Arnold-Chiari, or simply Chiari, malformation is the name given to a group of deformities of the posterior fossa and hindbrain (cerebellum, pons, and medulla oblongata). Issues range from cerebellar tonsillar herniation through the foramen magnum to the absence of the cerebellum with or without other associated intracranial or extracranial defects such as hydrocephalus, syrinx, encephalocele or spinal dysraphism.
Chiari malformations are classified based on their morphology and severity of anatomic defects, typically through imaging (or autopsy).
Chiari I is the least severe, and often found incidentally. It is characterized by one or both pointed (not rounded) cerebellar tonsils that project 5 mm below the foramen magnum, measured by a line drawn from the basion to the opisthion (McRae Line).
Chiari II consists of brainstem herniation and a towering cerebellum in addition to the herniated cerebellar tonsils and vermis due to an open distal spinal dysraphism/myelomeningocele.
Chiari III involves herniation of the hindbrain (cerebellum with or without the brainstem) into a low occipital or high cervical meningoencephalocele.
Chiari IV is now considered obsolete. Prior to becoming an obsolete diagnosis, it was already a more controversial and rare variant that demonstrated severe cerebellar hypoplasia, similar to primary cerebellar agenesis. Previously some stated that myelomeningocele could be present, while others argued that the presence of myelomeningocele should then be classified as a Chiari II with a vanishing cerebellum.
There are other controversial reported classifications including Chiari 0, Chiari 1.5, and Chiari V. Chiari 0 is characterized by syringomyelia without hindbrain herniation, while Chiari 1.5 is felt to be the progression of Chiari I with increased cerebellar tonsillar descent and some involvement of the brainstem. Chiari V, the most severe variant, represents cerebellar agenesis with occipital lobe descent and herniation through the foramen magnum.
There are multiple proposed theories including molecular, hydrodynamic, and mechanical, with the likelihood that different mechanisms can have the same resulting Chiari malformation.
Reduced volume of the posterior fossa leads to displacement of the cerebellar tonsils through the foramen magnum in Chiari I malformations. Causes include primary congenital hypoplasia or secondarily from acquired morphologic changes, such as premature closure of sutures, calvarial dysplasia, or genetic/syndromic. Mutations on chromosomes 1 and 22 have been identified as possible causes for hereditary posterior fossa hypoplasia.
McClone and Knepper proposed that an open neural tube defect (myelomeningocele) is the underlying cause of Chiari II malformations. This leads to leakage or redirected flow of cerebrospinal fluid resulting in a fourth ventricle that is unable to maintain distension. This continued collapse of the fourth ventricle in utero results in a hypoplastic posterior fossa and cerebellar tonsillar herniation. This is also the suspected cause of Chiari III as well, though in the setting of an encephalocele or high cervical myelomeningocele, as opposed to the lumbar/sacral myelomeningocele in Chiari II. Folate deficiency and methylenetetrahydrofolate reductase mutations increase the risk of neural tube defects and can thus be an underlying cause of Chiari II and III.
The etiology of the remaining Chiari variants is still debated and not clearly known. Trauma can be an etiology of cerebellar tonsillar herniation, though, in the setting of a normal-sized posterior fossa, a designation of Chiari is not appropriate.
Chiari II occurs in 0.44/1000 births without gender predominance but can have a decreased incidence with folate replacement therapy by the mother in utero.
The remaining Chiari malformations are much rarer. Of these other variants, Chiari III is the most common, consisting of 1-4.5% of all Chiari malformations.
Neurologic signs and symptoms can arise from 2 mechanisms:
In patients with the Chiari I malformation, the bones of the skull base often are underdeveloped, which results in a reduced volume of the posterior fossa, the volume of which is inadequate to contain the entire cerebellum, thus cerebellar tonsils are displaced through the foramen magnum.
The posterior fossa in Chiari type II malformation is even smaller than in Chiari I malformation. The cerebrospinal fluid (CSF) cisterns are poorly developed due to lack of fourth ventricular expansion as a consequence of in-utero derivation of CSF circulation to the neural tube defect, all of which results in hindbrain structures downward herniating with subsequent compression of these structures against the foramen magnum.
