Chiari malformation

Findings are due to brainstem and lower cranial nerve dysfunction. Onset of symptoms are less likely to be present during adulthood in most patients. Younger children generally have a substantially different presentation of clinical symptoms from older children. Younger children are more likely to have a more rapid neurological degeneration with profound brainstem dysfunction over several days.{{Citation |last1=Kuhn |first1=James |title=Chiari Malformation Type 2 |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK557498/ |access-date=2025-03-06 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32491430 |last2=Weisbrod |first2=Luke J. |last3=Emmady |first3=Prabhu D.}}

Headache is the most common symptom in those with Chiari malformation type 1 (in which only the cerebellar tonsils descend below the foramen magnum). This headache is usually occipital or sub-occipital in location (but may also present in other cranial areas), is usually dull or throbbing in character and is characteristically associated with Valsalva maneuvers (such as bearing down, coughing, sneezing, bending over or forcefully exhaling against a closed airway).{{cite journal |last1=Friedlander |first1=Robert M. |title=Congenital and Acquired Chiari Syndrome |journal=New England Journal of Medicine |date=20 June 2024 |volume=390 |issue=23 |pages=2191–2198 |doi=10.1056/NEJMra2308055|pmid=38899696 }}Considering a headache is one of the most common symptoms, it is important to note that a tension headache is also a common repetative sign before diagnosis.{{Cite journal |last1=Thunstedt |first1=Dennis C. |last2=Schmutzer |first2=Michael |last3=Fabritius |first3=Matthias P. |last4=Thorsteinsdottir |first4=Jun |last5=Kunz |first5=Mathias |last6=Ruscheweyh |first6=Ruth |last7=Straube |first7=Andreas |date=2022 |title=Headache characteristics and postoperative course in Chiari I malformation |journal=Cephalalgia: An International Journal of Headache |volume=42 |issue=9 |pages=879–887 |doi=10.1177/03331024221079296 |issn=1468-2982 |pmc=9315190 |pmid=35236163}}

Symptoms that may be due to Chiari malformations include:

• Neurogenic dysphagia: Difficulty swallowing.
• Cyanosis: Bluish discoloration of skin while feeding.
• Weak crying
• Facial weakness
• Aspiration
• Headaches aggravated by Valsalva maneuvers{{cite journal |vauthors=Riveira C, Pascual J |title=Is Chiari type I malformation a reason for chronic daily headache |journal=Current Pain and Headache Reports |volume=11 |issue=1 |pages=53–5 |date=February 2007 |pmid=17214922 |doi=10.1007/s11916-007-0022-x |s2cid=41199446}}
• Tinnitus (ringing in the ears)
• Lhermitte's sign (electrical sensation that runs down the back and into the limbs)
• Vertigo (dizziness)
• Nausea
• Schmahmann's syndrome
• Nystagmus (irregular eye movements; typically, so-called "downbeat nystagmus")
• Facial pain
• Muscle weakness
• Impaired gag reflex
• Dysphagia (difficulty swallowing){{cite web |title=Chiari malformation - symptoms |publisher=University of Washington - Department of Neurological Surgery - Chiari Malformation Clinic |url=http://depts.washington.edu/neurosur/chiari/chiari_symptoms.htm |access-date=November 4, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20101121000602/http://depts.washington.edu/neurosur/chiari/chiari_symptoms.htm |archive-date=November 21, 2010}}
• Restless leg syndrome
• Sleep apnea
• Sleep disorders{{cite web |title=Mystery of Sleepless Boy Solved |website=ABC News |url=https://abcnews.go.com/GMA/OnCall/mystery-sleepless-boy-solved/story?id=6711810}}{{cite web |title=Medical Mystery: The Boy Who Couldn't Sleep |website=ABC News |url=https://abcnews.go.com/GMA/Sleep/medical-mystery-boy-sleep/story?id=4828035}}
• Impaired coordination
• Severe cases may develop all the symptoms and signs of a bulbar palsy
• Paralysis due to pressure at the cervico-medullary junction may progress in a so-called "clockwise" fashion, affecting the right arm, then the right leg, then the left leg, and finally the left arm; or the opposite way around.{{citation needed|date=June 2015}}{{cite web |title=Chiari malformation |publisher=Mayo Clinic |url=https://www.mayoclinic.org/diseases-conditions/chiari-malformation/symptoms-causes/syc-20354010 |access-date=10 May 2020}}
• Papilledema on fundoscopic exam due to increased intracranial pressure
• Pupillary dilation
• Dysautonomia: tachycardia (rapid heart), syncope (fainting), polydipsia (extreme thirst), chronic fatigue{{cite web |title=Dysautonomia News – Winter/Spring 2006 |publisher=Dinet.org |url=http://www.dinet.org/Winter_Spring2006/ws06news4.htm |access-date=November 4, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20111129074959/http://dinet.org/Winter_Spring2006/ws06news4.htm |archive-date=November 29, 2011}}
• Apnea: Sudden pause of breathing, usually during sleep.
• Opisthotonos: Spasm of the head which causes head to arch backwards. More common in infants than adults.
• Stridor

