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Posterior fossa dimension and volume estimates in pediatric patients with Chiari I malformations
T Trigylidas1, B Baronia, M Vassilyadi
1Division of Neurosurgery, Children's Hospital of Eastern Ontario, University of Ottawa, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
Insights
Pediatric Chiari I malformation (CMI) patients have smaller posterior fossa volumes (PFV) than controls. Subtle PFV differences in younger CMI patients highlight the need for long-term monitoring.
Area of Science:
- Pediatric Neurosurgery
- Neuroradiology
- Congenital Malformations
Background:
- Chiari I malformation (CMI) is linked to a hypoplastic posterior fossa.
- Traditional CMI diagnosis focuses on cerebellar tonsil descent, but cisterna magna fullness and CSF flow are more indicative of symptoms.
- This study re-examines diagnostic and treatment criteria for pediatric CMI using imaging and clinical data.
Purpose of the Study:
- To calculate posterior fossa dimensions and volume estimates in pediatric patients with Chiari I malformation using MRI.
- To re-evaluate diagnostic and treatment criteria for pediatric CMI by combining neuroradiological and clinical findings.
Main Methods:
- Retrospective chart review of pediatric patients from 1990-2007.
- Measurement of posterior fossa volumes (PFV) and intracranial volumes (ICV) from MRI scans using the Cavalieri method.
- Comparison of PFV/ICV ratios between CMI patients and controls, and between symptomatic and asymptomatic CMI subgroups.
Main Results:
- Sixty-one pediatric CMI patients were identified, with 55% being symptomatic.
- CMI patients exhibited a statistically smaller mean PFV/ICV ratio (0.110) compared to controls (0.127).
- PFV/ICV ratios were similar in asymptomatic and symptomatic children aged 0-9, but differed significantly in those aged 10-18.
Conclusions:
- Pediatric CMI patients have smaller mean PFV than controls, supporting existing pathophysiological theories.
- Subtle morphometric differences in younger patients suggest the need for ongoing monitoring of asymptomatic individuals.
- Symptom development in CMI is complex and not solely determined by cerebellar tonsillar herniation.
Introduction:
Chiari I malformations (CMI) involve pathological hindbrain abnormalities reported to be correlated with a hypoplastic posterior fossa. CMI was traditionally characterized by the downward herniation of the cerebellar tonsils with a descent of 5 mm or more below the foramen magnum. The fullness of the cisterna magna and CSF flow at the level of the cervicomedullary junction have been shown to be more useful in selecting symptomatic patients for surgical decompression. The present study calculates posterior fossa dimension and volume estimates in pediatric patients using magnetic resonance imaging. The combination of neuroradiological and clinical findings is used to re-examine the criteria used for diagnosis and treatment of pediatric CMI patients.
Materials And Methods:
A retrospective chart review was conducted on patients who were admitted to the Division of Neurosurgery of the Children's hospital of Eastern Ontario between 1990 and 2007. Clinical and radiological assessments were performed on all patients. Posterior fossa volumes (PFV) and intracranial volumes (ICV) were measured from sagittal head magnetic resonance imaging scans using the Cavalieri method.
Results:
Sixty-one CMI patients were identified. There were 32 male and 29 female patients with a mean age of 10 years (range: 8 weeks-18 years). Thirty-four (55%) of these patients were symptomatic with scoliosis (38%), suboccipital headaches (29%), and motor/sensory deficits (26%) being the most prominent symptoms. The mean PFV/ICV ratio for all the CMI patients (0.110) was found to be statistically smaller than that of the control patients (0.127, p=0.022). Mean PFV/ICV ratios for asymptomatic and symptomatic CMI patients were found to be similar for children aged 0-9 years (p=0.783) but different for children aged 10-18 years (p=0.018).
Discussion:
Mean PFV values were found to be smaller in pediatric CMI patients than control patients; this complements earlier studies in adults and supports the present theory concerning the pathophysiological mechanism of CMI. Subtle morphometric differences among asymptomatic and symptomatic patients aged 0-9 years stress the importance of monitoring asymptomatic patients for the onset of symptoms in their adult years. Symptom development in CMI is likely multifactorial and is much more extensive than the degree of cerebellar tonsillar herniation.