In both type I and II, there is CSF-flow obstruction by the foramen magnum crowding, and consequently, hydrocephalus and/or syringomyelia formation are possible over time.
In Chiari I malformation the most common presentation is suboccipital headaches and/or neck pain (80%). Symptoms are exacerbated when asked to perform the Valsalva maneuver. Other common presentations include ocular disturbances, otoneurologic symptoms (dizziness, hearing loss, vertigo), gait ataxia, and generalized fatigue. Although much less common, the literature reports multiple case studies in which patients have presented with isolated extremity pain or weakness, one such report including a presentation of unilateral shoulder pain with isolated muscle weakness presenting to a sports medicine clinic.
Cerebellar signs, including ataxia, dysmetria, and nystagmus, and lower cranial nerve deficits (IX, X, XI, XII CN) result either from direct compression of the cerebellum or medulla at the foramen magnum or from syringomyelia or syringobulbia.
Sleep apnea can occur in a patient with Chiari malformation due to a weakness of pharyngeal muscles elicited by the brainstem, upper spinal cord, or lower cranial nerve compression.
It is not an uncommon scenario to find patients with radiological findings compatible with Chiari malformation with no clinical manifestations of the disease (incidental Chiari malformation). Therefore, nonspecific symptoms such as generalized fatigue or classic pattern migraines are not necessarily related to the Chiari malformation.
The remaining variants (with the exception of Chiari 0 and 1.5) are diagnosed often in utero or at birth.
Imaging evaluation of Chiari malformations varies, with Chiari I evaluated using magnetic resonance imaging (MRI) typically in a child or adult, whereas Chiari II-IV are often first evaluated by ultrasound in utero, with fetal MRI assessment performed for further characterization.
MRI of the head and cervical spine is the test of choice in evaluating Chiari I. This will demonstrate cerebellar tonsillar descent greater than 5 mm below the foramen magnum (McRae Line). In addition, a decreased size of the posterior fossa and a syrinx may be seen. Depending on the extent of the syrinx, the addition of a thoracic and/or lumbar spine MRI may be needed. In the setting of ventricular dilation, CSF flow (or cine) sequences may be performed to assess for CSF flow dynamics and evaluate for obstruction at the foramen magnum.
Other useful tests in the management of patients with Chiari I malformation include:
Fetal sonography, often during the second-trimester anatomy scan demonstrates the typical imaging features of Chiari II/III malformations. One classic imaging finding on ultrasound is the lemon sign of the anterior frontal calvarium, with loss of the normal convex curvature and flattening or inward bowing/scalloping that results in a shape similar to a lemon. The banana sign is another classic sign of Chiari II and distal neural tube defect, this time regarding the cerebellum, which demonstrates an abnormal morphology with anterior curvature of the cerebellum and obliteration of the cisterna magna. Chiari III will demonstrate the occipital or high cervical meningoencephalocele when evaluating the posterior fossa during a prenatal exam.
Fetal MRI can demonstrate the cerebellar hypoplasia/aplasia of Chiari IV/V, and further evaluates the neural tube defects and hindbrain herniation of Chiari II/III. MRI also better demonstrates the tectal beaking that occurs in Chiari II.
Laboratory studies are not of help in the evaluation of patients with Chiari malformation. However, laboratory studies are needed during planning for surgery. Routine studies like the complete blood count (CBC), coagulation profile, electrolyte levels, chest X-ray, and electrocardiogram (ECG) will suffice.
Patients with Chiari malformation and who have no symptoms can be managed medically. Headaches and neck pain can be treated with muscle relaxants, NSAIDs, and temporary use of a cervical collar. However, studies show that while a headache and nausea may improve, in many symptomatic patients there will be no improvement in gait with medical management. Close to 90% of patients with Chiari type I may remain asymptomatic even if they have syringomyelia.
The main treatment for Chiari malformation is surgical with the goal of re-establishing the CSF flow across the craniovertebral junction and relieving pressure on the cerebellum and hindbrain by decompressing the posterior fossa.