The blockage of cerebrospinal fluid (CSF) flow may also cause a syrinx to form, eventually leading to syringomyelia. Central cord symptoms such as hand weakness, dissociated sensory loss, and, in severe cases, paralysis may occur.{{EMedicine|article|1483583|Chiari Malformation}}

{{Main|Syringomyelia}}

Syringomyelia is most often chronic progressive degenerative disorder characterized by a fluid-filled cyst located in the spinal cord. However, there can be also cases where the syrinx in terms of size and extent of symptoms actually stays stable throughout a lifetime. Syringomyelia symptoms include pain, weakness, numbness, and stiffness in the back, shoulders, arms or legs. Other symptoms include headaches, the inability to feel changes in the temperature, sweating, sexual dysfunction, and loss of bowel and bladder control. It is usually seen in the cervical region but can extend into the medulla oblongata and pons or it can reach downward into the thoracic or lumbar segments. Syringomyelia is often associated with type I Chiari malformation and is commonly seen between the C-4 and C-6 levels. The exact development of syringomyelia is unknown but many theories suggest that the herniated tonsils in type I Chiari malformations cause a "plug" to form, which does not allow an outlet of CSF from the brain to the spinal canal. Syringomyelia is present in 25% of patients with type I Chiari malformations.{{cite journal |author1=Adnan BURINA |author2=Dževdet SMAJLOVIĆ |author3=Osman SINANOVIĆ |author4=Mirjana VIDOVIĆ |author5=Omer Ć. IBRAHIMAGIĆ |title=ARNOLD–CHIARI MALFORMATION AND SYRINGOMYELIA |journal=Acta Med Sal |volume=38 |pages=44–46 |year=2009 |doi=10.5457/ams.v38i1.31 |doi-access=free |url=https://saliniana.com.ba/index.php/ams/article/view/ams.31.09/39}}

File:Foramen magnum - inferior view - animation.gif

The most common pathophysiological mechanism by which Chiari type I malformations occurs is due to a congenitally small posterior fossa. Other pathophysiological mechanisms involve increased intracranial pressure above the foramen magnum which causes a downward pressure against the cerebellum, thus causing the cerebellar tonsils to displace below the foramen magnum. Such causes include hydrocephalus (an accumulation of cerebrospinal fluid [CSF] around the brain), space occupying lesions in the brain such as tumors, subdural hematomas or other subdural fluid collections, arachnoid cysts, craniosynostosis (early closure of the cranial sutures)(especially of the lambdoid suture), hyperostosis (an excessive growth of bone) (such as craniometaphyseal dysplasia, osteopetrosis).{{cite journal |vauthors=Loukas M, Shayota BJ, Oelhafen K, Miller JH, Chern JJ, Tubbs RS, Oakes WJ |title=Associated disorders of Chiari Type I malformations: a review |journal=Neurosurgical Focus |volume=31 |issue=3 |pages=E3 |date=September 2011 |pmid=21882908 |doi=10.3171/2011.6.FOCUS11112 |doi-access=free |s2cid=45262171}} Another pathophysiological mechanism by which Chiari malformations form is by negative pressure or a pulling force from below the foramen magnum which pulls against the brain, causing the cerebellar tonsils to herniate past the foramen magnum. Causes of this negative or pulling pressure include a tethered cord or an excessively tense Filum terminale, a cerebrospinal fluid leak creating a negative pressure around the spinal cord as the fluid surrounding the cord leaks out, or a CSF-venous fistula, in which the CSF leaks into a nearby vein.{{cite web |title=Malformación de Arnold Chiari |language=es |website=Institut Chiari de Barcelona |url=https://institutchiaribcn.com/arnold-chiari/}}

Traumatic brain injury may cause delayed acquired Chiari malformation, but the pathophysiology of this is unknown.{{cite journal |vauthors=Moscote-Salazar LR, Zabaleta-Churio N, Alcala-Cerra G, M Rubiano A, Calderon-Miranda WG, Alvis-Miranda HR, Agrawal A |title=Symptomatic Chiari Malformation with Syringomyelia after Severe Traumatic Brain Injury: Case Report |journal=Bulletin of Emergency and Trauma |volume=4 |issue=1 |pages=58–61 |date=January 2016 |pmid=27162930 |pmc=4779473}} This is due to the fact that the condition can go asymptomatic for years and a diagnosis is often led through testing for a variety of symptoms.{{Cite web |title=Lueder, Larkin & Hunter {{!}} Alleged Traumatic Brain Injuries: Causation Issues with Chiari Malformations |url=https://www.luederlaw.com/alleged-traumatic-brain-injuries-causation-issues-with-chiari-malformations/#:~:text=However,%20in%20the%20Fischbein%20study,reported%20cases%20of%20Chiari%20malformations. |access-date=2025-05-05 |website=www.luederlaw.com |language=en-US}} Additionally, ectopia may be present but asymptomatic until a whiplash injury causes it to become symptomatic.{{cite journal |vauthors=Freeman MD, Rosa S, Harshfield D, Smith F, Bennett R, Centeno CJ, Kornel E, Nystrom A, Heffez D, Kohles SS |title=A case-control study of cerebellar tonsillar ectopia (Chiari) and head/neck trauma (whiplash) |journal=Brain Injury |volume=24 |issue=7–8 |pages=988–94 |year=2010 |pmid=20545453 |doi=10.3109/02699052.2010.490512 |s2cid=9553904}} Other conditions linked to Chiari malformations include X-linked vitamin D-resistant rickets, and neurofibromatosis type I.{{Cite journal |last1=Kuether |first1=T. A. |last2=Piatt |first2=J. H. |date=1998 |title=Chiari malformation associated with vitamin D-resistant rickets: case report |url=https://pubmed.ncbi.nlm.nih.gov/9588565 |journal=Neurosurgery |volume=42 |issue=5 |pages=1168–1171 |doi=10.1097/00006123-199805000-00134 |issn=0148-396X |pmid=9588565}}

