Evaluation of the evan's and bicaudate index for rural population in central india using computed tomography

Introduction: Evans index (EI) and Bicaudate index (BCI) are practical markers of ventricular volume and are helpful radiological markers in the diagnosis of normal pressure hydrocephalus. Worldwide, variation exists in normative studies for both these indices. Most of the studies conducted for EI and BCI are based on the Western population data. No study has been performed on the rural population of Central India. The purpose of this study is to develop normative data on EI and BCI that can be extrapolated for future reference. Materials and Methods: This was a retrospective study conducted from December 2018 to May 2019 in MGIMS Hospital, Sevagram, Maharashtra, India, which is a rural hospital in Central India. All patients with either a head injury or neurological complaints although with normal computed tomography (CT) brain were included in the study. Patients with diagnosed neurological disorder, clinical features suggesting hydrocephalus, or intracranial pathology on CT brain were excluded from the study. Five hundred and eleven patients were selected for this study, and EI and BCI was calculated for them. Results: The mean value of EI and BCI in our study was 0.2707 and 0.1121, respectively. Both indices showed a statistically significant difference between males and females. The value of both indices increased with age. Conclusion: Although our study is in agreement with the cutoff value of EI to diagnose dilated lateral ventricles as 0.3 for age <70 years, cutoff value of EI for the older population should be reconsidered to 0.34.

Key-words:

Bicaudate index - Evans index - normal pressure hydrocephalus

Introduction

Hydrocephalus is the imbalance in the production and absorption of cerebrospinal fluid (CSF), resulting in the enlargement of the ventricular system.[[1]] For the diagnosis of hydrocephalus, apart from clinical examination, radiological investigation such as computed tomography (CT) and magnetic resonance imaging plays a very important role. The diagnosis of hydrocephalus on imaging is made by assessing the ventricle size.

CT scan is the most widely used and affordable modality for brain imaging. Ventricular size can be studied by linear ratio measurements on CT. Among these, Evan's index (EI) and Bicaudate index (BCI) are the simplest methods of evaluation.

EI is defined as the ratio of the maximum width of the frontal horns of the bilateral lateral ventricles and maximum internal diameter of the skull at the same level.[[2]] BCI is defined as the ratio of the width of bilateral lateral ventricles at the level of the head of the caudate nucleus to distance between inner tables of the skull at the same level[[3]] [[Figure 1]]. Both these indices are practical marker of ventricular volume and have been proposed as helpful biomarkers in the diagnosis of normal pressure hydrocephalus.

Figure 1: Computed tomography brain axial view a = maximum width of the frontal horns of the bilateral lateral ventricles b = maximum internal diameter of the skull at the same level c = Width of bilateral lateral ventricles at the level of the head of the caudate nucleus d = Distance between inner tables of the skull at the same level

Materials and Methods

This was a retrospective study conducted in the Department of Neurosurgery, Mahatma Gandhi Institute of Medical Sciences, Sewagram, Maharashtra, India, from December 2018 to May 2019. Five hundred and eleven patients with clinical symptoms or history suggestive of neurological ailment but with a normal CT brain were analyzed.

Inclusion criteria

All participants who reported to the neurosurgery department with complaints of head injury and neurological disease but with a normal CT brain were included in the study. The youngest child in this series was 6 months, and the oldest patient was 90 years.

Exclusion criteria

1. Participants with intracranial pathology on CT

2. Participants with clinical features suggestive of hydrocephalus

3. Proven case of a neurological disorder.

CT brain of all the patients was performed in Wipro GE multislice CT scanner. Axial sections were obtained at 5-mm slice thickness from the skull base to the vertex along the orbitomeatal plane. Studies were analyzed on ADW workstation. Measurements were taken with inbuilt linear calipers.

Statistical analysis

Statistical analysis was performed using Microsoft Excel 2016. Web-based, open-source application, OpenEpi.com (version 3.01, OpenEpi is a Web-based Epidemiologic and Statistical Calculator for Public Health. It was developed by Kevin M. Sullivan, Andrew Dean and Minn Minn Soe from Atlanta, Georgia, USA) was used for applying unpaired t-test.

Results

Of 511 patients, 345 were male and 166 were female, with a male: female ratio of 2.08:1. Maximum patients were in the age group of 20–40 years [[Figure 2]]. The average age for the study population was 40.86 years. [[Figure 3]] and [[Figure 4]] describe the distribution of EI and BCI in different age groups.

Figure 2: Age-wise distribution of the patients in the case series

Figure 3: Distribution of Evans index in different age groups

Figure 4: Distribution of Bicaudate index in different age groups

[[Table 1]] describes the various parameters used in the study and their final values. [[Table 2]] describes EI and BCI with respect to the age and sex of the patient.