Surgery is recommended for persistently symptomatic patients and confirmed tonsillar herniation. In the setting of asymptomatic tonsillar herniation, with or without syrinx, observation is recommended, unless symptoms develop.
Better surgical results are seen when surgery is performed within 2 years of symptoms onset.
The standard surgical technique for Chiari I is a posterior fossa decompression. This is obtained by a suboccipital craniectomy enlarging the foramen magnum, often in conjunction with C1, and possible C2, laminectomy. The dura may or may not be opened, with subsequent dissection of arachnoid adhesions if present. Depending on the available dural expansion and size of the posterior fossa, a duraplasty may need to be performed. The dural graft can be an autograft such as occipital fascia or tensor fascia lata (TFL) tendon, or artificial dura. In the setting of a syrinx, a shunt can also be placed if decompression alone is not effective. Tonsillar cauterization may also be performed.
More recently, minimally invasive techniques have been described similar to those used in the spine. These allow for smaller incisions, less soft tissue damage, less dural manipulation, shorter hospital stays, faster recovery, and fewer complications.
Initial surgical correction for Chiari II is the correction of the myelomeningocele, generally in the first 48 hours. This can also be done in utero through a hysterotomy. Closure of the spinal dysraphism can be done in a variety of ways, with either primary skin closure, myocutaneous flap, or fasciocutaneous flap, depending on the severity, involved layers, and the available adjacent tissue. The vast majority will eventually need a ventricular shunt for CSF diversion in the setting of hydrocephalus. If needed, a posterior decompression is performed later to allow suboccipital expansion.
Chiari III follows a similar course to Chiari II. The occipital/high cervical encephalocele is corrected first, with resection of herniated contents, as these are typically non-viable, followed by dural closure and a cranioplasty. If the amount of herniated tissue is greater than intracranial contents, then the patient is deemed a nonsurgical candidate. A ventricular shunt is placed if the patient has concomitant hydrocephalus.
Contraindications to Surgery
Suboccipital decompression is contraindicated when the tonsillar herniation is due to a pathology other than Chiari malformation. Some examples of this are intracranial hypotension or mass effect in the posterior fossa due to a mass.
Chiari I has a good prognosis, but it also depends on the presence of preexisting neurological deficits. Most patients who have no neurological deficits have an excellent outcome. Chiari II has a 3% neonatal in-hospital mortality, and 15% 3-year mortality rate. Those that survive can have increasing motor dysfunction over time. Continued follow-up for shunt placement evaluation or shunt failure is recommended. Prognosis in the more severe Chiari variants is poor and often dismal, with early death.
Individuals who have chronic weakness or gait problems usually do not improve and their prognosis is guarded.
In the postoperative period, monitoring for CSF leak is vital. Some patients may develop a pseudomeningocele, which may require drainage.
Patients can also be evaluated postoperatively with the Chicago Chiari Outcome Scale for a more subjective evaluation of postoperative improvement. This scoring system factors pain, non-pain symptoms, functionality and postoperative complications into a 1-4 point scale for each component. This results in a total score ranging from 4-16, with 4 representing an incapacitated outcome, while 16 represents an excellent outcome.
Exercise and heavy lifting should not be done for at least 3 to 4 weeks after the procedure.
Most patients require 6 to 8 weeks to recover from surgery and reverse any major neurological deficit fully. Patients should consider refraining from contact sports following surgery, even after the surgical site is well healed.
Repeat MRI is necessary to ensure that the syrinx has responded to the treatment.
If the Chiari I is being managed conservatively, the patient should be instructed to come back if he/she develops cough headaches or progressive limb weakness. In the postoperative period, the patient should be conscious of the risk of developing pseudomeningocele, CSF leak, and meningitis.
Arnold-Chiari, also known as Chiari malformation, is the name given to a group of deformities of the hindbrain (cerebellum, pons, and medulla oblongata).
Issues range from herniation of the posterior fossa contents outside of the cranial cavity to the absence of the cerebellum with or without other associated intracranial or extracranial defects such as hydrocephalus, syrinx, encephalocele or spinal dysraphism.
