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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 71  |  Issue : 4  |  Page : 272-278

Stereological and comparative evaluation of the carpal tunnel in patients with carpal tunnel syndrome using magnetic resonance images


1 Vocational School of Health Services, Ondokuz Mayis University, Samsun, Turkey
2 Department of Anatomy, Faculty of Medicine, Ondokuz Mayis University, Samsun, Turkey
3 Department of Neurology, Faculty of Medicine, Ondokuz Mayis University, Samsun, Turkey
4 Department of Radiology, Faculty of Medicine, Ondokuz Mayis University, Samsun, Turkey

Date of Submission10-Apr-2021
Date of Decision26-Jul-2022
Date of Acceptance13-Sep-2022
Date of Web Publication01-Dec-2022

Correspondence Address:
Prof. Mehmet Emirzeoglu
Department of Anatomy, Faculty of Medicine, Ondokuz Mayis University, Samsun
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jasi.jasi_71_21

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  Abstract 


Introduction: In this study, the relation between carpal tunnel syndrome (CTS) severity and the carpal tunnel volume (CTV), volume and the volume fraction of the carpal tunnel contents on subjects with CTS and healthy individuals were examined. Material and Methods: 30 female patients diagnosed with CTS clinically and electrophysiologically and 16 healthy female patients were included in this study. In patient group, 50 and in control group 30 hand wrists were examined. CTS severity was ranked electrophysiologically. T1-weighted axial magnetic resonance images (MRIs) were examined by the Cavalieri principle. Results: CTV in the patient group (4.26 ± 0.57 cm3) was found to be lower than that of the control group (4.66 ± 0.73 cm3), while the volume (0.41 ± 0.07 cm3) of the median nerve (Vnm) in the patient group was found to be higher than the control group (P < 0.05). Besides, the volume and volume fraction of the median nerve increase when the CTS severity increases (r = 0.610; r = 0.778). Discussion and Conclusion: Our study has shown that stereological studies with MRI are successful in determining the CTV in differentiating patients and healthy people. In addition, the volume and volume fraction of the median nerve were found to be quite effective in differentiating the severity of CTS. It is anatomically confirmed that when the severity of CTS increases, the space volume fraction of the carpal tunnel decreases.

Keywords: Carpal tunnel syndrome severity, carpal tunnel syndrome, magnetic resonance imaging, median nerve, volume fraction


How to cite this article:
K. Güven GA, Emirzeoglu M, Terzi M, Selçuk MB, Sahin B. Stereological and comparative evaluation of the carpal tunnel in patients with carpal tunnel syndrome using magnetic resonance images. J Anat Soc India 2022;71:272-8

How to cite this URL:
K. Güven GA, Emirzeoglu M, Terzi M, Selçuk MB, Sahin B. Stereological and comparative evaluation of the carpal tunnel in patients with carpal tunnel syndrome using magnetic resonance images. J Anat Soc India [serial online] 2022 [cited 2023 Feb 4];71:272-8. Available from: https://www.jasi.org.in/text.asp?2022/71/4/272/362554




  Introduction Top


Carpal tunnel syndrome (CTS) is a common neuropathy that occurs by compression of the median nerve under the flexor retinaculum based on various pathological reasons. CTS mainly affects the 4%–5% of the age group of 40–60 years.[1] The carpal tunnel composition and decrease of the space in the carpal tunnel, triggering situations that increase the pressure coming from inside and outside of tunnel, can cause CTS easily. Although it is well documented that CTS's cause is due to the median nerve compression, the biological mechanism underlying the compression remained unknown.[2],[3],[4]

The stereological studies in accordance with Cavalieri principle help to estimate the volume of the biological structures. The content volume, volume fraction of that contents, or their fraction in proportion to the included total volume is evaluated in a scientific discipline with this approach. The unbiased and reliable results support the diagnosis and effective treatment of the diseases.[5],[6]

The consensus about the criteria of CTS diagnosis in clinical fields is essential to provide effective treatment. The use of stereological techniques can also play an active role in explaining the morphology of the carpal tunnel and cases that are difficult to diagnose. Therefore, stereological studies done by cross-sectional imaging methods such as magnetic resonance (MR) and computed tomography are required substantially. In this study, we aimed to evaluate the effectiveness of stereological techniques in the diagnosis and severity of CTS.


