BASICS
DESCRIPTION
- Chiari disorders involve the cerebellum and craniocervical junction and include alteration of CSF hemodynamics and herniation of the cerebellar tonsils into the spinal canal.
- There are three commonly described entities:
- Chiari I malformations:
- Herniation of the cerebellar tonsils >5 mm below the foramen magnum
- Associated with syringomyelia (1)
- Hydrocephalus is uncommon and constrictive.
- Chiari II malformations ("classic"):
- Variable descent of cerebellar tonsils and brainstem into spinal canal
- Aqueduct and 4th ventricle elongation associated with spina bifida and myelomeningocele (2)
- Hydrocephalus in 70% of cases is obstructive or constrictive in nature.
- Chiari III malformations (rare):
- Small posterior fossa with an associated encephalocele containing the cerebellar structures
- Hydrocephalus in 50% of cases due to obstruction
- Chiari IV (very rare)
- Primary cerebellar agenesis
EPIDEMIOLOGY
Prevalence
- True incidence is estimated at 1 to 5 in 1,000.
- Female to male 3:2 (1)
- Chiari I malformations may present at any age and normally do not become clinically apparent until adolescence or adulthood.
- MRI has led to an increase in the diagnosis of asymptomatic Chiari I malformations.
- Chiari I and II malformations are typically discovered during prenatal testing due to the associated neural tube defects (NTDs) (2).
ETIOLOGY AND PATHOPHYSIOLOGY
- Several models describe Chiari malformations currently. Evidence does not support one over another.
- The crowding theory implicates restricted volume in the posterior cranial fossa forcing the cerebellum through the foramen magnum.
- The oligo-cerebrospinal fluid theory suggests that insufficient cerebrospinal fluid (CSF) leads to a smaller posterior fossa due to reduced hydrostatic forces.
- Although there is no clear inheritance yet identified, a simple genetic malformation may also cause aberrant cerebellar growth.
RISK FACTORS
Maternal folate deficiency is a proposed (but unproven) risk factor.
GENERAL PREVENTION
Folic acid supplementation in women of childbearing years may prevent Arnold-Chiari malformations.
COMMONLY ASSOCIATED CONDITIONS
5.4-8.6% of patients with Chiari I malformations have NF1 (2).
DIAGNOSIS
HISTORY
- Depending on the specific malformation, typical symptoms include headache, tinnitus, vertigo, nausea, weakness, dysphagia, neck pain, and dysesthesia.
- Chiari I: These lesions cause symptoms because of two mechanisms.
- Direct compression of neural structures and alteration of CSF flow due to constriction of the aqueduct:
- Occipital headache
- Cranial nerve dysfunction
- When complicated with syringomyelia
- Most common presenting symptom is pain, which can be headache (occipital and worsened by Valsalva), back pain, shoulder pain, and arm pain.
- Can have a painful and intensifying left curving scoliosis
- Chiari II
- Because of the associated myelomeningocele, Chiari II malformations are typically detected by prenatal testing.
- CHIARI III
- These lesions are very rare and are typically identified before birth during routine prenatal testing.
PHYSICAL EXAM
- Examination should consist of a focused general medical exam and a complete neurologic exam.
- Neurologic exam should help with localization.
- Exam may reveal cranial nerve deficit or signs of brainstem or cerebellar involvement.
DIFFERENTIAL DIAGNOSIS
Differential diagnosis is primarily identifying the type of Arnold-Chiari malformation based on radiographic appearance.
DIAGNOSTIC TESTS & INTERPRETATION
- Chiari malformations are best defined neuroanatomically with MRI and CT. MRI is best for diagnosing the malformations; CT is best for finding associated bony abnormalities (2)[A].
- Rule out tumors and hydrocephalus as cause for the herniation.
- In general, cerebellar tonsils should not herniate farther than 3 mm below the basion-opisthion line:
- Herniations below 5 mm are pathologic.