For Chiari I malformation, the prognosis is good, but it also depends on the presence of preexisting neurological deficits. Most patients who have no neurological deficits have an excellent outcome.
A controversial subject in clinical management entails the diagnosis in the setting of possible sport-specific participation. Historically, symptomatic and postsurgical Chiari I patients were advised to not return to contact sports, but recent studies have shown that the risk of catastrophic injury in this population is low. Regardless, a decision should be made on a case by case basis.
Individuals who have chronic weakness or gait problems usually do not improve, and their prognosis is guarded.
Arnold Chiari malformations are relatively common and represent a spectrum of hindbrain anomalies. Depending on the severity of the malformation, the individual may be asymptomatic or have severe neurological symptoms. While the patients are often managed with decompressive surgery, the nurses are responsible for looking after these individuals. Hence, the nurse must be aware of the potential post-surgical complications and their presentation. The prognosis for most patients with a Chiari I malformation is good, but it also depends on the initial neurological presentation. Those patients with mild neurological deficits tend to have good outcomes, but those with moderate to severe symptoms tend to have a guarded prognosis. The surgery is also associated with several complications of which the most common are CSF leak and pseudomeningocele. A few individuals may have a persistent syrinx and may require a shunt. (Level III)
|||de Arruda JA,Figueiredo E,Monteiro JL,Barbosa LM,Rodrigues C,Vasconcelos B, Orofacial clinical features in Arnold Chiari type I malformation: A case series. Journal of clinical and experimental dentistry. 2018 Apr [PubMed PMID: 29750100]|
|||Bhimani AD,Esfahani DR,Denyer S,Chiu RG,Rosenberg D,Barks AL,Arnone GD,Mehta AI, Adult Chiari I Malformations: An Analysis of Surgical Risk Factors and Complications Using an International Database. World neurosurgery. 2018 Jul [PubMed PMID: 29684513]|
|||Kandeger A,Guler HA,Egilmez U,Guler O, Major depressive disorder comorbid severe hydrocephalus caused by Arnold-Chiari malformation. Indian journal of psychiatry. 2017 Oct-Dec [PubMed PMID: 29497204]|
|||Arora R, Imaging spectrum of cerebellar pathologies: a pictorial essay. Polish journal of radiology. 2015; [PubMed PMID: 25806100]|
|||Cama A,Tortori-Donati P,Piatelli GL,Fondelli MP,Andreussi L, Chiari complex in children--neuroradiological diagnosis, neurosurgical treatment and proposal of a new classification (312 cases). European journal of pediatric surgery : official journal of Austrian Association of Pediatric Surgery ... [et al] = Zeitschrift fur Kinderchirurgie. 1995 Dec; [PubMed PMID: 8770577]|
|||Hadley DM, The Chiari malformations. Journal of neurology, neurosurgery, and psychiatry. 2002 Jun; [PubMed PMID: 12122202]|
|||Iskandar BJ,Hedlund GL,Grabb PA,Oakes WJ, The resolution of syringohydromyelia without hindbrain herniation after posterior fossa decompression. Journal of neurosurgery. 1998 Aug; [PubMed PMID: 9688115]|
|||Kim IK,Wang KC,Kim IO,Cho BK, Chiari 1.5 malformation : an advanced form of Chiari I malformation. Journal of Korean Neurosurgical Society. 2010 Oct; [PubMed PMID: 21113370]|
|||Tubbs RS,Muhleman M,Loukas M,Oakes WJ, A new form of herniation: the Chiari V malformation. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery. 2012 Feb; [PubMed PMID: 22038152]|