Diagnosis is made through a combination of patient history, neurological examination, and medical imaging.{{cite journal |last1=Ciaramitaro |first1=Palma |last2=Massimi |first2=Luca |last3=Bertuccio |first3=Alessandro |last4=Solari |first4=Alessandra |last5=Farinotti |first5=Mariangela |last6=Peretta |first6=Paola |last7=Saletti |first7=Veronica |last8=Chiapparini |first8=Luisa |last9=Barbanera |first9=Andrea |last10=Garbossa |first10=Diego |last11=Valentini |first11=Laura |date=2021-06-15 |title=Diagnosis and treatment of Chiari malformation and syringomyelia in adults: international consensus document |journal=Neurological Sciences |volume=43 |issue=2 |pages=1327–1342 |issn=1590-3478 |pmid=34129128 |doi=10.1007/s10072-021-05347-3 |s2cid=235438643 |url=https://pubmed.ncbi.nlm.nih.gov/34129128}}{{cite web |title=Chiari malformations |website=Institute for Neurology and Neurosurgery |publisher=Northwell Health |language=en |url=https://www.northwell.edu/neurosciences/conditions/chiari-malformations |access-date=2023-03-28}} Magnetic resonance imaging (MRI) is considered the preferred imaging modality for Chiari malformation.{{cite journal |last1=McClugage |first1=Samuel G. |last2=Oakes |first2=W. Jerry |date=September 2019 |title=The Chiari I malformation: JNSPG 75th Anniversary Invited Review Article |journal=Journal of Neurosurgery: Pediatrics |volume=24 |issue=3 |pages=217–226 |issn=1933-0707 |pmid=31473667 |doi=10.3171/2019.5.PEDS18382 |doi-access=free |url=https://thejns.org/view/journals/j-neurosurg-pediatr/24/3/article-p217.xml|url-access=subscription }} The MRI visualizes neural tissue such as the cerebellar tonsils and spinal cord as well as bone and other soft tissues. CT and CT myelography are other options and were used prior to the advent of MRI, unfortunately the resolution of CT based modalities do not characterize syringomyelia and other neural abnormalities as well.{{cite web |title=Chiari Malformations |website=The Lecturio Medical Concept Library |url=https://www.lecturio.com/concepts/chiari-malformations/ |access-date=5 July 2021}}

By convention, the cerebellar tonsil position is measured relative to the basion-opisthion line, using sagittal T1 MRI images or sagittal CT images.{{cite journal |vauthors=Barkovich AJ, Wippold FJ, Sherman JL, Citrin CM |title=Significance of cerebellar tonsillar position on MR |journal=AJNR. American Journal of Neuroradiology |volume=7 |issue=5 |pages=795–9 |year=1986 |pmid=3096099 |pmc=8331977}} The selected cutoff distance for abnormal tonsil position is somewhat arbitrary, as not every person will be symptomatic at a certain amount of tonsil displacement, and the probability of symptoms and syrinx increases with greater displacement; however, greater than 5 mm is the most frequently cited cutoff number, though some consider 3–5 mm to be "borderline"; pathological signs and syrinx may occur beyond that distance.{{cite journal |vauthors=Aboulezz AO, Sartor K, Geyer CA, Gado MH |title=Position of cerebellar tonsils in the normal population and in patients with Chiari malformation: a quantitative approach with MR imaging |journal=Journal of Computer Assisted Tomography |volume=9 |issue=6 |pages=1033–6 |year=1985 |pmid=4056132 |doi=10.1097/00004728-198511000-00005 |s2cid=37901812}}{{cite journal |vauthors=Chern JJ, Gordon AJ, Mortazavi MM, Tubbs RS, Oakes WJ |title=Pediatric Chiari malformation Type 0: a 12-year institutional experience |journal=Journal of Neurosurgery. Pediatrics |volume=8 |issue=1 |pages=1–5 |date=July 2011 |pmid=21721881 |doi=10.3171/2011.4.peds10528 |s2cid=2220301}} One study showed little difference in cerebellar tonsil position between standard recumbent MRI and upright MRI for patients without a history of whiplash injury. Neuroradiological investigation is used to first rule out any intracranial condition that could be responsible for tonsillar herniation. Neuroradiological diagnostics evaluate the severity of crowding of the neural structures within the posterior cranial fossa and their pressure against the foramen magnum. Chiari 1.5 is a term used when both brainstem and tonsillar herniation through the foramen magnum are present.{{cite journal |vauthors=Tubbs RS, Iskandar BJ, Bartolucci AA, Oakes WJ |title=A critical analysis of the Chiari 1.5 malformation |journal=Journal of Neurosurgery |volume=101 |issue=2 Suppl |pages=179–83 |date=November 2004 |pmid=15835105 |doi=10.3171/ped.2004.101.2.0179}}