- Between 3 and 5 mm are indeterminate, but can be pathologic if associated with neuroradiologic findings
- For infants and toddlers, a distance of 6 mm is pathologic.
- Affected individuals occasionally have a smaller posterior fossa volume:
- These individuals are more likely to present with clinical manifestations.
- These patients also have an improved response to cranial fossa decompression.
- Imaging the spinal cord should rule out syringomyelia:
- Sagittal and axial T1 images are required-small syrinxes may not be appreciated on sagittal cuts.
- Will be seen as low-intensity cavities within the spinal cord isointense with CSF on T1
- Associated anomalies (best defined by CT):
- Congenital
- Klippel-Feil anomaly
- Atlanto-occipital assimilation
- Platybasia
- Acquired
- Basilar invagination
- Craniofacial dysostosis
TREATMENT
MEDICATION
Neuropathic pain may be managed with anticonvulsants and antidepressants in addition to traditional pain medications.
- Anticonvulsants for neuropathic pain (off-label) (2)[A]
- Gabapentin 300 to 3,600 mg/day
- Pregabalin 75 to 150 mg twice daily
- Antidepressants for neuropathic pain (off-label) (2)[A]
- Amitriptyline 25 to 50 mg at bedtime
- Duloxetene 30 to 60 mg daily
- Venlafaxine 37.5 to 150 mg twice daily
ADDITIONAL THERAPIES
- Physical therapy (PT)/occupational therapy (OT) to treat chronic neck pain and headaches, to increase mobility and strength of extremities, and improve functionality and allow for performance of activities of daily living (2)[A]
- Speech therapy to improve phonation and articulation of speech secondary to cranial nerve dysfunction (2)[A]
- Craniosacral osteopathy to eliminate the restrictions to normal CSF flow using interventions on the craniosacral axis to minimize symptoms and improve the quality of life of the patient (2)[A]
SURGERY/OTHER PROCEDURES
- Surgery aims to correct the altered neuroanatomy and decompress hydrocephalus or syringomyelia.
- Expansion of the posterior fossa volume, and restoration of normal CSF dynamics
- A prospective 1-year study of 50 patient with suboccipital decompression to treat Chiari I malformation yielded a 66% improvement in pain, disability, general health, and quality of life at 1 year. With the major complication being development of a postoperative pseudomeningocele and CSF leaks (18% and 8%) (3)[B]
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
- Admit to neurosurgery for surgical correction if presenting with acute neurologic symptoms.
- Uncontrolled symptoms from acute hydrocephalus or syringomyelia may require hospitalization.
- If clinically stable at diagnosis, may be admitted for elective surgical correction based on the severity of symptoms
Nursing
Requires frequent assessment of neurologic function in the immediate postoperative period
Discharge Criteria
Discharge once neurologically stable.
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Follow-up with neurosurgery after hospital discharge.
Patient Monitoring
- Cerebellar tonsils ascend with age. Some lesions presumably resolve spontaneously as children age (4)[C].
- Radiologic follow-up with MRI every 1 to 2 years after surgical resection (1)[A],(4)[C]
- Close observation and radiologic surveillance every 3 to 12 months if surgery is deferred at diagnosis (4)[C].
DIET
No dietary restrictions
PATIENT EDUCATION
- The Chiari and Syringomyelia Foundation provides education and advocacy: www.csfinfo.org/
- Patient should be educated about symptoms and warning signs of hydrocephalus and syringomyelia.
PROGNOSIS
- Chiari I
- Highly variable-depends on the degree of herniation and CSF flow interruption. Those affected may never have symptoms, and some herniations may even resolve spontaneously as cerebellar tonsils ascend with age.
- Asymptomatic and mildly symptomatic patients often remain stable.
- Chiari II
- Varied; prognosis correlates with severity of symptoms
- Chiari III
- Very poor prognosis, most will not survive the neonatal period due to respiratory failure, and those who do will have severe mental retardation and neurologic deficits.
