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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 71  |  Issue : 3  |  Page : 225-233

The normal vermiform appendixin adults: its anatomical location, visualization, and diameter at computed tomography


1 Department of Radiology, Faculty of Medicine, Gaziosmanpasa University, Tokat, Turkey
2 Department of Statistics, Faculty of Medicine, Gaziosmanpasa University, Tokat, Turkey

Date of Submission20-Sep-2019
Date of Acceptance21-Dec-2021
Date of Web Publication20-Sep-2022

Correspondence Address:
Prof. Aysegul Altunkas
Department of Radiology, Faculty of Medicine, Gaziosmanpasa University, Tokat
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JASI.JASI_135_19

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  Abstract 


Introduction: The anatomic location of the appendiceal tip is not certain and it may extend to the retrocecal, pelvic, subcecal, paracecal, postileal, or preileal positions. Its positional variations may alter the degree of inflammation and lead to further illness diagnoses such as colitis, ureteric colic, or pelvic inflammatory disease. Increase in appendiceal diameter is very important regarding the diagnosis of appendicitis. Therefore, the determination of cut-off values for normal appendiceal diameter in computed tomography (CT) would aid in ruling out appendicitis in suspected cases. We aimed in this study to evaluate the frequency of visualization and determine the location and diameter of the normal appendix on CT. Material and Methods: We scanned 1842 abdominal CT that were performed in our hospital for any reason, retrospectively. A total of 597 patients were excluded with various indications. Results: Lower-upper abdominal CT examinations of a total of 1245 patients were evaluated, and the appendix could be visualized in 984 patients (79%). The appendiceal diameter was ranged between 2.7 mm and 10 mm and it was >6 mm in 19% of the patients. The most common location of the appendiceal tip was pelvic in 318 (32%) appendices. The appendiceal tip was subcecal in 222 (23%), retrocecal in 180 (18%), postileal in 180 (18%), preileal in 54 (6%), and paracaecal in 30 (3%) appendices. Discussion and Conclusion: This study showed that the most frequent location of the normal appendix is pelvic type both in women and men.

Keywords: Computed tomography, location, variation, vermiform appendix


How to cite this article:
Altunkas A, Aktas F, Ozmen Z, Albayrak E, Demir O. The normal vermiform appendixin adults: its anatomical location, visualization, and diameter at computed tomography. J Anat Soc India 2022;71:225-33

How to cite this URL:
Altunkas A, Aktas F, Ozmen Z, Albayrak E, Demir O. The normal vermiform appendixin adults: its anatomical location, visualization, and diameter at computed tomography. J Anat Soc India [serial online] 2022 [cited 2022 Sep 29];71:225-33. Available from: https://www.jasi.org.in/text.asp?2022/71/3/225/356490




  Introduction Top


The vermiform appendix is a tube-shaped muscular organ localized to the right lower abdominal quadrant, which contains an abundance of microscopic lymphoid tissue.[1] Its length varies from 2 to 20 cm and is 9 cm on average. It stems from the posteromedial wall of the cecum 2 cm below the ileocecal junction, or closer to it.[2] Appendix is connected to a peritoneal fold called the mesoappendix, which carries its own arterial structures, and the length of this mesenteric structure differs according to sex and age.[3] The inadequacy of mesoappendix to supply the tip of the organ may lead to early perforation of this part in case of inflammation.

The vermiform appendix is the only organ in the human body that has an indefinite anatomical position. Its ultimate location is influenced by the changes occurring in the cecum during its growth and development.[4] Since anterior and lateral walls of the cecum grow faster during its development, the orifice of the vermiform appendix is often localized at the posteromedial side of the cecum. The tip of the appendix may be found in any one of the following positions retrocecal, pelvic, subcecal, paracecal, postileal or preileal.[5]

Localization of the appendix has been a topic of interest, not only because of its developmental significance but also because of its pathological and surgical importance. Location of vermiform appendix is important in terms of diagnosis and prognosis of appendicitis, and the surgical approach to it. Variations in its position may alter the degree of inflammation, and clinical presentation of appendicitis as well. Indeed, retrocecal appendicitis may mimic colitis; postileal appendicitis may mimic ureteric colic, pelvic inflammatory disease, and ovarian cyst torsion; and subhepatic appendicitis may mimic hepatitis and biliary colic. Misdiagnosis rates are 10%–33% in various age groups.[6] Thus, awareness of the positional variations of appendix may prevent misdiagnosis.

Various studies have shown differences between populations in terms of appendix position.[7] These studies have often been conducted on either autopsied bodies or cadavers or by evaluating patients undergoing surgical operation. A careful review of the studies related to the localization of the appendix reveals some methodological errors. Following death, all muscles in the body, including the smooth muscles of the intestines display some changes such as primary flaccidity, rigor mortis, and secondary flaccidity.[8] Furthermore, the formaldehyde that is used for cadaveric fixation has a shrinking and distorting effect on tissues.[9] Considering the effects of these postmortem changes and formaldehyde fixation on the internal organs, data from the autopsy and cadaveric studies related to localization of appendix have limited credibility. On the other hand, surgical studies have usually determined appendix localization in patients undergoing appendectomy. Since appendix is swollen (edematous) in patients with appendicitis, and therefore, can be displaced with gravity, it is obvious that surgical studies cannot provide accurate data on normal appendix position. For this reason, it is very important to establish the normal position of appendix in living and healthy individuals intraabdominal via radiological studies.

