ASSESSMENT OF RELATIONSHIP BETWEEN CLINICAL MANIFESTATION OF CHIARI MALFORMATION TYPE I AND CEREBELLAR TONSILS HERNIATION MEASUREMENT WITHIN THE FORAMEN MAGNUM
Authors: Eric Shingiro , Paulin Munyemana , Sylvie Inyange , Emmanuel Rudakemwa , Severien Muneza , David Hakizimana , Emmy Nkusi Agaba 
Published: April 2023

Chiari malformation type I(CMI) is a common condition. It is a subject of controversy from diagnosis to the management (16). Classically the diagnosis is made on clinical basis and radiological measurement of cerebellar tonsils herniation of 5mm or more below the opisthion-basion line in mid-sagittal plane(Mc Rae line.) The aim of our study was to determine the relationship between clinical presentation of CMI and cerebellar tonsil herniation measured in three dimensions, cerebellar tonsils volume and the volume ratio (cerebellar tonsils volume/Foramen magnum volume) within foramen magnum. Can the volume of cerebellar tonsils herniation and the volume ratio(cerebellar tonsils volume/volume foramen magnum) reflect better the severity of patients with CMI? the study is the first in current literature eliciting the relationship between myelopathy severity and headache severity in CMI patients; cerebellar tonsils volume and T/F volume ratio (cerebellar tonsils volume /Foramen magnum volume)

Methods

We conducted an observational cross sectional analytical study. Patients with clinical and radiological confirmation of CMI evaluated on cranial cervical MRI were enrolled. Three dimension morphometric measures of cerebellar tonsils was made, the volume of cerebellar tonsils was calculated using ellipsoid volume formula. The transverse diameter of foramen magnum was measured and the volume of foramen magnum was calculated using sphere formula. We computed various non-parametric statistical tests and hypothesis testing to analyze variation of cerebellar tonsils uniplanar measurements, cerebellar tonsils volume, and T/F volume ratio (Cerebellar tonsils volume/foramen magnum volume), and to analyze correlation between these measurements with the severity of myelopathy using modified Japanese orthopedics association score(mJOA) and headache severity using pain numeric rating scale. We did all the calculations in python 3 using scipy. stats, Wilcoxon, Pearson, seaborn, and matplotlib.pyplot packages and pandas library

Results

Chiari malformation type I was more common in female with 61.5% and male patients with CMI was 38.5%. The majority of patients with CMI were in fourth and fifth decade. Occipital headache was the most presenting symptom followed by limb paraesthesia, vertigo, difficulty walking and bulbar symptoms. Scoliosis associated with CMI was found in 5% while syringomyelia associated with CMI was found in 8%. According to numeric pain scale; patients with CMI mostly presented with severe headache and moderate headache with 58.3% and 41.7 % respectively.

There is difference between right and left sagittal tonsils measurement; the left median sagittal measurement is 7.8 mm while the right median sagittal measurement is 8.8 mm with P-value <0.001

The coronal and sagittal cerebellar tonsils measurements are statistically different. The median difference and interquartile range(IQR) between coronal and sagittal measurements were 0.6(-0.4 1.8) and p-value <0.001 respectively

The finding showed a correlation between myelopathy severity and the volume of herniated cerebellar tonsils as well as correlation between myelopathy severity and T/F volume ratio (Cerebellar tonsils volume/Foramen magnum volume). There was no correlation between headache severity and sagittal measurement as we failed to reject hypothesis p=0.661 Spearman’s correlation coefficient: -0.045 In contrast there was a correlation between headache severity and cerebellar tonsils volume as well as T/F volume ratio with P-value 0.03 in our study.

Conclusion

Two dimensions radiological measurements in assessment of CMI is not reflecting the clinical severity of patients with CMI. Consideration of both clinical presentation and radiological measurement in assessment of severity of CMI is of great importance rather than only considering the cut off 5 mm descent of cerebellar tonsils herniation in midsaggital plan. Cerebellar tonsils volume and T/F volume ratio(cerebellar tonsils volume /foramen magnum volume) are the indicators of severity of myelopathy and headache severity as shown in our study.