The diagnosis of a Chiari II malformation can be made prenatally, through ultrasound.{{cite journal |vauthors=Cui LG, Jiang L, Zhang HB, Liu B, Wang JR, Jia JW, Chen W |title=Monitoring of cerebrospinal fluid flow by intraoperative ultrasound in patients with Chiari I malformation |journal=Clinical Neurology and Neurosurgery |volume=113 |issue=3 |pages=173–6 |date=April 2011 |pmid=21075511 |doi=10.1016/j.clineuro.2010.10.011 |s2cid=22878869}}

In the late 19th century, Austrian pathologist Hans Chiari described seemingly related anomalies of the hindbrain, the so-called Chiari malformations I, II and III. Later, other investigators added a fourth (Chiari IV) malformation. The scale of severity is rated I – IV, with IV being the most severe. Types III and IV are very rare.{{cite web |title=Arnold Chiari Malformation |url=http://neurosurgery.ucla.edu/body.cfm?id=109 |access-date=July 17, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20100707054427/http://neurosurgery.ucla.edu/body.cfm?id=109 |archive-date=July 7, 2010}} Since Dr. Chiari's original descriptions Chiari 0, 1.5, 3.5, and 5 have been described in the medical literature.{{cite journal |vauthors=Iskandar BJ, Hedlund GL, Grabb PA, Oakes WJ |title=The resolution of syringohydromyelia without hindbrain herniation after posterior fossa decompression |journal=Journal of Neurosurgery |volume=89 |issue=2 |pages=212–6 |date=August 1998 |pmid=9688115 |doi=10.3171/jns.1998.89.2.0212}}{{cite journal |vauthors=Fisahn C, Shoja MM, Turgut M, Oskouian RJ, Oakes WJ, Tubbs RS |title=The Chiari 3.5 malformation: a review of the only reported case |journal=Child's Nervous System |volume=32 |issue=12 |pages=2317–2319 |date=December 2016 |pmid=27679454 |doi=10.1007/s00381-016-3255-3 |s2cid=11329088}}{{cite journal |vauthors=Tubbs RS, Muhleman M, Loukas M, Oakes WJ |title=A new form of herniation: the Chiari V malformation |journal=Child's Nervous System |volume=28 |issue=2 |pages=305–7 |date=February 2012 |pmid=22038152 |doi=10.1007/s00381-011-1616-5 |s2cid=3255189}}

File:Neck MRI 130850-dichromatic t1-t2-t2.png

Other conditions sometimes causally associated with Chiari malformation include hydrocephalus,{{cite web |title=Neuropathology For Medical Students |url=http://www.pathology.vcu.edu/WirSelfInst/neuro_medStudents/devdis.html |url-status=dead |archive-url=https://web.archive.org/web/20080708203920/http://www.pathology.vcu.edu/WirSelfInst/neuro_medStudents/devdis.html |archive-date=July 8, 2008}} syringomyelia, spinal curvature, tethered spinal cord syndrome, and connective tissue disorders{{cite journal |vauthors=Milhorat TH, Bolognese PA, Nishikawa M, McDonnell NB, Francomano CA |title=Syndrome of occipitoatlantoaxial hypermobility, cranial settling, and chiari malformation type I in patients with hereditary disorders of connective tissue |journal=Journal of Neurosurgery. Spine |volume=7 |issue=6 |pages=601–9 |date=December 2007 |pmid=18074684 |doi=10.3171/SPI-07/12/601 |doi-access=free}} such as Ehlers–Danlos syndrome{{cite web |title=Dr. Bland Discusses Chiari & EDS 4(10) |publisher=Conquerchiari.org |date=November 20, 2006 |url=http://www.conquerchiari.org/subs%20only/Volume%204/Issue%204(10)/Bland%20Connective%20Tissue%204(10).html |access-date=November 4, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20130625161132/http://www.conquerchiari.org/subs%20only/Volume%204/Issue%204%2810%29/Bland%20Connective%20Tissue%204%2810%29.html |archive-date=June 25, 2013}} and Marfan syndrome.