Demonstration of the normal appendix in computed tomography (CT) would aid to rule out the diagnosis of appendicitis in suspicious cases.[10] For this reason, studies that evaluate normal appendix with radiological examinations have great clinical significance. While there are many studies that were conducted to establish CT criteria for appendicitis, studies that evaluate normal appendix with CT images are few and show contradicting results. Apart from the study by Lee et al.,[11] these studies were generally conducted on small sample sizes. Therefore, we have designed our study to include the largest number of participants. In addition, apart from the studies by Picken et al.[12] and Lee et al., the classification of appendix locations in all other radiological studies do not allow comparison with the classical classification system commonly used in anatomical, autopsy, and surgical studies.

The aims of our study were: (1) to evaluate the frequency of visualization of the normal appendix on CT, (2) to determine the location and diameter of the normal appendix, (3) to assess whether gender, age, or administration of contrast material (IV, IV + oral) before CT examination had any influence on these parameters.


  Material and Methods Top


Study population and design

This research received approval from our institution's Clinical Research Ethics Committee. In our study, which has a retrospective study design, we scanned 1842 abdominal CT examinations that were performed in our hospital from January 2014 to January 2015 for any reason [Figure 1]. Pediatric patients and patients with appendicitis or any other intraabdominal pathology (ascites, abscess, postoperative early period, etc.) were not included in the analysis. After exclusion of 597 patients, lower-upper abdominal CT examinations of 1245 patients were evaluated, and appendix could be visualized in 984 patients (417 female, 567 male; age range: 18–89 years; mean age: 51 ± 16 years). For those patients, whose appendix could not be visualized, patient record system was investigated to determine whether these patients had a previous appendectomy operation. If there was no information available on the system, patients were phoned to retrieve this information. Thus, a total of 984 patients whose appendix could be visualized were accepted as having normal appendix, and appendiceal diameter and localization were evaluated in these patients.
Figure 1: The study flowchart

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Computed tomography examination and image analysis

All evaluations were performed with spiral CT (LightSpeed Ultra; GE, Milwaukee, United States), using a section thickness of 5 mm, intersection gap of 5 mm, and pitch of 0.875:1. In all scans, 120 kVp and 100 mA values were selected. The scans were performed in the supine position, starting from a level above the liver to the end of the urinary bladder, while patients holding their breath. In some patients, intravenous (IV) and oral contrast agents were administered. Oral contrast agent (1000–1500 mL; 2% barium suspension) was given approximately 1 h before the scan. IV contrast agent (120 mL; nonionic contrast substance) was administered as IV bolus injection, with a rate of 2 mL/s. Of all the examinations included in the study, 38% (390) were without contrast administration, 32% (322) were with IV contrast administration, and 30% (295) were with IV + oral contrast administration. None of the patients received rectal contrast administration. While axial images were the source images, multiplanar reformat images were also used.

Picture Archiving Communication Systems network was used for localizing appendix and measuring its thickness. CT scans were retrospectively evaluated by two radiologists with more than 10 years of experience in abdominal imaging. For patients, whose appendix could be visualized, appendix thickness and location were noted. In the absence of intraluminal content in appendix, appendiceal thickness was measured as the double wall thickness. In the presence of intraluminal content, measurement was performed from one wall to the other (maximum full-thickness) [Figure 2]. Appendix localization was classified based on the position of the tip of the appendix. Accordingly, appendix was classified as “retrocecal” if the tip of appendix was localized posterior to the cecum, “subcecal” if the was localized inferior to the cecum, “paracecal” if the tip was localized lateral to the cecum, “pelvic” if the tip extended to the pelvis, “postileal” if the tip was localized posterior to the ileum, and “preileal” if the tip was localized anterior to the cecum.
Figure 2: (a) The appendiceal diameter (arrow) was determined by measuring the double wall thickness, since the intraluminal content was not recognizable. (b) If content was recognizable, the maximum full thickness (arrow) was measured and it was accepted as diameter

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Statistical analysis

Statistical analyses were performed using the SPSS package program (IBM-SPSS 20, Chicago). Data were expressed as mean ± standard deviation. The association of visualization and localization frequency of appendix with sex and contrast administration was analyzed with Chi-square test. Comparisons between different sexes and contrast and noncontrast groups in terms of appendiceal diameter were made with Student's t-test. P < 0.05 was accepted as statistically significant.