|||Giammattei L,Borsotti F,Parker F,Messerer M, Chiari I malformation: surgical technique, indications and limits. Acta neurochirurgica. 2018 Jan [PubMed PMID: 29130121]|
|||Markunas CA,Enterline DS,Dunlap K,Soldano K,Cope H,Stajich J,Grant G,Fuchs H,Gregory SG,Ashley-Koch AE, Genetic evaluation and application of posterior cranial fossa traits as endophenotypes for Chiari type I malformation. Annals of human genetics. 2014 Jan; [PubMed PMID: 24359474]|
|||McLone DG,Knepper PA, The cause of Chiari II malformation: a unified theory. Pediatric neuroscience. 1989; [PubMed PMID: 2699756]|
|||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. 2015 Feb; [PubMed PMID: 25479580]|
|||Langridge B,Phillips E,Choi D, Chiari Malformation Type 1: A Systematic Review of Natural History and Conservative Management. World neurosurgery. 2017 Aug [PubMed PMID: 28435116]|
|||Dlouhy BJ,Dawson JD,Menezes AH, Intradural pathology and pathophysiology associated with Chiari I malformation in children and adults with and without syringomyelia. Journal of neurosurgery. Pediatrics. 2017 Dec [PubMed PMID: 29027876]|
|||Zhang D,Melikian R,Papavassiliou E, Chiari I Malformation Presenting as Shoulder Pain, Weakness, and Muscle Atrophy in a Collegiate Athlete. Current sports medicine reports. 2016 Jan-Feb [PubMed PMID: 26745162]|
|||Rogers JM,Savage G,Stoodley MA, A Systematic Review of Cognition in Chiari I Malformation. Neuropsychology review. 2018 Jun [PubMed PMID: 29468516]|
|||Jayamanne C,Fernando L,Mettananda S, Chiari malformation type 1 presenting as unilateral progressive foot drop: a case report and review of literature. BMC pediatrics. 2018 Feb 7 [PubMed PMID: 29415676]|
|||Klekamp J, How Should Syringomyelia be Defined and Diagnosed? World neurosurgery. 2018 Mar [PubMed PMID: 29317358]|
|||Thomas M, The lemon sign. Radiology. 2003 Jul; [PubMed PMID: 12832584]|
|||Nicolaides KH,Campbell S,Gabbe SG,Guidetti R, Ultrasound screening for spina bifida: cranial and cerebellar signs. Lancet (London, England). 1986 Jul 12; [PubMed PMID: 2425202]|
|||Lin W,Duan G,Xie J,Shao J,Wang Z,Jiao B, Comparison of Results Between Posterior Fossa Decompression with and without Duraplasty for the Surgical Treatment of Chiari Malformation Type I: A Systematic Review and Meta-Analysis. World neurosurgery. 2018 Feb [PubMed PMID: 29138073]|
|||Rocque BG,Oakes WJ, Surgical Treatment of Chiari I Malformation. Neurosurgery clinics of North America. 2015 Oct; [PubMed PMID: 26408062]|
|||Sabba MF,Renor BS,Ghizoni E,Tedeschi H,Joaquim AF, Posterior fossa decompression with duraplasty in Chiari surgery: A technical note. Revista da Associacao Medica Brasileira (1992). 2017 Nov [PubMed PMID: 29451656]|
|||Chen J,Li Y,Wang T,Gao J,Xu J,Lai R,Tan D, Comparison of posterior fossa decompression with and without duraplasty for the surgical treatment of Chiari malformation type I in adult patients: A retrospective analysis of 103 patients. Medicine. 2017 Jan; [PubMed PMID: 28121938]|
|||Grasso G,Torregrossa F, Minimally Invasive Surgery for Decompression in Chiari I Malformation. World neurosurgery. 2019 Aug; [PubMed PMID: 31121366]|
|||Kotil K,Ozdogan S,Kayaci S,Duzkalir HG, Long-Term Outcomes of a New Minimally Invasive Approach in Chiari Type 1 and 1.5 Malformations: Technical Note and Preliminary Results. World neurosurgery. 2018 Jul; [PubMed PMID: 29698796]|
