Pediatric Chiari malformation: presentation and indications for treatment
With Dr. Francesco T. Mangano
Chapter 1 of 13
Introduction
Introduction and Historical Perspective
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What the experts said
The first described case of Chiari malformation occurred in 1883 with Dr. Cleland, followed by Dr. Chiari reporting on hindbrain herniations and identifying three types, and later Dr. Arnold describing a Chiari 2 case, leading to the term Arnold Chiari malformation.
Chiari 1 through 4 definitions do not represent a continuous spectrum of malformations despite sharing the same name.
Chiari 2 malformations are associated with open neural tube defects and involve caudal displacement of cerebellar vermis, fourth ventricle, and lower brainstem into the foramen magnum.
Chiari 1 malformation is an imaging diagnosis defined as downward displacement of cerebellar tonsils usually to a level of about 5 millimeters below the foramen magnum.
Chiari 1 is generally thought to be congenital, but there is no specific gene; it is probably multigenetic and multifactorial, with familial association reported between 3 and 21% in the literature.
Chiari 1 can be associated with spinal and skull base abnormalities in up to 50% of cases, and has associations with hydrocephalus and tethered cord.
Chiari 0 malformation is described as tonsillar herniation of less than 3 millimeters with a symptomatic syrinx that improves after decompression.
Chiari 1.5 is defined by increased crowding at the foramen magnum with displacement of the brainstem and obex below the foramen magnum level; these patients are more likely to fail and have persistent syrinx after decompression.
The imaging incidence of Chiari 1 in the pediatric population is roughly 3.6%, with approximately 70% of identified patients not symptomatic at presentation.
Syringomyelia occurs in roughly 20 to 75% of Chiari 1 patients on initial imaging, with the majority having cervical spine syrinx and approximately one in five having holocord syrinx at presentation.
Tonsillar displacement prevalence is higher in younger children and decreases as patients reach younger adulthood.
A 2023 review of 700 asymptomatic children without syrinx found roughly 5-6% developed symptoms over time during observation, and about 2-3% developed a syrinx over time.
Published cases of 100 symptomatic patients show improvement over time with observation, with only about 7% worsened with observation only.
There is enough data in the medical literature to warrant watchful observation for patients with non-symptomatic Chiari 1 presenting as children, with natural history more favorable than previously acknowledged.
Most commonly Chiari 1 is an incidental finding; symptomatic patients generally present with headaches and high cervical pain associated with activity or Valsalva maneuvers.
In pediatric populations, typical presentation includes children who must stop playing after short periods due to discomfort, then resume after brief rest.
Other Chiari 1 symptoms include upper motor neuron weakness, incoordination, and brainstem symptoms (swallowing difficulty, central sleep apnea, nystagmus or abnormal eye movements) typically seen more in younger versus older populations.
Syringomyelia is described as enlargement of the central canal, a normal anatomic structure within the spinal cord, generally associated with pain and sensory deficits when symptomatic and can be associated with progressive scoliosis.
General treatment for patients presenting with syringomyelia is surgical decompression at the craniocervical junction, not direct management of the syrinx, though some advocate watchful observation for asymptomatic patients with small syrinx.
MRI of brain and spine is the test of choice to evaluate Chiari 1, providing detailed information about brainstem, cervical spine bones, and brain itself including conditions like hydrocephalus.
Hydrocephalus was identified in Dr. Chiari's first case on postmortem evaluation and is generally reported to be associated with 7-10% of Chiari 1 patients, with literature range between 2 and 18%.
Hydrocephalus has higher association with craniosynostosis and other craniofacial syndromes in Chiari 1 patients.
A six-center study of 549 patients who had decompression for symptomatic Chiari 1 reported 5.1% occurrence of hydrocephalus developing after decompression, typically presenting with headaches, nausea, vomiting, and some with CSF leaks.
Most patients who developed post-decompression hydrocephalus required permanent CSF diversion (ETV or VP shunt) and did quite well ultimately.
