Role of Canal Body Ratio in Assessing Cervical Canal Stenosis: A Magnetic Resonance Image Study

Smitha S Naira, Lakshmi A Sb, Gupta A Kc, Ushadevi K Bd

a. Department of Anatomy, Government Medical College, Manjeri, Kerala, India; b. Department of Anatomy, Medical College, Thrissur, Kerala, India; c. Department of Neuro Imaging and Interventional Radiology, National Institute of Mental Health and Neuro Sciences, Bengaluru, Karnataka, India; d. Department of Anatomy, Government Medical College, Thiruvananthapuram, Kerala, India*

Corresponding Author: Dr.Smitha S Nair, Deepaprabha, Pappanamcode PO, Thiruvananthapuram, Kerala – 695018, Phone: +91-9447191026, Email:drsmithasnair@yahoo.com

Abstract

The dimensions of the cervical spinal canal are useful in the diagnosis of diseases like compressive myelopathy and spinal cord injury. So far there are only few studies regarding the dimensions of the cervical spinal canal, that too in western population. Direct determination of standard dimensions is impossible in cadavers by dissection. So this study has been proposed to determine the standard dimensions in normal South Indian population using magnetic resonance imaging (MRI) technology. The MRI study so proposed will provide a standard list of dimensions of the cervical canal in different age groups of both sexes in the living condition. This will be of great help for neurologists and neurosurgeons to compare the standard normal dimensions with those in disease conditions and assist in the management of neurological diseases of cervical spinal cord. (1) To determine the anteroposterior (AP) diameter of spinal canal and body of vertebrae and ratio of the canal to the body at the cervical region. (2) To detect cervical canal stenosis using canal body ratio (CBR) at different cervical vertebral levels in various age groups (20-79 years) of both sexes. The study included 600 patients who had undergone MRI scan of the cervical spine in the Department of Imaging Sciences and Interventional Radiology, Sree Chithra Thirunal Institute of Medical Sciences and Technology, Thiruvananthapuram, Kerala. It included patients of different age groups of both sexes who were classified into 6 groups. T1-weighted axial images were obtained using spin echo sequence. The axial slices were made at the mid vertebral levels from C2 to C7. The AP diameter of the vertebral body and spinal canal with and without soft tissues in axial images at mid cervical vertebral levels from C2 to C7 were noted. Analysis of data was performed by mean standard deviations, independent sample t-test, ANOVA and Chi-square test. The mean AP diameter of the canal, the body of the vertebra, mean CBR among various age groups at different cervical vertebral levels decreases as the age advances. 20.7% of males and 14.2% of females had cervical canal stenosis. The CBR at the mid cervical level can be used as a screening measure to predict the future occurrence of neurological problems resulting from compression.

Key words: Determination of Dimensions of Cervical Spinal Canal, Body of Cervical Vertebra and Canal Body Ratio, MRI Study, Cervical Canal Stenosis

 

Introduction

The spinal canal is the tube, which contains the spinal cord in the vertebral column. The cervical region is the most mobile portion of the spinal cord, and it is here that the earliest disc degenerations are encountered.1 Hence, it is of great interest to neurologists and neurosurgeons.2 Although spinal stenosis has been diagnosed for many years, there is no consensus among neurologists regarding the degree of spinal stenosis.3 This may be due to racial or sexual differences in spinal canal dimensions. Hence, standard dimensions of the spinal canal are needed to determine the presence of spinal stenosis and its severity.3 A knowledge of normal values of spinal canal dimensions in different age groups of both sexes is very essential to compare and diagnose abnormal conditions.4 So far there are only few studies regarding the dimensions of cervical canal, that too in western population.5 Direct determination of standard dimensions is impossible in the cadavers by dissection.6 So, this study has been proposed to determine the standard dimensions in normal south Indian population using magnetic resonance imaging (MRI). The MRI study so proposed will provide a standard list of dimensions of cervical canal in different age groups of both sexes in the living condition.7,8

 

Objectives

  1. To determine the anteroposterior (AP) diameter of spinal canal and body of vertebrae and ratio of canal to body at the cervical region

  2. To detect cervical canal stenosis using canal body ratio (CBR) at different cervical vertebral levels in various age groups (20-79 years) of both sexes.

 

Materials and Methods

The study sample included 600 patients who had undergone MRI scan of cervical spine and found to be normal in the Department of Imaging Sciences and Interventional Radiology, Sree Chithra Thirunal Institute of Medical Sciences and Technology, Thiruvananthapuram, Kerala during the period from April 2009 to October 2010. It included patients of age groups ranging from 20 years to 79 years of both sexes who were classified into 6 age groups (20-29, 30-39, 40-49, 50-59, 60-69, 70-79 years old, 100 patients in each group). Patients included were with a normal cervical spine who presented with loss of memory, weakness, vertigo, headache, impaired hearing, blindness, loss of weight, and convulsions. Patients with signs of raised intracranial tension and with spinal canal pathology were excluded from the study. The subjects under study underwent MRI scan of the cervical spine using a 1.5 Tesla scanner with a surface neck coil. TI-weighted axial images were obtained using a spin echo sequence (Figure 1-3). The axial slices were made at the mid vertebral levels from C2 to C7.10,12,14