  Material and Methods Top


This study was approved by the Clinical Researches Local Ethics Committee. Volunteers were informed about the content, aim, and application of the study and their approvals were obtained. A questionnaire was conducted for the general health status of patients. Those who underwent trauma, steroid injection, and surgical operations on the wrist arthroscopy area were not included in the study. Patients who could not be evaluated due to moving their hands during MR were also excluded from the study. Carpal tunnel volume (CTV), the size differences of the tendons, and the median nerve between the patient and healthy groups with their fraction within the tunnel and their relations with CTS degree were examined in this study through the MR images (MRIs).

Thirty female patients with CTS participated in the study by performing physical examination and electrophysiological and clinical tests. The control group included 16 healthy female volunteers. In the patient group, 50 MRIs were obtained from bilateral wrists. In the control group, 16 right and 14 left MRIs of the wrist were obtained.

MRI imaging was performed using a 1.5-T scanner (Gyroscan Intera, Philips Healthcare, Best, the Netherlands). T1 weighted and three dimensional images were obtained. Axial T1-weighted turbo spin echo sequence: field of view [FOV]: 200 mm × 244 mm, (repetition time [TR]/echo time [TE]: 570/24 ms; 90° flip angle; 100% phase resolution; slice thickness: 3 mm; number of excitations [NEX]: 2; intersection gap: 0.3mm) and monitoring time was 10 min 18 s. The imaging was performed in the neutral position starting with radiocarpal articulation in the axial plane up to the proximal degree of metacarpal bones using by wrist coil. The imaging was performed in the neutral position starting with radiocarpal articulation in the axial plane up to the proximal degree of metacarpal bones using by wrist coil.

All patients were assessed by a neurologist with more than 10 years of experience. The cases with CTS were classified according to clinical assessment and the EMG (Electromyography) symptoms as mild CTS, moderate CTS, and severe CTS.[7],[8] Volume measurements were conducted according to the Cavalieri principle to measure the volume and volume fraction of the contents of the tunnel volume (Vt/CTV, Vmn/CTV) such as carpal tunnel, flexor tendons, and median nerve.[9] The volume within a 3-cm segment of carpal tunnel was measured on 6–9 MR sections. Carpal tunnel was visible on 6–9 MR sections.

T1-weighted axial MRIs starting from distal of radius were taken in a way to include carpal tunnel completely which is located in proximal of metacarpals. Acquired MRIs were saved in DICOM format. In each section, the borders of the carpal tunnel, median nerve, and flexor tendon were analyzed by the ImageJ software, which is distributed freely by the National Institutes of Health of the USA. The borders of the carpal tunnel and median nerve were delineated using the polygon selection tool in the ImageJ. The sectional surface is the structures that were obtained automatically by the software [Figure 1]a, [Figure 1]b, [Figure 1]c. To calculate the projection area of the tendons, the image threshold of the sections was done and the sectional surface areas were measured [Figure 1]d. All measurements were repeated ten times in each patient before starting the study. The two persons who made the measurements were blinded to the clinical evaluation and classification of electromyography. The obtained sectional cut surface areas were multiplied by the section thickness and the volumes of the total carpal tunnel, tendons, and median nerve were estimated using the Cavalieri principle. The following terms were used to determine the volume fraction of the median nerve and tendons to the CTV.
Figure 1: Measurement of volume and carpal tunnel contents using the ImageJ software. (a) Delineation of the boundaries of the carpal tunnel, (b) Measuring of the carpal tunnel surface area, (c) Measuring of the median nerve area, (d) Delineation of the boundaries of the flexor tendons in the carpal tunnel by threshold tool

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The volume fraction of the median nerve = ([Vnm/CTV] ×100).

