The relationship between obesity and symptomatic Chiari I malformation in the pediatric population

Introduction

Chiari I malformation (CM1) is characterized by the caudal displacement of the cerebellar tonsils through the foramen magnum, often referred to as tonsillar herniation or ectopia. Radiographically, CM1 is defined as displacement of the tonsils 5 mm or more below the level of the foramen magnum.[12] Symptoms associated with the ectopic tonsils may result from one or multiple mechanisms such as compression of the medulla and upper cervical spinal cord (cranial nerve dysfunction and myelopathy), disruption of the flow of cerebrospinal fluid (CSF) through the foramen magnum (headache, neck pain, formation of syrinx, and subsequent spinal cord dysfunction symptoms), and compression of cerebellar tissue (ataxia, dysequilibrium, and other cerebellar symptoms).[34] Patients are often clinically asymptomatic from this radiographic finding.

There is evidence suggesting a link between idiopathic intracranial hypertension (IIH), or pseudotumor cerebri/IIH, and CM1.[5678] IIH is a disorder associated with chronically elevated intracranial pressure (ICP) and has its highest incidence in obese women of childbearing age.[910] Banik et al. reported that 24% of patients diagnosed with IIH also showed the presence of CM1 or “cerebellar ectopia,” with cerebellar tonsil displacement >2 mm but <5 mm below the foramen magnum.[11] They posited that the relationship between IIH and formation of CM1 was not purely coincidental.

While IIH once had been considered a rare disorder, it since has become increasingly common. Among overweight or obese women aged 15–44, the incidence of IIH is estimated to be 13–19 cases/100,000.[121314] The increasing incidence of obesity in the United States (U.S.) is hypothesized to be a contributing factor to the increasing incidence of IIH.[1213] The obesity epidemic involves children as well as adults. At present 20–25% of children in the U.S. are either overweight or obese, with an even higher prevalence in certain minority groups.[15] Several lines of evidence link obesity to IIH.[12131617] Two recent studies reported that childhood obesity is strongly associated with an increased risk of IIH in children and adolescents.[1819]

With evidence linking the identification of CM1 in individuals diagnosed with IIH, and evidence that obesity is associated with an increased risk of IIH, the relationship between overweight and obese pediatric patients and CM1 warranted further investigation. The purpose of this study was to examine the impact of obesity on the development of symptoms in CM1 patients and to estimate the magnitude of the association between body mass index (BMI) and the likelihood of young patients presenting with symptomatic CM1.

Methods

Results

The medical records of 167 patients diagnosed with CM1 and seen at Children's Hospital of Pittsburgh between 2007 and 2010 were retrospectively analyzed. No patient had prior surgical treatment for CM1. All patients had complete charts and original magnetic resonance imaging (MRI) scans revealing ≥5 mm of cerebellar tonsillar herniation. The average age at presentation was 14.5 ± 2.97, with a range of 2–20 years. Ninety-four patients (56.2%) were female. The average BMI for all patients was 22.98 ± 6.5, and the mean Chiari size was 12.27 ± 5.91 mm [Table 1]. Twelve patients (7.18%) were 2–9-years-old, 73 (43.71%) were 10–14, and 82 (49.10%) were 15–20. Overall, 42% of the patients were either overweight or obese. According to the BMI-per-age percentiles, two patients (1%) were underweight (BMI < 5^th percentile), 96 patients (57%) were normal weight (BMI between the 5^th and 85^th percentiles), 38 (23%) were overweight (BMI between the 85^th and 95^th percentiles), and 31 (19%) were obese (BMI > 95^th percentile) [Table 2].

Table 1

Patient characteristics

Table 2

Patients divided by BMI category

Many patients were symptomatic at presentation. Sixty-one patients (36.5%) had syringomyelia, 92 (55%) complained of headaches, 11 (6.5%) showed cerebellar symptoms, and 9 (5.3%) presented with brainstem symptoms [Table 3]. Thirty-nine patients (23.3%) had clinically asymptomatic tonsillar descent without other radiographic abnormalities. When stratified by age, important differences between age groups and significant correlations (P < 0.05) between the studied variables were identified [Tables 4 and 5].