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Figure 1. Sagittal image showing the mid cervical vertebral levels from C2 to C7 (Lines – 3, 5, 7, 9, 13, 15)

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Figure 2. Anteroposterior diameter of the canal without soft tissue measured by noting two points. (a) Midpoint on the posterior surface of vertebral body. (b) Junction of laminae of the spinal canal

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Figure 3. Anteroposterior diameter of the vertebral body is measured by noting 2 points. (a) Midpoint of anterior border of vertebral body. (b) Midpoint of posterior border of vertebral body

In each subject, the curve of the cervical spine was assessed for hyperlordosis or kyphosis. Any traumatic or degenerative changes of the spine had been analyzed, and cervical spine constituents were determined.15-19 These components include the AP diameters of the vertebral body and spinal canal in axial images at mid vertebral levels from C2 to C7. From these constituents, CBR at different cervical vertebral levels was calculated. All these measurements were taken three times using a marker caliper, and average value was recorded. Finally, these measurements were correlated with age and sex.

Statistical Analysis

The collected data were entered in MS Excel sheet, analyzed and subjected to statistical analysis using Statistical Package for the Social Sciences. Analysis of the data was performed using methods such as mean, standard deviation, independent sample t-test, ANOVA, and Chi-square test

 

Results and Analysis

The AP diameter of the spinal canal was maximum at C2 level. Thereafter the diameter gradually decreased in C3 and C4 levels. Then a sudden increase in the diameter was noted at C5 and C6 levels. Then the diameter decreased and was minimum at C7 level. In males AP diameter of the canal was 1-1.5 mm more than that of females (Table 1).

Table 1. Comparison of mean AP diameter of the spinal canal of both sexes at different cervical vertebral levels

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The mean AP diameter of the spinal canal among various age groups at different cervical vertebral levels decreases as the age advances (Table 2).

Table 2. Comparison of mean AP diameter of spinal canal among various age groups at different cervical vertebral levels

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The mean AP diameter of the body of cervical vertebrae in males is about 1.2-1.5 mm more than that of females (Table 3).

Table 3. Comparison of mean AP diameter of body of vertebrae of both sexes at different cervical vertebral levels

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The mean AP diameter of the body of vertebrae among various age groups at different cervical vertebral levels decreases as the age advances (Table 4).

Table 4. Comparison of mean AP diameter of body of vertebrae among various age groups at different cervical vertebral levels

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Independent sample t-test is applied. P>0.05. So, the difference in mean CBR between males and females is not statistically significant at all cervical vertebral levels (Table 5).

Table 5. Comparison of mean CBR of both sexes at different cervical vertebral levels

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The mean CBR among various age groups at different cervical vertebral levels decreases as the age advances (Table 6).

Table 6. Comparison of mean CBR among various age groups at different cervical vertebral levels

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Chi-square test is applied to note the distribution of CBR values among various age groups at C4, C5, C6 vertebral level. P<0.05. So, the distribution of these values at this levels are statistically significant (Table 7-9).

Table 7. Distribution of CBR values at C4 vertebral levels in males and females of various age groups

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Table 8. Distribution of CBR values at C5 vertebral levels in males and females of various age groups

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Table 9. Distribution of CBR values at C6 vertebral levels in males and females of various age groups

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Discussion

The main objective of this study is to determine the normal dimensions of the cervical spinal canal and body of a cervical vertebra in the South Indian population. With this information, the study gives guidelines to physicians and surgeons to make decisions regarding diagnosis and treatment of cervical spinal diseases in South Indian population.

Dimensions of Cervical Spinal Canal

In our study, the AP diameter of the canal was maximum at C2 level. Thereafter, the diameter gradually decreased in C3 and C4 levels. Then a sudden increase in the diameter was noted at C5 and C6 levels. Below this level the diameter decreased and was minimum at C7 level. This is to accommodate the cervical enlargement of the spinal cord.

The difference in mean AP diameters of the canal between males and females among various age groups was found to be statistically significant. In males, the diameters were 1-1.5 mm more than that of females. The results of our study well correlated with the radiologic study of Burrows,3 Nagashima16 and P Matsuura et al.13 In the study by Hashimoto and Tak9 and Hukuda and Kojima10 there was no sexual difference in AP diameter of the canal.

 

Dimensions of Body of Cervical Vertebrae

The difference in mean AP diameters of the vertebrae between males and females in various age groups was statistically significant at all cervical vertebral levels. The mean AP diameter of the vertebrae in males was about 1.2-1.5 mm more than that of females. The mean AP diameter was maximum for C2 vertebrae and minimum for C7 vertebrae. Our study coincides with the study of Lee et al11 who noted larger diameters in men. The mean AP diameter of the vertebrae among various age groups at different cervical vertebral levels decreases as the age advances.