COMPLICATIONS
- Hydrocephalus
- Uncommon in Chiari I, but common in II and III
- Syringomyelia
- Cavitary dilation of the spinal cord
- Presence justifies neurosurgical consultation to consider surgical decompression, independent of the existence of symptoms
REFERENCES
11 Cheng JS, Nash J, Meyer GA. Chiari type I malformation revisited: diagnosis and treatment. Neurologist. 2002;8(6):357-362.22 Fern ”ndez AA, Guerrero AI, Mart nez MI, et al. Malformations of the craniocervical junction (Chiari type I and syringomyelia: classification, diagnosis and treatment). BMC Musculoskelet Disord. 2009;10(Suppl 1):S1.33 Parker SL, Godil SS, Zuckerman SL, et al. Comprehensive assessment of 1-year outcomes and determination of minimum clinically important difference in pain, disability, and quality of life after suboccipital decompression for Chiari malformation I in adults. Neurosurgery. 2013;73(4):569-581.44 Calderelli M, Di Rocco C. Diagnosis of Chiari I malformation and related syringomyelia: radiological and neurophysiological studies. Childs Nerv Syst. 2004;20(5):332-335.
ADDITIONAL READING
- Litvack ZN, Lindsay RA, Selden NR. Dura splitting decompression for Chiari I malformation in pediatric patients: clinical outcomes, healthcare costs, and resource utilization. Neurosurgery. 2013;72(6):922-929.
- Schijman E. History, anatomic forms, and pathogenesis of Chiari I malformations. Childs Nerv Syst. 2004;20(5):323-328.
- Shaffer N, Martin BA, Rocque B, et al. Cerebrospinal fluid flow impedance is elevated in type I Chiari malformation. J Biomech Eng. 2014;136(2):021012.
- Sun PP, Harrop J, Sutton LN, et al. Complete spontaneous resolution of childhood Chiari I malformation and associated syringomyelia. Pediatrics. 2001;107(1):182-184.
- Tubbs RS, Rutledge SL, Kosentka A, et al. Chiari I malformation and neurofibromatosis type 1. Pediatr Neurol. 2004;30(4):278-280.
- Vachha B, Adams RC, Rollins NK. Limbic tract anomalies in pediatric myelomeningocele and Chiari II malformation: anatomic correlations with memory and learning-initial investigation. Radiology. 2006;240(1):194-202.
CODES
ICD10
- Q07.00 Arnold-Chiari syndrome without spina bifida or hydrocephalus
- Q07.02 Arnold-Chiari syndrome with hydrocephalus
- Q07.01 Arnold-Chiari syndrome with spina bifida
- Q07.03 Arnold-Chiari syndrome with spina bifida and hydrocephalus
- Q04.8 Other specified congenital malformations of brain
- Q01.9 Encephalocele, unspecified
ICD9
- 348.4 Compression of brain
- 741.00 Spina bifida with hydrocephalus, unspecified region
- 742.0 Encephalocele
- 742.2 Congenital reduction deformities of brain
- 741.02 Spina bifida with hydrocephalus, dorsal (thoracic) region
- 741.01 Spina bifida with hydrocephalus, cervical region
- 741.03 Spina bifida with hydrocephalus, lumbar region
SNOMED
- Chiari malformation (disorder)
- Chiari malformation type I (disorder)
- Chiari malformation type II
- Chiari malformation type III
- Chiari malformation type IV
CLINICAL PEARLS
- Chiari I malformations are the most common and can be treated conservatively in the absence of symptoms (2)[A].
- Chiari II malformations are treated based on symptoms, typically by surgical decompression (3)[B].
- Chiari III and IV malformations are very rare and they are often found during prenatal testing. Those affected typically do not survive the neonatal period (2)[A].
- Neuropathic pain may be managed with anticonvulsants and antidepressants (2)[A].