Table 3

Signs and symptoms

Table 4

Patient characteristics, signs and symptoms stratified by age

Table 5

Significant correlations stratified by age

Discussion

In this study, we retrospectively reviewed presenting characteristics of pediatric patients with CM1. We found a strong association between a BMI greater than the 85^th percentile and the diagnosis of CM1 in children and adolescents. While several studies have assessed the link between obesity and IIH,[1213] as well as IIH and CM1,[81121] to our knowledge, this is the first study to establish a relationship between childhood obesity and CM1 and to investigate the effects of obesity on CM1-related signs and symptoms.

In recent years, childhood obesity has risen to the forefront of health concerns affecting the U.S. For children and adolescents in the U.S., the prevalence of obesity is approximately 16.9%.[15] The morbidity and mortality associated with obesity is well documented, particularly with regard to cardiovascular disease and diabetes.[1522] With this trend of ever-increasing rates of obesity in recent decades, there has been a concomitant increase in incidence of IIH, indicating that there may be an association between obesity and IIH.[161718] While the pathophysiologic link between obesity and IIH is not fully elucidated, a recent study using three-dimensional volumetric MRI of the brain in adults suggested that impaired CSF homeostasis and venous hemodynamics were present in IIH.[23]

It is reasonable to postulate that elevated ICP, as seen in IIH, contributes to the caudal displacement of the cerebellar tonsils seen in CM1. Banik et al. reported that 16 out of 68 patients (24%) with IIH also had tonsillar ectopia.[11] The majority of these 16 patients were overweight or obese female patients. This is significantly higher than the prevalence of CM1 in the general population, which is estimated to be 0.1–0.5%.[24]

With this study encompassing 167 pediatric patients over a 4-year period, we have attempted to establish a potential link between childhood obesity and diagnosis of CM1 based on existing data on the relationship between obesity, IIH, and CM1. This study demonstrated that pediatric patients presenting with CM1 are more likely to be overweight or obese (42%) when compared to normative BMI values from children for the state of Pennsylvania (29.6%).[25] Our results showed that patients with lower BMI have less CM1-related signs and symptoms than obese patients.

In the study population, BMI-per-age did not have a strict linear correlation with age. Younger patients (2–9 years) were the most obese (BMI: 25.66) and presented a higher incidence of CM1-related symptoms (headache) and signs (syrinx and Chiari size). Although obesity in these patients was significantly correlated with headache, high BMI patients presented less brainstem-related complaints. Patients from the other two stratified groups (10–14 and 15–20 years) were most likely to be overweight (BMI: 21.47 and 23.91, respectively). The analysis of these groups showed that lower BMI patients were less likely to present with headache (68.52% less) and syrinx (58% less) when compared to the most obese group (2–9 years).

Although older patients (15–20 years) presented with the smallest Chiari size, there was a significant correlation between BMI and Chiari size (R²: 0.40, P = 0.03). Patients from this group presented with the highest incidence of cerebellar symptoms (50%)—six times more than patients from the other two groups—and higher incidence of brainstem symptoms (8.55%). However, BMI in this group was inversely correlated with headaches. Further studies are necessary to investigate the mechanisms behind these disparate findings.

The mechanism of the potential link between BMI and CM1 symptoms is not yet understood. It is possible that increased venous pressure in the brain and decreased venous return cause a chronic state of increased ICP, leading to the caudal displacement of the cerebellar tonsils. It is also possible that the skull (and/or posterior fossa) develops to a smaller size due to the mechanical obstruction of increased body mass and neck tissue in obese children.

Conclusion

In summary, the results of this study appear to suggest that the combination of patient age and BMI plays a significant role in the development of CM1 signs and symptoms. Older obese patients presented with significantly larger Chiari malformations, more cerebellar symptoms, and fewer headaches. Obese patients in the younger group presented with more headaches, but lesser cerebellar and brainstem dysfunction. Therefore, both BMI and age should be taken into consideration when evaluating children with CM1. Larger prospective studies would need to be undertaken to explore this association more fully, as well as to address the utility of weight-loss strategies in the prevention or treatment of overweight and obese children with a diagnosis of IIH or CM1.