|||Pakzaban P, Technique for Mini-open Decompression of Chiari Type I Malformation in Adults. Operative neurosurgery (Hagerstown, Md.). 2017 Aug 1; [PubMed PMID: 28838117]|
|||Quillo-Olvera J,Navarro-Ramírez R,Quillo-Olvera D,Quillo-Reséndiz J,Kim JS, Minimally Invasive Craniocervical Decompression for Chiari 1 Malformation: An Operative Technique. Journal of neurological surgery. Part A, Central European neurosurgery. 2019 Jul; [PubMed PMID: 31018228]|
|||Zagzoog N,Reddy KK, Use of Minimally Invasive Tubular Retractors for Foramen Magnum Decompression of Chiari Malformation: A Technical Note and Case Series. World neurosurgery. 2019 Aug; [PubMed PMID: 31048052]|
|||Hu Y,Liu J,Chen H,Jiang S,Li Q,Fang Y,Gong S,Wang Y,Huang S, A minimally invasive technique for decompression of Chiari malformation type I (DECMI study): study protocol for a randomised controlled trial. BMJ open. 2015 Apr 29; [PubMed PMID: 25926152]|
|||Adzick NS,Thom EA,Spong CY,Brock JW 3rd,Burrows PK,Johnson MP,Howell LJ,Farrell JA,Dabrowiak ME,Sutton LN,Gupta N,Tulipan NB,D'Alton ME,Farmer DL, A randomized trial of prenatal versus postnatal repair of myelomeningocele. The New England journal of medicine. 2011 Mar 17; [PubMed PMID: 21306277]|
|||Messing-Jünger M,Röhrig A, Primary and secondary management of the Chiari II malformation in children with myelomeningocele. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery. 2013 Sep; [PubMed PMID: 24013325]|
|||Işik N,Elmaci I,Silav G,Celik M,Kalelioğlu M, Chiari malformation type III and results of surgery: a clinical study: report of eight surgically treated cases and review of the literature. Pediatric neurosurgery. 2009; [PubMed PMID: 19221459]|
|||Goel A,Gore S,Shah A,Dharurkar P,Vutha R,Patil A, Atlantoaxial Fixation for Chiari 1 Formation in Pediatric Age-Group Patients: Report of Treatment in 33 Patients. World neurosurgery. 2018 Mar [PubMed PMID: 29294396]|
|||Martinez-Sabater A,Ballestar-Tarin ML,Vazquez-Seoane M,Mari-Avargues L,Saus-Ortega C,Del Carmen Casal-Angulo M, Quality of Life in Individuals Affected by Arnold Chiari Malformation: Comparison and Validation of a Measurement Instrument. Endocrine, metabolic [PubMed PMID: 29173189]|
|||Aliaga L,Hekman KE,Yassari R,Straus D,Luther G,Chen J,Sampat A,Frim D, A novel scoring system for assessing Chiari malformation type I treatment outcomes. Neurosurgery. 2012 Mar; [PubMed PMID: 21849925]|
|||Yarbrough CK,Greenberg JK,Smyth MD,Leonard JR,Park TS,Limbrick DD Jr, External validation of the Chicago Chiari Outcome Scale. Journal of neurosurgery. Pediatrics. 2014 Jun; [PubMed PMID: 24724715]|
|||Gilmer HS,Xi M,Young SH, Surgical Decompression for Chiari Malformation Type I: An Age-Based Outcomes Study Based on the Chicago Chiari Outcome Scale. World neurosurgery. 2017 Nov; [PubMed PMID: 28804039]|
|||Strahle J,Geh N,Selzer BJ,Bower R,Himedan M,Strahle M,Wetjen NM,Muraszko KM,Garton HJ,Maher CO, Sports participation with Chiari I malformation. Journal of neurosurgery. Pediatrics. 2016 Apr; [PubMed PMID: 26636249]|
|||Meehan WP 3rd,Jordaan M,Prabhu SP,Carew L,Mannix RC,Proctor MR, Risk of athletes with Chiari malformations suffering catastrophic injuries during sports participation is low. Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine. 2015 Mar; [PubMed PMID: 24905537]|
|||Lei ZW,Wu SQ,Zhang Z,Han Y,Wang JW,Li F,Shu K, Clinical Characteristics, Imaging Findings and Surgical Outcomes of Chiari Malformation Type I in Pediatric and Adult Patients. Current medical science. 2018 Apr [PubMed PMID: 30074187]|