Chiari malformation is the most frequently used term for this set of conditions. The use of the term "Arnold–Chiari malformation" has fallen somewhat out of favor over time, although it is used to refer to the type II malformation. Current sources use "Chiari malformation" to describe its four specific types, reserving the term "Arnold–Chiari" for type II only.{{cite web |title=Chiari malformation |work=Dorlands Medical Dictionary |url=http://www.mercksource.com/pp/us/cns/cns_hl_dorlands_split.jsp?pg=/ppdocs/us/common/dorlands/dorland/nine/100011880.htm |url-status=dead |archive-url=https://web.archive.org/web/20090901131825/http://www.mercksource.com/pp/us/cns/cns_hl_dorlands_split.jsp?pg=%2Fppdocs%2Fus%2Fcommon%2Fdorlands%2Fdorland%2Fnine%2F100011880.htm |archive-date=September 1, 2009}} Some sources still use "Arnold–Chiari" for all four types.{{cite book |title=Case Based Pediatrics For Medical Students and Residents |chapter=Chapter XVIII.16. Developmental Brain Anomalies |chapter-url=http://www.hawaii.edu/medicine/pediatrics/pedtext/s18c16.html |author=Kaipo T. Pau |editor=Jeffrey K. Okamoto |display-editors=etal |url=http://www.hawaii.edu/medicine/pediatrics/pedtext/pedtext.html |url-status=live |archive-url=https://web.archive.org/web/20100528143255/http://www.hawaii.edu/medicine/pediatrics/pedtext/pedtext.html |archive-date=May 28, 2010}}

Chiari malformation type 1 emerges during skull and brain development, often without symptoms until late childhood or adulthood. In contrast, the pediatric forms include type 2 and type 3, which are present from birth, making them congenital conditions.{{Cite web |title=Chiari malformation - Symptoms and causes |url=https://www.mayoclinic.org/diseases-conditions/chiari-malformation/symptoms-causes/syc-20354010#:~:text=Chiari%20malformation%20type%201%20develops,which%20is%20known%20as%20congenital. |access-date=2025-05-06 |website=Mayo Clinic |language=en}}

Chiari malformation or Arnold–Chiari malformation should not be confused with Budd–Chiari syndrome,{{cite web |title=Code 453.0: Budd-Chiari Syndrome |work=2008 ICD-9-CM Diagnosis |url=http://www.icd9data.com/2008/Volume1/390-459/451-459/453/453.0.htm |url-status=live |archive-url=https://web.archive.org/web/20081205100343/http://www.icd9data.com/2008/Volume1/390-459/451-459/453/453.0.htm |archive-date=December 5, 2008}} a hepatic condition also named for Hans Chiari.

In Pseudo-Chiari Malformation, leaking of CSF may cause displacement of the cerebellar tonsils and similar symptoms sufficient to be mistaken for a Chiari I malformation.{{cite web |title=Spontaneous Spinal Cerebrospinal Fluid Leaks: Diagnosis |url=http://www.medscape.com/viewarticle/405623_2 |url-status=live |archive-url=https://web.archive.org/web/20111211080935/http://www.medscape.com/viewarticle/405623_2 |archive-date=December 11, 2011}}

While there is no current cure, the treatments for Chiari malformation are surgery and management of symptoms. Treatment is directed on the occurrence of clinical symptoms rather than the radiological findings. The presence of a syrinx is known to give specific signs and symptoms that vary from dysesthetic sensations to algothermal dissociation to spasticity and paresis. These are important indications that decompressive surgery is needed for patients with Chiari Malformation Type II. Type II patients have severe brainstem damage and rapidly diminishing neurological response.{{cite journal |vauthors=Imperato A, Seneca V, Cioffi V, Colella G, Gangemi M |title=Treatment of Chiari malformation: who, when and how |journal=Neurological Sciences |volume=32 |pages=S335-9 |date=December 2011 |issue=Suppl 3 |pmid=21822700 |doi=10.1007/s10072-011-0709-y |s2cid=7602738 |url=https://springerlink3.metapress.com/content/232275446662897m/resource-secured/?target=fulltext.pdf&sid=jlhep2yxgzlpur1fzhhnoovi |url-status=dead |archive-url=https://web.archive.org/web/20220515081437/https://springerlink3.metapress.com/content/232275446662897m/resource-secured/?target=fulltext.pdf&sid=jlhep2yxgzlpur1fzhhnoovi |archive-date=2022-05-15|url-access=subscription }}{{cite journal |vauthors=Klekamp J, Batzdorf U, Samii M, Bothe HW |title=The surgical treatment of Chiari I malformation |journal=Acta Neurochirurgica |volume=138 |issue=7 |pages=788–801 |year=1996 |pmid=8869706 |doi=10.1007/BF01411256 |s2cid=6777364}}