The first description of scoliosis association with Chiari 1 was in 1988, with enough evidence in literature to support a relationship between the conditions.
Patients with both Chiari 1 and scoliosis tend to present with atypical features: earlier onset, left apical curve, kyphotic curve, and more commonly with neurologic deficits.
A 2023 study of 825 patients with radiological scoliosis and Chiari with syrinx found roughly 31% had scoliosis, associated with wider and longer syrinxes compared to those without scoliosis.
Regression analysis determined cervical syrinxes and holocord syrinxes were more predictive of scoliosis than other syrinx locations, with average curve of about 30 degrees; tonsillar position was not associated with scoliosis.
Surgical management for Chiari 1 with scoliosis is reserved for patients who progress, fail conservative scoliosis management, or require treatment of syrinx.
Radiographic measurements for craniocervical abnormalities include: posterior base of C2 line (>9mm indicates retroflexed odontoid), McRae's line for basilar invagination (dens should be up to 5mm below line), and clivoaxial angle of 125 degrees.
Complex Chiari 1 patients with BC2 line >9mm and clivoaxial angle <125 degrees progress to fusion roughly 83% of the time, while those with BC2 <9mm and angle >125 degrees progress to fusion only 13% of the time.
There is no known medical treatment for Chiari 1 malformation.
If a patient is identified as not symptomatic after careful history and physical, watchful observation is a good general rule; if a patient presents with appropriate symptoms, surgery is usually recommended.
The goal of surgery for Chiari 1 is identical regardless of technique chosen: restore CSF dynamics, alleviate symptoms, reduce or stabilize syrinx cavity, and halt progression of associated conditions like scoliosis.
Cincinnati Children's Hospital recommends approximately 3x3cm decompression (size-adjusted for pediatric patients), generally removes posterior arch of C1, and thins the dura before using intraoperative ultrasound.
Intraoperative ultrasound evaluates tonsillar anatomy including CSF space (looking for rounded vs pointed tonsils) and dynamic motion; pistonning of tonsils down into C1 region indicates inadequate bony decompression and may require opening and shrinking tonsils.
Important anatomic considerations when opening dura include the tonsils, vertebral arteries coming up through back of cervical spine, and posterior inferior cerebellar arteries that loop around and often obstruct the obex or bottom of fourth ventricle.
Watertight dural closure is one of the most important aspects when opening the dura during Chiari decompression.
CSF leak is the most important complication when opening the dura because it can lead to further symptoms and puts the patient at risk for meningitis or infection if CSF leaks through the skin.
Meta-analysis of 145 articles reports surgical complication rate for Chiari 1 decompression is approximately 3-5%, with worsening symptoms in 5-18% of patients and reoperation rate of roughly 16%.
Common reasons for reoperation include hydrocephalus, craniovertebral junction instability, arachnoid scarring that closes opened areas causing recurring symptoms, and dural graft complications.
The majority of Chiari 1 patients are not symptomatic and are generally watched with repeat images every year to every couple of years while growing to ensure they don't develop symptoms or changes warranting different approach.
For symptomatic patients with appropriate workup (MRI of brain and total spine), surgical decompression is usually successful in relieving general typical symptoms.
Specific and optimum surgical management for Chiari 1 is very controversial and is subject of much ongoing current research, with hope for better recommendations within 5-10 years based on patient presentation.
A small subset of patients present with complex constellation of symptoms (syrinx, scoliosis, hydrocephalus, genetic syndromes, craniocervical abnormalities) that make clinical decision-making very difficult and raise management difficulty to a much different level.
Dr. Francesco Mangano is the Mary Jane and Bob Tritsch Chair and Professor of Neurological Surgery and Pediatrics at Cincinnati Children's Hospital Medical Center, joining in July 2005 after neurosurgical residency at Long Island Jewish Medical Center (2004) and pediatric neurosurgery fellowship at St. Louis Children's Hospital.