Chiari malformation




Chiari malformation, formerly known as Arnold-Chiari syndrome, is a malformative disease of the nervous system, present at birth (congenital), which affects the cerebellum, the brainstem and the back of the skull (posterior fossa). It is characterized by the "sliding" or herniation of parts of the cerebellum (as well as parts of the brain stem) through the hole between the skull and the spinal canal (foramen magnum). Other malformations of the brain and spinal cord (syringomyelia) may also be associated with the disease.

There are four main types of Chiari malformation in relation to the severity and complexity of the disorders it causes (clinical picture):

  • type 1, called Chiari I, is the most common and consists in the sliding of two small lobes present in the lower face of the cerebellum, the cerebellar tonsils, inside the spinal canal through the foramen magnum. The Chiari I malformation must be distinguished from the "primitive herniation of the cerebellar tonsils" , defined today as Chiari deformity
  • in some cases, Chiari I malformation may be associated with spinal cord malformations such as syringoidromyelia.
  • type II, III and IV, these are more complex Chiari malformations involving the brain, cerebellum, spinal cord, base of the skull and spine

Severity of Chiari I malformation

The severity of the disease can vary from person to person but, in general:

  • it is not considered life-threatening
  • some people may suffer from headaches (headache), movement problems while others do not complain of any ailments
  • syringomyelia may be present (cystic cavities in the spinal cord) which, if not treated properly, can cause various complications
  • surgical therapy, to be evaluated with the specialist, can improve some aspects related to the malformation, although other ailments may persist

In Italy, Chiari malformation is entered as Arnold-Chiari syndromein the "list of rare diseases exempt from the cost of the ticket (Annex 7 of the DPCM 12 January 2017) with the code RN0010. It is possible to have information on the disease, to know the procedure for the exemption, the clinical diagnosis and treatment centers of the Network national rare diseases and patient associations by contacting the Rare Diseases Toll-Free Telephone (TVMR) 800.89.69.49 from Monday to Friday from 9.00 to 13.00.



Chiari malformation often does not cause disorders (symptoms) and is discovered by chance during the execution of a magnetic resonance imaging (MRI) of the brain performed for other reasons. When present, disorders generally include:

  • headache which usually affects the back of the head and can be triggered or aggravated by coughing, straining, sneezing, or bending over
  • neck pain
  • dizziness and balance problems
  • muscle weakness
  • numbness or tingling in the arms or legs
  • blurred vision, double vision and sensitivity to light
  • swallowing problems
  • hearing reduction and tinnitus (tinnitus)
  • sleep disorders (insomnia)
  • mood changes

In the presence of syringomyelia, difficulty in moving the hands, disturbances in walking, pain, and problems controlling bladder or bowel may occur.



The cause of Chiari I malformation to date is not fully known. The malformation is present at birth but is usually ascertained (diagnosed) in the following years, in relation to the appearance of the disorders (clinical manifestations) caused by the disease or on the occasion of neuroradiological investigations carried out for other reasons.

It is believed that the Chiari I malformation is due to a defect in the embryonic development of the bones of the posterior cranial fossa, the one that will accommodate the cerebellum, which remains smaller than normal.

Chiari malformations can sometimes be family-related, suggesting a genetic component underlying the defect. This is also supported by the finding of this malformation in several pairs of monozygotic twins.

It is therefore possible that some babies born with the malformation may have a defective gene that influenced the development of the skull and some nerve structures. However, the risk of inheriting a Chiari malformation is very low.

Chiari I malformation can also be secondary to other diseases such as, for example: anchored spinal cord, hydrocephalus and some brain tumors.



The assessment (diagnosis) of Chiari I malformation, in patients with or without disorders (symptoms), is carried out using nuclear magnetic resonance (MRI). The investigation can also be used to evaluate the volume of the posterior cranial fossa and the dynamics of the cerebrospinal fluid.

To exclude the presence of malformations in the spinal cord it is useful, both in the research phase of the disease (diagnosis), and in subsequent checks (follow up), to check this part of the nervous system with the MRI.

Radiographic examination and computed axial tomography (CT) are indicated to study bony abnormalities of the skull.



The treatment of Chiari I malformation depends on the severity of the disorders (symptoms) present. In the absence of symptoms, no treatment is needed.

Pain relievers can help relieve any headaches and neck pains.

For more complex disorders such as, for example, those caused by an increase in the pressure of the CSF (fluid that is found around the brain and spinal cord), it is necessary to evaluate surgical therapy.


Most of the time, Chiari malformation is treated surgically with decompression surgery which, in addition to reducing pressure on the brain, allows the cerebro-spinal fluid (present in and around the brain and spinal cord) to flow normally.

Other surgical procedures that may be needed in the treatment of Chiari malformation include the endoscopic ventriculostomy (ETV), lo ventriculo-peritoneal shunt, the section of the filum terminalis of the spinal cord and the vertebral fixation. The latter must be performed if a Chiari I malformation is associated with a joint hypermobility syndrome, as the Ehlers-Danlos syndrome, which requires surgery to stabilize the spine.

Post-operative complications may include neurological disorders, meningitis, infections, CSF loss, and pseudomeningocele.



Perrini P, Anania Y, Cagnazzo F, Benedetto N, Morganti R, Di Carlo DT. Radiological outcome after surgical treatment of syringomyelia-Chiari I complex in adults: a systematic review and meta-analysis [Summary]. Neurosurgical Review. 2020 Jan 17

Langston TH, Batzdorf U. Chiari malformation and syringomyelia. Journal of Neurosurgery: Spine 31:619–628, 2019

Zagzoog N, Reddy KK. Use of Minimally Invasive Tubular Retractors for Foramen Magnum Decompression of Chiari Malformation: A Technical Note and Case Series [Summary]. World Neurosurgery. 128:248-253, 2019

Piper RJ, Pike M, Harrington R, Magdum SA. Chiari malformations: principles of diagnosis and management [Summary]. BMJ. 365: l1159, 2019

NHS Choices. Chiari malformation (English)

Poretti A, Ashmawy R, Garzon-Muvdi T, Jallo GI, Huisman TA, Raybaud C. Chiari Type 1 Deformity in Children: Pathogenetic, Clinical, Neuroimaging, and Management Aspects [Summary]. Neuropediatrics. 47:293, 2016 

Wilkinson DA, Johnson K, Garton HJ, Muraszko KM, Maher CO. Trends in surgical treatment of Chiari malformation Type I in the United States. Journal of Neurosurgery: Pediatrics. 19:208, 2017

Arnautovic A, Splavski B, Boop FA, Arnautovic KI. Pediatric and adult Chiari malformation Type I surgical series 1965-2013: a review of demographics, operative treatment, and outcomes. Journal of Neurosurgery: Pediatrics. 15:161, 2015

In-depth link

In-depth link

Italian Association of Syringomyelia and Arnold Chiari (AISMAC)

Italian Chiari Child Malformation Association (AIMA Child)

OMIM - Online Mendelian Inheritance in Man. Chiari malformation type I (English)

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