Decompressive surgery involves removing the lamina of the first and sometimes the second or third cervical vertebrae and part of the occipital bone of the skull to relieve pressure. The flow of spinal fluid may be augmented by a shunt. The surgery may involve the opening of the dura mater to allow decompression of the brain. A [https://www.conquerchiari.org/library/index/click/326#:~:text=sewn%20into%20the-,dura,replace%20or%20repair%20a%20defect dural graft] may be applied to cover the expanded posterior fossa. In those with type I Chiari malformations (especially those with a syrinx), a bone resection with duraplasty (compared to a bone resection without duraplasty) is associated with greater symptom relief and has a higher rate of symptomatic remission, and a lower need for re-operation. However, a bone resection with duraplasty was also associated with a higher rate of surgical complications.{{cite journal |last1=Tam |first1=SKP |last2=Brodbelt |first2=A |last3=Bolognese |first3=PA |last4=Foroughi |first4=M |title=Posterior fossa decompression with duraplasty in Chiari malformation type 1: a systematic review and meta-analysis. |journal=Acta Neurochirurgica |date=January 2021 |volume=163 |issue=1 |pages=229–238 |doi=10.1007/s00701-020-04403-9 |pmid=32577895}} Re-operation may be needed in up to 6.8% of patients, and possible causes of re-operation include incomplete decompression and dural scarring. Other complications that are possible in surgical repair of type I Chiari malformations include an aseptic meningitis due to irritation from the dural grafts which is seen in 32% of cases. Rates of aseptic meningitis are lower with dural allografts or autografts as compared to bovine or synthetic grafts. Another complication includes a CSF leak, which may occur in up to 21% of people post-operatively.

A small number of neurological surgeons{{who|date=July 2015}} believe that detethering the spinal cord as an alternate approach relieves the compression of the brain against the skull opening (foramen magnum), obviating the need for decompression surgery and associated trauma. However, this approach is significantly less documented in the medical literature, with reports on only a handful of patients. The alternative spinal surgery is also not without risk.{{citation needed|date=July 2015}}

Complications of decompression surgery can arise. They include bleeding, damage to structures in the brain and spinal canal, meningitis, CSF fistulas, occipito-cervical instability, and pseudomeningocele. Rare post-operative complications include hydrocephalus and brainstem compression by retroflexion of odontoid. Also, an extended CVD created by a wide opening and big duroplasty can cause a cerebellar "slump". This complication needs to be corrected by cranioplasty.

In certain cases, irreducible compression of the brainstem occurs from in front (anteriorly or ventral) resulting in a smaller posterior fossa and associated Chiari malformation. In these cases, an anterior decompression is required. The most commonly used approach is to operate through the mouth (transoral) to remove the bone compressing the brainstem, typically the odontoid. This results in decompressing the brainstem and therefore gives more room for the cerebellum, thus decompressing the Chiari malformation. Arnold Menzes, MD, is the neurosurgeon who pioneered this approach in the 1970s at the University of Iowa. Between 1984 and 2008 (the MR imaging era), 298 patients with irreducible ventral compression of the brainstem and Chiari type I malformation underwent a transoral approach for ventral cervicomedullary decompression at the University of Iowa. The results have been excellent resulting in improved brainstem function and resolution of the Chiari malformation in the majority of patients.{{Cite web |title=Arnold Menezes {{!}} Department of Neurosurgery |url=https://medicine.uiowa.edu/neurosurgery/profile/arnold-menezes |access-date=2025-05-06 |website=medicine.uiowa.edu}}

The incidence of congenital Chiari I malformation was previously believed to be in the range of one per 1000 births, but is likely much higher.{{cite web |title=Chiari Malformation Fact Sheet | National Institute of Neurological Disorders and Stroke |url=http://www.ninds.nih.gov/disorders/chiari/detail_chiari.htm |access-date=January 9, 2015 |url-status=live |archive-url=https://web.archive.org/web/20111027111506/http://www.ninds.nih.gov/disorders/chiari/detail_chiari.htm |archive-date=October 27, 2011}}{{full citation needed|date=July 2015}} Women are three times more likely than men to have a congenital Chiari malformation.{{cite web |title=The Chiari Center - WI Chiari Center |url=http://www.wichiaricenter.org/oth/Page.asp?PageID%3DOTH000006 |access-date=December 28, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20110704123740/http://www.wichiaricenter.org/oth/Page.asp?PageID=OTH000006 |archive-date=July 4, 2011}}{{full citation needed|date=July 2015}} Type II malformations are more prevalent in people of Celtic descent. A study using upright MRI found cerebellar tonsillar ectopia in 23% of adults with headache from motor-vehicle-accident head trauma. Upright MRI was more than twice as sensitive as standard MRI, likely because gravity affects cerebellar position.