The volume fraction of tendon = ([Vt/CTV] ×100).

The free space volume fraction within the total CTV was estimated as follows:

The space volume fraction of the carpal tunnel = 100 − ([Vnm/CTV) ×100] + ([Vt/CTV] ×100).

All the data were analyzed using the Statistical Package for the Social Sciences (SPSS v. 15). The carpal tunnel and canal content volume of the participants with mean values of volume fraction of flexor tendon and median nerve to the canal were calculated. The estimated data of the carpal tunnel, flexor tendons, and median nerve were controlled for the statistical distribution. Normal parametric statistics were used due to the normal distribution of the data. Student's t-test was used to compare results between the patient and control groups. One-way ANOVA and Tukey test were used for the evaluation of the severity types of CTS. The correlation was evaluated by Pearson and Spearmen coefficient of correlation according to the given convenience. Statistical significance level was accepted as P ≤ 0.05.


  Results Top


The mean age of the patient group was 51.07 ± 11.90 years (minimum 25, maximum 75) and the mean age of the control group was 48.56 ± 10.09 years (minimum 35, maximum 65). There was no difference in terms of age between the patient and control groups (P > 0.05). Fifty MRIs of wrists in the patient group and 30 MRIs of wrists in the control group were evaluated without regarding the left or right hand. The mean of total CTV in the patient group was found lower than the control group (P < 0.05). There was no difference in the mean of total tendon volumes between the groups (P > 0.05). The mean of median nerve volume in the patient group was higher than the control group [P < 0.05, [Table 1]]. The mean volume fraction of tendon volume and median nerve volume in the patient group was higher than the control group (P < 0.05). The mean volume fraction of space of the carpal tunnel in the patient group was lower than the control group [P < 0.05, [Table 2]].
Table 1: The mean volumes of the carpal tunnel and tendons and median nerve and comparisons of volume values in patients with carpal tunnel syndrome (n=50) and control group (n=30)

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Table 2: Statistical comparison of volume fraction measured in patients with carpal tunnel syndrome (n=50) and control group (n=30)

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The relation between carpal tunnel and canal content volume and volume fraction was evaluated according to the Spearman correlation coefficient calculation. There was a high positive correlation between CTV and tendon volume (r = 0.658, P = 0.000), median nerve volume and median nerve volume fraction (r = 0.778, P = 0.000). A remarkable negative correlation was observed between the space of the carpal tunnel and the tendon volume fraction (r = −0.963, P = 0.000). There was a low negative correlation between the space of the carpal tunnel and the median nerve (r = -0.375; P = 0.000). A remarkable negative correlation was found between the space of the carpal tunnel and the median nerve volume fraction (r = -0.612, P = 0.000). In the patient group, 21 hand wrists (42%) with mild CTS, 24 hand wrists (48%) with moderate CTS, and 5 hand wrists (10%) with severe CTS were detected.

While there was no significant difference in tendon volumes (P > 0.05), significant differences were observed between CTV, median volume, median nerve volume fraction, and tendon volume fraction for CTS severity (P < 0.05). A significant difference was found between non-CTS and mild CTS for the mean CTV [P < 0.05; [Figure 2]]. The median nerve volumes of individuals without CTS were significantly different from other CTS severities and median nerve volume increased in concordance with CTS severity [P < 0.05; [Figure 3]]. Furthermore, a significant difference (P = 0.007) was observed between mild CTS and severe CTS [P < 0.05; [Figure 3]].
Figure 2: Mean CTV values regarding the severity of the CTS. CTV: Carpal tunnel volume, CTS: Carpal tunnel syndrome

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Figure 3: Mean median nerve volume values regarding the severity of the CTS. CTS: Carpal tunnel syndrome