Table 10 compares the different western studies20-24 with our study. Almost similar results were observed regarding the dimensions. However, our observations showed that the AP diameter of cervical spinal canal and body of vertebrae are 1-2 mm lower in south Indian population than the western population. This can be accounted to differences in build between Indian and western population.

Table 10. Normal values of mean anteroposterior diameter of cervical spinal canal and vertebral body in various studies

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Relationship between Mid-cervical CBR (Pavlov ratio) and Cervical Canal Stenosis

In our study, the difference in mean CBR between males and females was not statistically significant. Our study correlates well with the radiologic study by Torg et al.20 However it differs from the study of Hukuda and Kojima10 and Lee et al11 who noted a significantly small CBR in men. The difference in mean CBR among various age groups was statistically significant.

In our study group, the CBR values at C4, C5 and C6 (mid-cervical) levels showed the following values.

Above 60 years age group: About 65% males and 52% females had CBR <0.8, showing cervical canal stenosis. In 25% males and 16% females, CBR lies between 0.8 and 0.85, which was prone to develop stenosis.

Below 60 year age group: In 20-29 year age group, both in males and females 80% showed CBR >1 (safe cervical spinal canal). In 20%, CBR between 0.8 and 0.85, which was prone to develop stenosis.

In 30-59 year age group: 3% males and 9% females showed CBR <0.8 showing cervical canal stenosis,65% males and 66% females showed CBR between 0.8 and 0.85, 32% males and 25% females showed CBR>1.

Irrespective of age groups in our study group, 20.7% of males and 14.2% of females had cervical canal stenosis (18% of total group). There is more chance of cervical canal stenosis above the age of 60 years. The study shows the increasing prevalence of cervical canal stenosis in the younger age group from 30 years onwards. This may be due to degenerative changes occurring to the tissues around the cord in the spinal canal. In South Indian population, about 18% of total population is found to have stenotic changes. They may develop neurological problems in their future life. Further studies are required in this field to find out the cause for degenerative changes occurring at 30 years. However by advising precautionary measures such as change in diet, daily exercises, medicines, physiotherapy etc., future changes in the canal can be prevented and serious neurological complications can be avoided in the population.

Hence, the CBR at the mid cervical level can be used as a screening measurement to predict the future occurrence of neurological problems resulting from compression of the cervical spinal cord.

 

Conclusion

In males, the AP diameter of the cervical spinal canal was 1-1.5 mm more than that of females. The mean AP diameter of the canal at different cervical vertebral levels decreases as the age advances. The mean AP diameter of the body of vertebrae in males was about 1.2-1.5 mm more than that of females. The mean AP diameter of the body of vertebrae among various age groups at different cervical vertebral levels decreases as the age advances. From the study, a list of normal spinal canal dimensions and CBR in different age groups of both sexes were obtained. In short, the narrow spinal canal, large vertebral body and male gender can be taken as the risk factors for cervical myelopathy. So, this study has highlighted the importance of screening measurement such as CBR in determining the cervical canal stenosis. By advising suitable precautionary measures, future changes in the canal can be prevented and serious neurological complications can be avoided in our population. This study gives scope for further clinical research to establish causes for early degenerative changes in the canal.

 

End Note

Author Information

  1. Dr. Smitha S Nair, Assistant Professor, Department of Anatomy, Government Medical College, Manjeri, Kerala, India; Deepaprabha, Pappanamcode PO, Thiruvananthapuram, Kerala, India. Phone:+91-9447191026, Email: drsmithasnair@yahoo.com

  2. Dr. Lakshmi A S, Additional Professor, Department of Anatomy, Medical College, Thrissur, Kerala, India; 350, 5th Cross, IC Main RR Layout, Bengaluru – 560 056, Karnataka, India. Phone: +91-9995369265, Email: lakshmipadmanabhanblr@gmail.com

  3. Dr. Gupta A K, Professor and Head, Department of Neuro Imaging and Interventional Radiology, National Institute of Mental Health and Neuro Science, Bengaluru – 560 029, Karnataka, India. Mobile: +91-9483529650, +91-8089738631, Email: gupta209@gmail.com

  4. Dr. Ushadevi K B, Additional Professor, Department of Anatomy, Government Medical College, Thiruvananthapuram, Kerala, India; Krishna, Kulangarakonam, Naruvamoodu PO, Nemom, Thiruvananthapuram, Kerala, India. Phone: +91-9947991312, Email: ushakbdevi1@gmail.com

 

Conflict of Interest

None declared.

 

List of Abbreviations

  • Canal AP: Anteroposterior diameter of the canal

  • VAP: Anteroposterior diameter of the vertebral body

  • CBR: Canal body ratio

  • C2: At second cervical vertebral level

  • C3: At third cervical vertebral level

  • C4: At fourth cervical vertebral level

  • C5: At fifth cervical vertebral level

  • C6: At sixth cervical vertebral level

  • C7: At seventh cervical vertebral level

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