Cases of congenital Chiari malformation may be explained by evolutionary and genetic factors.{{Cite journal |last1=Sivakumaran |first1=Priya |last2=Ashwood |first2=Neil |last3=Kamal |first3=Muhammad |last4=Jayakumar |first4=Nithish |last5=Sivakumaran |first5=Priya |last6=Ashwood |first6=Neil |last7=Kamal |first7=Muhammad |last8=Jayakumar |first8=Nithish |date=2023-10-19 |title=The Pathogenesis of Chiari Malformation and Syringomyelia: A Case Report and Systematic Review of Current Theories |journal=Cureus |language=en |volume=15 |issue=10 |pages=e47301 |doi=10.7759/cureus.47301 |doi-access=free |pmid=38022024 |pmc=10656570 |issn=2168-8184}} Typically, an infant's brain weighs around 400g at birth and triples to 1100-1400g by age 11. At the same time the cranium triples in volume from 500 cm³ to 1500 cm³ to accommodate the growing brain.Nolte J. The human brain: an introduction to its functional anatomy. Philadelphia: Mosby; 2002{{page needed|date=July 2015}} During human evolution, the skull underwent numerous changes to accommodate the growing brain. The evolutionary changes included increased size and shape of the skull, decreased basal angle and basicranial length. These modifications resulted in significant reduction of the size of the posterior fossa in modern humans. In normal adults, the posterior fossa comprises 27% of the total intracranial space, while in adults with Chiari Type I, it is only 21%.{{cite journal |vauthors=Furtado SV, Reddy K, Hegde AS |title=Posterior fossa morphometry in symptomatic pediatric and adult Chiari I malformation |journal=Journal of Clinical Neuroscience |volume=16 |issue=11 |pages=1449–54 |date=November 2009 |pmid=19736012 |doi=10.1016/j.jocn.2009.04.005 |s2cid=37527076}} H. neanderthalensis had platycephalic (flattened) skulls. Some cases of Chiari are associated with platybasia (flattening of the skull base).{{cite journal |vauthors=Sgouros S, Kountouri M, Natarajan K |title=Skull base growth in children with Chiari malformation Type I |journal=Journal of Neurosurgery |volume=107 |issue=3 Suppl |pages=188–92 |date=September 2007 |pmid=17918522 |doi=10.3171/PED-07/09/188}}

The history of Chiari malformation:

• 1883: Cleland was the first to describe Chiari II or Arnold–Chiari malformation on his report of a child with spina bifida, hydrocephalus, and anatomical alterations of the cerebellum and brainstem.{{cite journal |vauthors=Schijman E |title=History, anatomic forms, and pathogenesis of Chiari I malformations |journal=Child's Nervous System |volume=20 |issue=5 |pages=323–8 |date=May 2004 |pmid=14762679 |doi=10.1007/s00381-003-0878-y |s2cid=2735964}}
• 1891: Hans Chiari, a Viennese pathologist, described the case of a 17-year-old female with elongation of the tonsils into cone shaped projections which accompany the medulla and are crammed into the spinal canal.
• 1907: Schwalbe and Gredig, pupils of German pathologist Julius Arnold, described four cases of meningomyelocele and alterations in the brainstem and cerebellum, and gave the name "Arnold–Chiari" to these malformations.{{cite web |last1=Enersen |first1=Daniel |title=Julius Arnold |website=Whonamedit A dictionary of medical eponyms |url=http://www.whonamedit.com/doctor.cfm/280.html |access-date=February 4, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150204080738/http://www.whonamedit.com/doctor.cfm/280.html |archive-date=February 4, 2015}}
• 1932: Van Houweninge Graftdijk was the first to report the surgical treatment of Chiari malformations. All patients died from surgery or postoperative complications.
• 1935: Russell and Donald suggested that decompression of the spinal cord at the foramen magnum might facilitate the CSF circulation.
• 1940: Gustafson and Oldberg diagnosed Chiari malformation with syringomyelia.
• 1974: Bloch et al. described the tonsils position to be classified between 7 mm and 8 mm below cerebellum.
• 1985: Aboulezz used MRI for discovery of extension

The condition was brought to the mainstream on the series CSI: Crime Scene Investigation in the tenth-season episode "Internal Combustion" on February 4, 2010.{{cite web |title=CSI: Crime Scene Investigation–'Internal Combustion' |website=CSI Files |language=en-US |url=https://www.csifiles.com/content/2010/02/csi-crime-scene-investigation-internal-combustion/ |access-date=2023-03-28}}