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When we compared the volume fraction according to CTS severities, an increase was observed in the volume fraction of tendons and median nerve in concordance with the degree of severity among the CTS severities. Controversially, the space volume fraction of carpal tunnel decreased in concordance with CTS severity degree [P < 0.05; [Figure 4], [Figure 5], [Figure 6]].
Figure 4: Mean space of the CTV fraction regarding the severity of the CTS. CTV: Carpal tunnel volume, CTS: Carpal tunnel syndrome

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Figure 5: Mean volumes regarding the severity of the CTS. CTS: Carpal tunnel syndrome

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Figure 6: Mean volume fraction among CTS severities. CTS: Carpal tunnel syndrome

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Moderate correlation between CTS severity and median nerve volume (r = 0.610, P = 0.000), high correlation between CTS severity and median nerve volume fraction (r = 0.778, P = 0.000), week positive correlation between CTS severity and tendon volume fraction (r = 0.446, P = 0.000), and moderate correlation between CTS severity and space of canal volume fraction (r = −0.616, P = 0.000) were observed.


  Discussion Top


In this study, the carpal tunnel volume and its structures (nervus medianus and tendons) were measured to determine the severity of CTS. Carpal tunnel contents and the volume ratio values of these contents to the tunnel were obtained by stereological method. In this way, the 3-dimensional evaluation of the Carpal tunnel was made. Among these values, the most spectacular one is that the free space volume fraction of carpal tunnel decreased while the difference between volume and volume fractions of median nerve increased as CTS severity increased. Accordingly, this is a compatible finding with the studies[10],[11] specifying an increase in carpal tunnel contents as a common characteristic of CTS. Besides, it is known that the volumes of carpal tunnel and contents within the tunnel affect the inner tunnel pressure.[12],[13] In literature, carpal tunnel area studies have been done, including predominantly nerve conduction studies and secondarily median nerve area.[14],[15],[16],[17],[18] In addition, studies indicating the nervus medianus volume and CTV in patients with CTS are remarkable.[14],[19],[20] Moreover, the fractions of the tunnel contents were researched in different studies.[4],[21] There are some studies analyzing CTS severity with Doppler ultrasonography (USG) or MRI in the literature.[7],[17],[22],[23] However, studies that find a mean volume value of median nerve depending on CTS severity or specify free space volume fraction of carpal tunnel quantitatively are not encountered. CTS severity may be determined by stereological methods without the need for a radiology specialist. The other finding of the study was that the volume of the carpal tunnel is found to be successful in differentiating sick and healthy people while unsuccessful in determining the severity of the CTS [Figure 2]. Moreover, this finding is quite compatible with the studies that indicate potential tendency to have smaller cross-sectional areas of carpal tunnel and increase in the fraction of the tendon to the tunnel in CTS etiology.[24],[25],[26] Since the CTV of patients with CTS is less, it is very important to reduce the treatment cost of CTS as a result of early diagnosis in people who are genetically susceptible to CTS.

In our study, it was determined that the median nerve volume was higher and the CTV was lower in the patient group compared to the control group. While the volume value of the carpal tunnel achieved by Pacek et al.[27] with the study on cadavers is quite lower than our study, the volume of the carpal tunnel and the contents achieved by Richman and Cobb again with the study on cadavers is observed as close to our data.[4],[28] Ablove et al. calculated the volume of the carpal tunnel as 4600 mm3.[29] It is also noteworthy that the CTV values obtained by Pierre-Jerome et al. were quite high compared to our values and other measured volume values.[30],[31] We thought that these differences are because of heterogeneous studies, studies done by different operators, patient characteristics,[32] studies on cadavers, and different study groups. In our study, it was found that the volume fraction of tendons and median nerves increased and the carpal tunnel space decreased because of the small volume of the carpal tunnel in patients with CTS according to the volume fractions [Table 2] and [Table 3]. Bower et al. stated that the volume of the carpal tunnel on neutral position is 3737 mm3 and the fraction of the canal contents to the carpal tunnel (CTCv/CTV) is 40%–43% by analyzing the MRIs of the right (the dominant one) wrist positions (flexion, extension, and neutral) of 4 healthy women and 4 healthy men.[3] We think that the volume of the right wrist carpal tunnel in the neutral position is smaller than our values because of the fact that the number of our cases is higher. While Bower et al. achieved the fraction of the carpal tunnel contents, we achieved the fraction of the canal free space. Oge et al. found that the fractions of the content area (tendon + median nerve/the area of the carpal tunnel) increase in patients with carpal tunnel, but the volume of the carpal tunnel is not different in both patients and healthy people.[21]
Table 3: The relation between carpal tunnel and canal content volume and volume fraction in patients with CTS (n=50)