Table 1: Various computed tomography brain parameters

Table 2: Age- and sex-wise distribution of Evans index and Bicaudate index

The value of EI in the study population was 0.2733 ± 0.0301 in males and 0.2655 ± 0.0306 in females. The overall value of EI in the study population was 0.2707 ± 0.0304. The mean value of BCI was 0.116 ± 0.0339 in males and 0.1041 ± 0.0331 in females. The overall value of BCI for the study population was 0.1121 ± 0.0341. For males and females, the value of EI (P = 0.006) and BCI (P = 0.0002) was statistically significant [[Table 3]]. This study shows an increasing trend with age for EI and BCI. There was also statistically significant difference in both EI and BCI with respect to age [[Table 4]]. Patients of age >70 years have the highest values of EI and BCI.

Table 3: Comparison of Evans index and Bicaudate index with respect to sex

Table 4: Comparison of Evans index and Bicaudate index with respect to age

Discussion

EI and BCI are the practical parameters commonly used in the diagnosis of hydrocephalus. Hydrocephalus can be divided as communicating (or nonobstructive) and noncommunicating (or obstructive). The causes of obstructive hydrocephalus are cystic lesions, tumors, or membranous obstruction to CSF outflow.[[4]],[[5]],[[6]] Rarely, it may due to pathology involving the choroid plexus where CSF production takes place leading to excessive CSF production. Obstructive hydrocephalus is the most common type of hydrocephalus in children and young adults.[[7]],[[8]] In some instances, there occurs a complex type of hydrocephalus (e.g., meningitis) where both absorption and flow of CSF are interrupted.[[9]] Several imaging parameters are now under consideration to make a diagnosis of hydrocephalus which includes frontal horn index, occipital horn index, frontooccipital horn ratio (FOHR), frontooccipital horn index ratio, and reduction FOHR. With the advancements in imaging techniques, newer measurement systems such as Huckman number, Bicaudate-Frontal (ventricular) Index, and Schiersmann's Index have also been described.[[10]],[[11]] Many of these tools are time-consuming and partially operator dependent. EI and BCI, being technically less demanding as well as easily reproducible, remain the most commonly used tool for the evaluation of hydrocephalus.

Evans index

EI gives the assessment of the degree of ventricular enlargement. The diagnostic cutoff value is >0.3.[[12]] In the present study, the EI value was 0.2707 ± 0.0304 which was slightly more than other studies with mean EI of 0.25.[[13]],[[14]] This could be attributed to the fact that this study has more percentage of the older population as compared to other studies. In addition, difference could be due to racial and ethnic difference in size of the skull. Takeda et al. reported Evans ratio of 0.271 and 0.262 in the Japanese male and female population, respectively.[[15]] A Turkish study has reported values of 0.27 and 0.28 for males and females, respectively.[[16]]

Hamidu et al. found that mean of EI in males was more than that of the females, but it was not statistically significant.[[13]] In our study, we found the difference of mean EI between males and females as statistically significant [[Table 3]]. This observation is supported by the fact that females >15 years of age have smaller ventricular system as compared to males.[[17]] For EI, values between 0.25 and 0.30 were associated with borderline enlargement, and values above 0.30 were indicative of pathological ventricular dilatation.[[2]] Although our study is in agreement with the cutoff value, but for age >70 years, our study suggests that the upper limit for EI (95-percentile value) in Central India is 0.34.

Bicaudate index

Apart from the evaluation of ventriculomegaly, BCI is used for the diagnosis of Huntington's chorea, cerebral atrophy, and multiple sclerosis.[[3]],[[18]],[[19]]

Cutoff value for BCI for hydrocephalus is 0.25. The value of BCI in our study was 0.112 ± 0.0337, which is similar to the study by Dupont and Rabinstein[[20]] and Park et al.[[21]] The maximum value in our study was 0.22, which was slightly higher than the study conducted by Pelicci et al.[[22]]

In our study, there was a positive correlation between age and BCI. This observation was similar to other studies conducted by Kukuljan et al.,[[23]] Park et al.,[[21]] and Dupont and Rabinstein.[[20]]

Park et al. showed that there is no difference in sex for BCI values.[[21]] However, our study showed a difference in the mean values of both sexes as statistically significant.

Limitations of the study

The results are from a retrospective analysis of patients from a single center. A multicenter analysis would lead to a more robust conclusion of cutoff indices. Patients aged 70 years or above constituted <10% of the study number. Although this number is higher than the number of older patients in other studies, an independent study of a larger series of this age group should be ideally undertaken.

Conclusion

Our study for Central India concludes that EI and BCI have a significant statistical difference between males and females. Both EI and BCI values increase with age. Although the cutoff value of EI for <70 years' population is 0.3, this should be reconsidered for the older population (>70 years).

Conflict of Interest

There are no conflicts of interest.

Financial support and sponsorship

Nil.