• Rosanne Cash{{cite web |title=Rosanne Cash recovering from brain surgery – Entertainment – Celebrities |publisher=Today.com |date=October 26, 2011 |url=http://www.today.com/id/22220526 |access-date=November 4, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20151017080307/http://www.today.com/id/22220526 |archive-date=October 17, 2015}} – U.S. singer-songwriter; daughter of Johnny Cash
• Julia Clukey{{cite web |author=Julia Clukey |date=January 21, 2014 |title=Olympian: Brain disorder made me stronger |publisher=CNN |url=http://www.cnn.com/2014/01/15/health/human-factor-clukey/index.html |access-date=August 26, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150812131836/http://www.cnn.com/2014/01/15/health/human-factor-clukey/index.html |archive-date=August 12, 2015}} – U.S. luge competitor for Team USA in 2010 Vancouver Winter Olympics
• Joanna David{{cite news |title=We all make fantastic blunders... |work=The Daily Telegraph |date=September 18, 2006 |last1=Paton |first1=Maureen |url=https://www.telegraph.co.uk/culture/theatre/drama/3655402/We-all-make-fantastic-blunders.html |access-date=March 13, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150403071935/http://www.telegraph.co.uk/culture/theatre/drama/3655402/We-all-make-fantastic-blunders.html |archive-date=April 3, 2015}} – British television and stage actress
• J. B. Holmes{{cite web |date=22 August 2011 |title=J.B. Holmes to have brain surgery |website=espn.com |author=ESPN.com news services |access-date=24 November 2019 |url-status=live |url=https://www.espn.com/golf/story/_/id/6885794/jb-holmes-brain-surgery-week |archive-url=https://web.archive.org/web/20170708044442/http://www.espn.com/golf/story/_/id/6885794/jb-holmes-brain-surgery-week |archive-date=8 July 2017}} – U.S. professional golfer
• Marissa Irwin{{cite web |title=Marissa's story |publisher=The Chiari Institute and MedNet Technologies, Inc. |location=Great Neck, NY, U.S.A. |url=http://www.chiariinstitute.com/testimonials/MIrwin.pdf |access-date=August 26, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150906095528/http://www.chiariinstitute.com/testimonials/MIrwin.pdf |archive-date=September 6, 2015}} – U.S. fashion model with Chiari secondary to Ehlers–Danlos syndrome
• Bobby Jones{{cite web |title=Bobby Jones Society | Chiari & Syringomyelia Foundation |publisher=Csfinfo.org |url=http://www.csfinfo.org/bobby_jones_society |access-date=November 4, 2011 |url-status=live |archive-url=https://web.archive.org/web/20111007210642/http://www.csfinfo.org/bobby_jones_society |archive-date=October 7, 2011}} – U.S. World Golf Hall of Fame golfer and founder of the Augusta National Golf Club
• Allysa Seely – U.S. Gold Medalist at the 2016 Summer Paralympics in the paratriathlon{{cite web |title=Paratriathlete Allysa Seely on prosthetics and PRs |publisher=ESPN |date=July 5, 2016 |url=http://www.espn.com/espnw/sports/article/16745686/paratriathlete-allysa-seely-talks-prosthetics-prs-accomplishments-espn-body-issue |url-status=live |archive-url=https://web.archive.org/web/20170804214032/http://www.espn.com/espnw/sports/article/16745686/paratriathlete-allysa-seely-talks-prosthetics-prs-accomplishments-espn-body-issue |archive-date=August 4, 2017}}
• Leah Shapiro{{cite web |author=David Renshaw |date=October 18, 2014 |title=Black Rebel Motorcycle Club cancel LA gig as drummer undergoes brain surgery |work=NME |url=http://www.nme.com/news/black-rebel-motorcycle-club/80484 |access-date=August 26, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150925221221/http://www.nme.com/news/black-rebel-motorcycle-club/80484 |archive-date=September 25, 2015}} – U.S. drummer for the band Black Rebel Motorcycle Club
• Michelle Stilwell – Canadian wheelchair racer and politician{{cite web|author=Gary Kingston |date=May 31, 2008 |title=Lonely at the Top |work=The Vancouver Sun |url=http://www.canada.com/story.html?id=b0bf13ea-d410-4975-b477-febf1df5ec94 |access-date=August 27, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20151017080306/http://www.canada.com/story.html?id=b0bf13ea-d410-4975-b477-febf1df5ec94 |archive-date=October 17, 2015}}
• Rachid Taha{{cite news |title=Mort à 59 ans, Rachid Taha souffrait d'une maladie génétique – H24info |last=mjid |first=Safia |date=September 14, 2018 |work=H24info |language=fr-FR |url=https://www.h24info.ma/culture/mort-a-59-ans-rachid-taha-souffrait-dune-maladie-genetique/ |access-date=September 22, 2018}} – Algerian singer
• Sabre Norris – Australian skateboarder and surfer{{cite web |last=Cronshaw |first=Damon |date=January 30, 2018 |title=Sabre Norris shares her story about her health and medical condition |website=Newcastle Herald |url=https://www.newcastleherald.com.au/story/5197651/updated-siblings-give-cuddles-to-ease-the-tears-of-sabre-norris/ |access-date=21 April 2021 |url-status=live |archive-url=https://web.archive.org/web/20210828030442/https://www.newcastleherald.com.au/story/5197651/updated-siblings-give-cuddles-to-ease-the-tears-of-sabre-norris/ |archive-date=August 28, 2021}}

{{Portal|Medicine}}

• Hypermobility spectrum disorder

{{Notelist}}

{{Reflist}}

{{Medical resources

| DiseasesDB = 899

| ICD10 = {{ICD10|Q|07|0|q|00}}

| ICD9 = {{ICD9|348.4}},{{ICD9|741.0}}

| ICDO =

| OMIM = 207950

| MedlinePlus =

| eMedicineSubj = article

| eMedicineTopic = 1483583

| MeshID = D001139

}}

{{Congenital malformations and deformations of nervous system}}

Category:Congenital disorders of nervous system

Category:Diseases named after discoverers