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It may be considered that idiopathic CTS might depend on the incompatibility of the median nerve and the volume of the carpal tunnel since the increase of internal pressure in carpal tunnel results in edema in the nerve and circulatory disorder.[10] In addition, Uchiyama et al. stated that the increasing area of the carpal tunnel may depend on the flexor tendons and the median nerve.[33]

If we look at the volume and the volume fraction according to the CTS severity, it is observed that the estimation of the volume of the carpal tunnel was successful at distinguishing patients and healthy people but unsuccessful at distinguishing CTS severity [Figure 2]. Furthermore, the volume and the volume fraction of the median nerve were quite effective in distinguishing CTS severity [Figure 5] and [Table 3]. While the severity of CTS increased, the difference between volume fractions of the tendons increased in accordance with healthy people [Figure 5]. The volume fractions of the tendons were important in order to determine the severity of the CTS [Figure 6] and [Table 3]. When the CTS severity increased, the free space of the carpal tunnel decreased [Figure 6] and [Table 3]. No volumetric study about CTS severity is encountered in the literature. Moreover, it is observed that all the other studies about the volume and the volume fractions have been done on cadavers or only healthy people until today. Furthermore, in the studies on cadavers, there are some striking elements such as a small number of cadavers, not specifying the gender or age of cadavers, a chronical illness that may trigger CTS, a neurological table, uncertainty of etiologic factors like wrist trauma, and an insufficient number of participants in some studies.[4],[12],[27],[28] Using the Cavalieri method, a practical, fast, and quantitative examination about morphological changes on wrists became possible.[34] Obtaining volume and volume ratio data using MRI images, being one of the first studies to determine the diagnosis and severity of Carpal tunnel syndrome, and the specificity of the working operator reveal the strengths of our study. The situations that limit our study are deficient for reaching the intended number of cases according to the nonexistence of a routine MRG protocol in CTS, scanning each person in the same MR device, and excluding people that have bad quality MRIs.


  Conclusion Top


This study may be extended more by increasing the number of cases as men and women to analyze the volume and the volume fraction of the carpal tunnel, the contents, and free space fractions over wrist positions (flexion, extension, and neutral) depending on the CTS severity. The studies on Doppler USG and MRI reviewing the CTS severity are important for obtaining standard data. In this present study, CTVs and the structures within (median nerve and tendons) and the fraction values of these contents to the tunnel were analyzed for the first time.

According to our results, it has been observed that estimating CTV is a successful method in determining the susceptibility to CTS. As the severity of CTS increases, the difference between the median nerve volume and volume fraction increases and the free space of the carpal tunnel decreases. Thus, it was anatomically confirmed that as the severity of CTS increases, the free space of the carpal tunnel decreases. Consensus on diagnostic criteria for CTS is essential in clinical areas to provide effective treatment. The use of stereological techniques may also play an essential role in exploring the morphology of the carpal tunnel and cases that are difficult to diagnose.

Financial support and sponsorship

This study was supported by Ondokuz Mayıs University Graduate Student Research Projects Fund (Project No. PYO.TIP. 1904.11.004.). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflicts of interest

There are no conflicts of interest.



 
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
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