• References

• 1 Haslam RH. Hydrocephalous. In: Behrman RE, Kliegman RM, Nelson WE, Vaughan VC, editors. Nelson Text Book of Pediatrics. 14th ed. Philadelphia: W.B. Saunders Co.; 1992. p. 1487.
• 2 Evans WA Jr. An encephalographic ratio for estimating ventricular enlargement and cerebral atrophy. Arch Neurol Psychiatry 1942;47:931-7.
• 3 Barr AN, Heinze WJ, Dobben GD, Valvassori GE, Sugar O. Bicaudate index in computerized tomography of Huntington disease and cerebral atrophy. Neurology 1978;28:1196-200.
• 4 Hodel J, Rahmouni A, Zins M, Vignaud A, Decq P. Magnetic resonance imaging of noncommunicating hydrocephalus. World Neurosurg 2013;79:S21.e9-12.
• 5 Algin O, Turkbey B. Intrathecal gadolinium-enhanced MR cisternography: A comprehensive review. AJNR Am J Neuroradiol 2013;34:14-22.
• 6 Hingwala D, Chatterjee S, Kesavadas C, Thomas B, Kapilamoorthy TR. Applications of 3D CISS sequence for problem solving in neuroimaging. Indian J Radiol Imaging 2011;21:90-7.
• 7 Men S. BOS akım hastalıkları ve hidrosefali. In: Erden I, editor. Nöroradyoloji Manyetik Rezonans Uygulamaları. 1st ed. Ankara: Türk Manyetik Rezonans Derneǧi; 2006. p. 80-95.
• 8 Bonetti MG, Scarabino T, Rosi R, Ceddia A, Salvolini U. Intracranial hypertension. In: Scarabino T, Salvolini U, Jinkins JR, editors. Emergency Neuroradiology. 1st ed. Berlin, Heidelberg: Springer; 2006. p. 195-237.
• 9 Algin O. Role of complex hydrocephalus in unsuccessful endoscopic third ventriculostomy. Childs Nerv Syst 2010;26:3-4.
• 10 Kosourov AK, Gaĭvoronskiĭ IV, Rokhlin GD, Blagova IA, Panfilenko AF.In vivo assessment of various parameters of the brain ventricles with magnetic resonance tomography. Morfologiia 2002;122:71-3.
• 11 Meese W, Kluge W, Grumme T, Hopfenmüller W. CT evaluation of the CSF spaces of healthy persons. Neuroradiology 1980;19:131-6.
• 12 Toma AK, Holl E, Kitchen ND, Watkins LD. Evans' index revisited: The need for an alternative in normal pressure hydrocephalus. Neurosurgery 2011;68:939-44.
• 13 Hamidu AU, Olarinoye-Akorede SA, Ekott DS, Danborno B, Mahmud MR, Balogun MS. Computerized tomographic study of normal Evan's index in adult Nigerians. J Neurosci Rural Pract 2015;6:55-8.
• 14 Reddy VU, Hegde KV, Agrawal A, Pathapati RM, Arumulla M. Normative values for Evan's index on CT scan for apparently healthy individuals. J Anat Soc India 2015;64:137-40.
• 15 Takeda S, Hirashima Y, Ikeda H, Yamamoto H, Sugino M, Endo S. Determination of indices of the corpus callosum associated with normal aging in Japanese individuals. Neuroradiology 2003;45:513-8.
• 16 Sema P, Yasemin OF, Mahmut O, Gül KA, Hilmi YA. Morphometric MRI study of the brain ventricles in healthy Turkish subjects. Int J Morphol 2019;37:554-60.
• 17 Haug G. Age and sex dependence of the size of normal ventricles on computed tomography. Neuroradiology 1977;14:201-4.
• 18 Aylward EH, Schwartz J, Machlin S, Pearlson G. Bicaudate ratio as a measure of caudate volume on MR images. AJNR Am J Neuroradiol 1991;12:1217-22.
• 19 Bermel RA, Bakshi R, Tjoa C, Puli SR, Jacobs L. Bicaudate ratio as a magnetic resonance imaging marker of brain atrophy in multiple sclerosis. Arch Neurol 2002;59:275-80.
• 20 Dupont S, Rabinstein AA. CT evaluation of lateral ventricular dilatation after subarachnoid hemorrhage: Baseline bicaudate index values [correction of balues]. Neurol Res 2013;35:103-6.
• 21 Park CO, Chae KB, Lee SD, Kim Y, Ha YS. The study in frontal ventricular measurement and correlation between cerebroventricular index and cephalic index on normal computed tomography. J Korean Neurosurg Soc 1990;19:608-14.
• 22 Pelicci LJ, Bedrick AD, Cruse RP, Vannucci RC. Frontal ventricular dimensions of the brain in infants and children. Arch Neurol 1979;36:852-3.
• 23 Kukuljan M, Kolic Z, Bonifacic D, Vukas D, Miletic D. Normal bicaudate index by aging. Curr Med Imaging Rev 2009;5:72-4.

Publication History

Received: 15 July 2019

Accepted: 13 November 2019

Article published online:
16 August 2022