may present with shortness of breath as an inaugural sign due to alveolar hypoventilation [5].


Though there are no specific symptoms associated with this malformation, it is often discovered only when complications arise.

Diagnostic tests

  • X-ray: Though X-ray of the head and neck cannot reveal the CM, it can help to identify the abnormalities associated with the bones related to CM.
  • Computed tomography (CT): This scan produces a 2-dimensional picture of the bone and the vascular irregularities, along with cyst formation or brain damage.
  • Magnetic resonance imaging (MRI): MRI will elucidate findings of tonsillar herniation of at least 5mm, overcrowding of structures by the foramen magnum and the underdevelopment of the posterior cranial fossa which clinches the definitive imaging diagnosis of type I CM [6]. A pre-surgical MRI evaluation of the cerebrospinal fluid flow in the foramen magnum may determine the degree of tonsillar herniation which correlates directly to the success rate of the operation [7].


If this disease does not show any symptoms and interfere with the daily activities, treatment is not necessary. Symptomatic treatment is quite common in the absence of the correct diagnosis, for example, if pain persists; analgesics are advised to manage the symptoms. However, if there are multiple symptoms that affect the patient on the day-to-day basis, surgery is the only treatment modality that can cease the progression of the disease. The goal of surgery in Chiari malformation is two-fold:

  1. Relief of the pressure on the brain and the spinal cord.
  2. Restoring the fluid circulation in and around the area.

Some of the common surgical procedures performed in patients with CM are as follows:

  • Posterior fossa decompression surgery: In this surgery, there is a removal of the portion of the bottom of the skull or the spinal cord to correct the altered bony structures. In the procedure, the dura is also opened and widened, creating an additional space for the fluid to circulate. Foramen magnum decompression procedures resolves primary signs and help resolve complications like syringomyelia [8].
  • Electrocautery: High frequency electrical current helps to shrink the lower part of the cerebellum making the space needed.
  • Spinal laminectomy: In this procedure, the part of the bony roof of the spinal canal is removed, thus increasing the size and reducing the pressure on the spinal cord.

Surgery of the malformation has shown to reduce the symptoms significantly, prolonging the periods of remission.


Type I CM is generally asymptomatic. In complicated cases, surgery can help to reduce the symptoms associated with the malformation.


There are cases documented where CM becomes progressive, leading to serious complications. The complications associated with the disorder are as follows:

  • Hydrocephalus: This is a condition in which there is an excess accumulation of cerebrospinal fluid in the brain, thus requiring the placement of the shunt to drain this excess fluid.
  • Spina bifida: This is the condition in which the spinal cord or its covering is not fully developed, and forms a manifestation of ACM. Serious complications such as paralysis is common in such patients.
  • Syringomyelia: There can be an appearance of the cyst or cavity which is formed within the spinal cord. This is referred to as syringomyelia. The untreated syringomyelia may complicate with neuropathic arthropathy which are more marked in the elbows [2].
  • Tethered cord syndrome: Sometimes the spinal cord gets stretched causing severe nerve and muscle damage to the lower part of the body.


The causes of Chiari malformations are categorized into primary and secondary. Primary CM can occur with the structural defects in the brain or the spinal cord during the fetal development either due to lack of the proper nutrient in the maternal diet (during development) or genetic mutations. Hence, this is called primary or congenital CM. Primary CM is more common than the secondary CM. When the CM occurs later in life, it is called secondary or acquired CM. This can happen if there is an excessive drainage of the spinal fluid from the lumbar or thoracic areas of the spine which can occur either because of injury or infection.

Depending on the severity of the CM and the parts of the brain affected, Chiari malformation can be divided into type I, type II, type III and type IV.

  • In type I CM, there is an extension of the lower parts of cerebellum into the foramen magnum and may not cause many symptoms. It is the common type, often noticed in adolescence.
  • Type II is also referred to as classic CM. This involves the extension of both the cerebellar and brain tissues. Arnold Chiari malformation is often used to specifically refer to type II malformation.
  • The most serious type of CM is type III. In this, the brainstem and the cerebellum protrude through the foramen magnum into the spinal cord. This type of ACM causes the most severe neurological defects.
  • In type IV CM, there is an incomplete or underdeveloped cerebellum.
  • In recent times, type 0 CM is also included in the classification. In Type 0, though there is no protrusion of the cerebellum, the patient may experience symptoms that mimic that of CM.

Primary type I CM is also attributed to the linkages to chromosomes 9 and 15. It is suggested that the disorder occurs in the para-axial mesoderm, resulting in the formation of the smaller posterior fossa. There are other theories regarding the cause of Arnold Chiari Malformation, one of the interesting one is called “CSF loss theory”. According to this hypothesis, there is an escape of the fluid in the myelomeningocele which results in inadequate stimuli of the mesenchymal condensation at the base of the skull.


Earlier it was believed that CM occurred one in every 1,000 births. With the development of the diagnostic imaging in the past few decades, the occurrence is found to be more common. Today CM may reach up to 5 cases per 1000 births with female predominance over male subjects [1]. Since, there are cases where the child born with ACM does not show symptoms until they reach adolescence, the exact epidemiological profile of the disease is still not known. The disorder is more common among women than men. Type II malformations are more prevalent among the different types of CM.

Sex distribution
Age distribution


The pathophysiological complications that lead to the consequences of this malformation can be due to the following:

  1. Compression of the medulla, upper spinal cord and/or cerebellum. The complications associated with the medulla and the cord can result into myelopathy and nuclear dysfunction. Ataxia and nystagmus or loss of equilibrium is associated with the compression of the cerebellum.
  2. Disruption of the flow of the CSF through the foramen magnum causes the symptoms of pain which are associated with CM.


There are no preventive measures to combat Arnold Chiari malformation; genetic counseling can prove beneficial to the parents of the child to determine the risk in future children.


Chiari malformations (CM) are a group of congenital abnormalities that affect the hindbrain. In the CMs, the part of the cerebellum is located below the foramen magnum in the brain, and may develop when the bony space is smaller than the normal, causing the brainstem to be pushed downward to the foramen magnum. The pressure that ensues due to this structural deformity on the cerebellum and brainstem affects the functions, blocking the flow of cerebrospinal fluid (CSF).

Patient Information

Patients with Arnold Chiari malformation (ACM) generally do not show any symptoms, therefor the condition is often diagnosed during the course of diagnosis for another disorder. However, there may be symptoms such as headache, dizziness, vomiting and nausea. Medical and surgical options are available for the treatment of this disorder.


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