The Chiari Malformations were described in the early 1890s by Dr. Hans Chiari, a pathologist in Prague. Since that time our understanding has progressed to find four distinct anomalies of the hindbrain. Chiari III and IV are rare. Here we will discuss the 2 common anomalies: Chiari I and Chiari II. In general, Chiari cases are thought to be congenital, and may be associated with more serious conditions such as brainstem dysfunction or syringomyelia.
Cerebellar tonsillar descent into the foramen magnum.
Signs and Symptoms
Commonly occurs in children (40% less than age 5, 25% age 5-10 and 30% age 10-15).5 Common presenting symptom is pain (60-70%).6,14,15 Usually occipital or upper cervical headache exacerbated by valsalva (straining, cough, sneezing). Usually occipital or upper cervical headache exacerbated by valsalva (straining, cough, sneezing). Other symptoms vary greatly and may include motor (40-74%) and sensory (50%) changes in the extremities, clumsiness (15%), and dysphagia (10%).6,7,14 Syringomyelia may coexist in 60-70% of patients and this results in progressive scoliosis in 30% of these patients.10,14
MRI is gold standard. Evaluate descent of the tonsils to the foramen magnum as measured from a line drawn from the basion to opisthion. Normal tonsillar position was correlated with age.9 Normal when they extend into the foramen magnum up to 6mm in children 0-10 years old, 5mm in 10-29 years old, 4mm in 30 to 79 years old, and 3mm in those patients above 80 years old. Rule out supratentorial mass lesion, hydrocephalus, or history of multiple lumbar punctures, as these conditions may cause tonsillar herniation, which is considered an acquired Chiari.4 Other possible findings: Cervical syrinx (50-70% of patients8), the appearance of the pointed tonsils rather than rounded in normal patients, and evidence of skull base abnormalities such as platybasia, basilar invagination, and ventral compression. Cine-MRI was associated with conflicting results regarding sensitivity and specificity.
Posterior fossa decompression should include a suboccipital craniectomy and C1 laminectomy. Approximately 5-10% of surgeons choose to stop at this point; 45% open the dura and perform a duraplasty, leaving the arachnoid intact; and the other 45% open the arachnoid, lyse arachnoidal adhesions, and often shrink or resect the cerebellar tonsils. Currently, there is no alternative to surgical therapy for Chiari I. Adequate CSF flow from the foramen of Magendie should be visualized at the time of surgery.5 Intracranial pressure monitoring should precede decompression if there is questionable elevation in ICP, as pseudotumor cerebri occasionally accompanies Chiari I. Rule out craniocervical instability with dynamic cervical spine films prior to surgery. Basilar invagination or ventral compression should alert the surgeon to the possibility of chronic craniocervical instability that might need a concomitant craniocervical fusion with or without tansoral odontoid resection. Three indications for surgical treatment: (1) The presence of neurological deficits, especially if progressive. (2) The presence of syringomyelia. (3) Severe intractable symptoms that are debilitating the patient. Make sure that the symptoms are typical for Chiari I (e.g., valsalva-induced occipital headaches and others).
Prognosis and Outcomes
Outcome data on Chiari I are quite difficult to interpret. They are also dependent on age of presentation and surgery. In a series of 71 adult patients, 80-90% of patients presenting with any symptomatology improved initially but patients with foramen magnum syndromes and patients with central cord syndrome were more likely to relapse later (33% and 25% respectively).15 Syringomyelia should resolve after Chiari decompression. Re-exploration of the posterior fossa is preferred before consideration is made to shunt the syrinx directly to the subarachnoid space, pleura, or peritoneum. Symptoms that most consistently improve with surgery are scoliosis of less than 30 degrees, occipital headache, cervical pain, and sleep apnea.11Patients with more brainstem and spinal cord symptoms are less likely to improve than patients with headaches alone.3
- Armonda RA, Citrin CM, Foley KT, Ellenbogen RG. Quantitative cine-mode magnetic resonance imaging of Chiari I malformations: an analysis of cerebrospinal fluid dynamics. Neurosurgery 1994;35:214-223; discussion 223-214.
- Bhadelia RA, Bogdan AR, Wolpert SM, Lev S, Appignani BA, Heilman CB. Cerebrospinal fluid flow waveforms: analysis in patients with Chiari I malformation by means of gated phase-contrast MR imaging velocity measurements. Radiology 1995;196:195-202.
- Dyste GN, Menezes AH, VanGilder JC. Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. J Neurosurg 1989;71:159-168.
- Elster AD, Chen MY. Chiari I malformations: clinical and radiologic reappraisal. Radiology 1992;183:347-353.
- Iskandar B, Oakes W. The Chiari Malformations, in Albright A, Pollack I, Adelson P (eds): Principles and Practice of Pediatric Neurosurgery, ed 1st. New York, NY: Thieme Medical Publishers, 1999.
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- Mampalam TJ, Andrews BT, Gelb D, Ferriero D, Pitts LH. Presentation of type I Chiari malformation after head trauma. Neurosurgery 1988;23:760-762
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- Mikulis DJ, Diaz O, Egglin TK, Sanchez R. Variance of the position of the cerebellar tonsils with age: preliminary report. Radiology 1992;183:725-728.
- Muhonen MG, Menezes AH, Sawin PD, Weinstein SL. Scoliosis in pediatric Chiari malformations without myelodysplasia. J Neurosurg 1992;77:69-77.
- Nagib MG. An approach to symptomatic children (ages 4-14 years) with Chiari type I malformation. Pediatr Neurosurg 1994;21:31-35.
- Naidich TP, McLone DG, Fulling KH. The Chiari II malformation: Part IV. The hindbrain deformity. Neuroradiology 1983;25:179-197.
- Naidich TP, Pudlowski RM, Naidich JB, Gornish M, Rodriguez FJ. Computed tomographic signs of the Chiari II malformation. Part I: Skull and dural partitions. Radiology 1980;134:65-71.
- Nohria V, Oakes WJ. Chiari I malformation: a review of 43 patients. Pediatr Neurosurg 1990;16:222-227.
- Paul KS, Lye RH, Strang FA, Dutton J. Arnold-Chiari malformation. Review of 71 cases. J Neurosurg 1983;58:183-187.
- Samuelsson L, Bergstrom K, Thuomas KA, Hemmingsson A, Wallensten R. MR imaging of syringohydromyelia and Chiari malformations in myelomeningocele patients with scoliosis. AJNR Am J Neuroradiol 1987;8:539-546
- Schmitt HP. "Inverse Chiari type II syndrome" in untreated hydrocephalus and its relationship to typical Arnold-Chiari syndrome. Brain Dev 1981;3:271-275.