Original ArticleChiari Type I Malformation in a Pediatric Population
Introduction
The Chiari type I malformation is characterized by ectopia or herniation of the cerebellar tonsils through the foramen magnum. This malformation typically presents with neurologic symptoms during early adulthood. Although Chiari I is increasingly recognized in children [1], [2], [3], [4], [5], [6], [7], [8], little is known about its natural history. Patients may be asymptomatic or may have a variety of neurologic symptoms, including headache, neck pain, visual disturbances, vertigo, and ataxia [1], [4], [5], [9], [10], [11]. Chiari I may lead to the development of syringomyelia or spinal cord cavitation, which can lead to additional neurologic deficits. Because surgical intervention can improve existing symptoms, as well as prevent further neurologic deterioration from syringomyelia, there may be a benefit to early identification of patients with Chiari I [1], [2], [9], [12], [13], [14].
The cerebellar tonsils rarely descend more than 3 mm below the foramen magnum in normal adults, whereas symptomatic patients with Chiari I usually exhibit at least 5 mm of herniation [15], [16]. Thus, 5 mm has become widely adopted as a cutoff for defining Chiari I, for both clinical and research purposes. This measurement is to some degree arbitrary, and does not include other anatomic factors that may determine if a patient develops symptoms or not. Whether individuals with 2-4 mm of tonsillar ectopia may also exhibit Chiari symptoms that respond to surgical intervention remains a matter of debate [17].
With the increasing availability of diagnostic magnetic resonance imaging, more asymptomatic patients are being identified [4], [5], [18]. Nonetheless, the neurologic prognosis for such patients remains unclear, because long-term natural history studies of Chiari I are lacking. Previous studies of Chiari I consist primarily of neurosurgical case series [1], [2], [3], [5], [9], [11], [19], [20], [21], [22], [23]. With the objective of gaining a better understanding of Chiari I in children, a population-based study was conducted; to our knowledge, this study is the first of its kind.
Section snippets
Methods
A retrospective cohort study was conducted of all children under 20 years of age who were diagnosed with Chiari I within the Kaiser Permanente Medical Care Program (KPMCP) in northern California during 1997 and 1998. An electronic database was searched to identify patients with cerebellar tonsillar ectopia noted on a head or spine magnetic resonance imaging, and medical records and neuroimaging studies were reviewed. This study was approved by institutional review boards at KPMCP and the
Results
During the 2-year study period (January 1997- December 1998), 51 children had a Chiari I identified on a head or spine magnetic resonance imaging study. This diagnosis was present in 1.0% of all 5248 head and spine magnetic resonance imaging scans performed in the study population. The frequency of Chiari I diagnoses in the KPMCP pediatric population was 0.7 per 10,000. Mean age at diagnosis was 11 years (S.D. = 4.8).
Discussion
Despite its recognition more than a century ago [24], Chiari I was difficult to diagnose before the advent of magnetic resonance imaging, and little is known about the epidemiology and natural history of Chiari I, particularly in children. The prevalence of Chiari I remains unknown. In this unique population-based study of Chiari I in children, one third of children diagnosed with Chiari I were asymptomatic at the time of diagnosis, and the majority of symptomatic patients complained of
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