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Surgical Decision-Making and Treatment Options for Chiari Malformations in Children
Introduction
The Chiari malformations encompass a range of hindbrain anomalies. Classically, four subtypes were described ( Table 72.1 ). Chiari 1 malformations are characterized by cerebellar tonsillar herniation through the foramen magnum, and may be congenital or acquired. Patients with Chiari I malformations may develop hydrocephalus, syringomyelia, and/or scoliosis. , Chiari 2 malformations feature herniation of the cerebellar vermis, medulla, and fourth ventricle through the foramen magnum, and are associated with a variety of other abnormalities throughout the central nervous system (CNS). Chiari 3 malformations are rare, and represent the most severe form of hindbrain herniation, characterized by a high cervical or suboccipital encephalocele containing cerebellar and/or brainstem tissue. Chiari 4 malformations are not associated with hindbrain herniation; instead, patients demonstrate cerebellar hypoplasia or aplasia.
Table 72.1
Chiari Malformation Subtypes
| Chiari | Features |
|---|---|
| Type 0 | Syringomyelia in absence of tonsillar herniation |
| Type 1 | Tonsillar herniation through the foramen magnum; may be associated with hydrocephalus, syringomyelia, and/or scoliosis |
| Type 1.5 | Cerebellar tonsillar ectopia without neural tube defects, but with caudal descent of the brainstem and/or fourth ventricle |
| Type 2 | Herniation of cerebellar vermis, brainstem, and/or fourth ventricle through the foramen magnum; associated with neural tube defects |
| Type 3 | High cervical or suboccipital encephalocele containing cerebellar and/or brainstem tissue |
| Type 4 | Cerebellar hypoplasia or aplasia |
More recently, additional subtypes have been described. Chiari 0 malformations occur in patients without tonsillar herniation, but with syringohydromyelia that improves following posterior fossa decompression (PFD). , Patients with Chiari 1.5 malformations have cerebellar tonsillar ectopia without neural tube defects (similar to patients with Chiari I malformations), but also demonstrate caudal descent of the brainstem and/or fourth ventricle (similar to patients with Chiari 2 malformations).
Surgery is the treatment of choice for patients with symptomatic Chiari malformations. Here, we will discuss surgical decision-making and treatment options for congenital Chiari 1 malformations in children. In general, this discussion can be extrapolated to patients with Chiari 0 and Chiari 1.5 malformations, as well. Patients with acquired Chiari malformations are not included here, as these are typically managed by treating the underlying pathology. Additionally, Chiari 2, Chiari 3, and Chiari 4 malformations represent more complex situations and should be considered separately.
Surgical decision-making in children with Chiari 1 malformations centers on two primary issues: (1) indications for surgical intervention, and (2) surgical treatment options. When hydrocephalus is present, appropriate cerebrospinal fluid (CSF) diversion should be undertaken via shunt placement or endoscopic third ventriculostomy (ETV) prior to decompression of the posterior fossa. If a shunt has already been placed, shunt malfunction should be ruled out. In the absence of hydrocephalus, however, surgical decision-making becomes more controversial.
Indications for Surgery
Asymptomatic Patients
The widespread availability of magnetic resonance imaging (MRI) has resulted in an increased number of asymptomatic patients being diagnosed with incidental Chiari 1 malformations. Several studies have examined thousands of pediatric patients undergoing brain or cervical spine MRI scans, and have identified Chiari I malformations in 0.4% to 2.4% of asymptomatic patients. Survey data collected from the American Association of Neurological Surgeons/Congress of Neurological Surgeons Section on Pediatric Neurosurgery in 1998 demonstrated that 83% of pediatric neurosurgeons would not operate on an asymptomatic child with a Chiari 1 malformation, whether or not syringomyelia was present. However, 61% of respondents favored surgical intervention in the setting of asymptomatic syrinx progression. In contrast, a survey of members of the American Society of Pediatric Neurosurgery (ASPN) performed at their 2006 annual meeting found that 85% of respondents would offer a suboccipital decompression to an asymptomatic patient with a large syrinx, indicating that syringomyelia has become a more common indication for surgical intervention among American pediatric neurosurgeons.
International survey data have also demonstrated the importance of syringomyelia in surgical decision-making when faced with an asymptomatic patient. In the early 2000s, a survey of International Society of Pediatric Neurosurgery (ISPN) members revealed an overwhelming consensus amongst 92% of pediatric neurosurgeons, who recommended nonoperative management of asymptomatic patients with Chiari 1 malformations without syringomyelia. Patients presenting with a thoracic syrinx were more likely to undergo decompression, particularly when the syrinx was large (28% of respondents recommended intervention for a 2 mm syrinx, compared to 75% of respondents for an 8 mm syrinx). ISPN members were again surveyed in 2016 with similar results; only 7% of respondents recommended surgery for asymptomatic patients without syringomyelia, compared to 32% of respondents in the setting of a 2 mm syrinx, and 78% in the setting of an 8 mm syrinx.
Several observational studies have shed light on the natural history of Chiari 1 malformations in asymptomatic patients who are managed nonoperatively. , Tonsillar descent and syringomyelia are radiologically dynamic entities, and follow-up imaging may even demonstrate resolution of the Chiari 1 malformation in some patients, while others experience worsening with time. The clinical significance of radiological changes such as these are not well understood, and some authors have discouraged the use of routine surveillance MRI scans. Nevertheless, regular clinical follow-up should be considered. Although the majority of asymptomatic patients have a benign course, approximately 5% to 10% of patients who are initially managed nonoperatively ultimately become symptomatic and require surgical intervention. , , ,
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