  Results Top


The appendix was visualized in 79% (984/1245) of the patients. This rate was 76% (417/551) in females and 82% (567/694) in males, and there was no significant difference between the different sexes in terms of visualization rate of appendix (P = 0.712). In addition, appendix visualization rate did not show a significant difference in comparison to noncontrast, IV contrast and IV + oral contrast CT scans (P = 0.227).

Mean appendiceal diameter was 5.28 ± 0.99 mm (ranged between 2.7 and 10 mm) [Table 1] and [Figure 3]. Appendiceal diameter was >6 mm in 19% of the patients (female: 18%; male: 20%) [Figure 4]. Mean appendiceal diameter was 5.24 ± 1.01 mm in females and 5.31 ± 0.97 mm in males. Appendiceal diameter did not show a significant difference between different sexes or groups based on contrast administration (P = 0.147 and P = 0.212, respectively).
Table 1: Diameter of the normal appendix on computed tomography

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Figure 3: Scatter diagram showing statistically significant but low-degree negative correlation between the age of the subject and the diameter (r = 0.129, P = 0.002)

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Figure 4: Frequency distribution of the diameter of the normal appendix

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In all patients, the most common location of the appendiceal tip was pelvic in 318 (32%) of 984 appendices. The appendiceal tip was subcecal in 222 (23%), retrocecal in 180 (18%), postileal in 180 (18%), preileal in 54 (6%) and paracaecal in 30 (3%) appendices [Table 2], [Figure 5] and [Figure 6]. Location of appendix did not show significant difference between sexes, or groups based on contrast administration (P = 0.349 and P = 0.285, respectively). The differences between the relative frequency of the male and female subgroups for different appendix locations were as follows: pelvic (male: 29% vs. female: 37%, P = 0.325); subcecal (male: 24% vs. female: 20%, P = 0.655); retrocecal (male: 20% vs. female: 16%, P = 0.505); postileal (male: 18% vs. female: 18%, P = 1.000); preileal (male: 6% vs. female: 5%, P = 0.808); and paracaecal (male; 3% vs. female; 4%, P = 0.537) [Table 2].
Table 2: Location of the appendiceal tip according to gender

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Figure 5: Locations and relative frequencies of the normal appendix

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Figure 6: Computed tomography scans of different locations of the appendiceal tip. Axial image shows an appendix extends into the pelvis (a), paracecal (b) and posteriorof the terminal ileum (c). Axial image demonstrates a retrocecal appendix is located posterior to the cecum (d)

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  Discussion Top


CT is currently the main imaging method used to assess patients with acute appendicitis. Only 60% of appendicitis cases have clinical manifestations, and pelvic pathologies can mimic acute appendicitis; therefore, if the diagnosis is based on clinical findings alone, it is likely to get quite high negative appendectomy rates, reaching rates around 20% especially in women.[13],[14],[15],[16] Utilization of CT examinations for diagnosis of appendicitis has made ruling out the other causes of acute abdomen easier and significantly reduced the negative appendectomy rates.[17]

Diagnostic CT criteria for acute appendicitis include appendiceal diameter over 6 mm, demonstration of calcified appendicolith, and observation of periappendiceal inflammatory changes.[18] In their study, Jacobs et al.[19] reported that, in their CT scans, 22% of patients with appendicitis did not show stranding sign that is formed by periappendiceal inflammatory changes and the surrounding fat tissue. Moreover, “periappendiceal fat stranding” in CT can be observed in 3%–7% of normal individuals.[20] In addition to these, appendicolith is not only observed in appendicitis cases but can also be detected in 2%–8% of normal individuals.[21],[22],[23] Therefore, measurement of appendiceal diameter is very important regarding the diagnosis of appendicitis, and previous studies have shown that increase in appendiceal diameter is the most sensitive and specific diagnostic criteria.[24] However, the established cut-off values for normal appendiceal diameter are based on the diagnostic criteria determined by ultrasonography (USG) studies.[25],[26],[27]

During USG examination, the lumen is often obliterated due to the compression exerted on the anterior abdominal wall. For this reason, many researchers believe that USG criteria cannot be adapted to CT images. In our study, appendiceal diameter was measured as the maximum outer diameter, and 19% of the study participants had appendiceal diameters over 6 mm. Other studies that evaluated appendix with CT also reported that 17%–59% of healthy individuals had appendiceal diameter over 6 mm.[28],[29] Due to these high rates observed in normal individuals, the researchers noted that it was necessary to raise the upper limit of normal appendiceal diameter from 6 mm to 10 mm.[30],[31] Consistent with this proposal, normal appendiceal diameter was not over 10 mm in any of our cases. Furthermore, only 5 cases (0.5%) in our study had an appendiceal diameter over 8 mm. Our findings indicate that in case the appendiceal diameter is measured using the maximal outer diameter method in CT examination, a cut-off measurement value of 8 mm can be used conveniently for discriminating between normal appendix and appendicitis. Nonetheless, since 0.5% of normal individuals have appendiceal diameter above 8 mm, relying on appendiceal size measurement alone without consideration of clinical and laboratory findings for the diagnosis of appendicitis may lead to misdiagnosis and wrong treatment.

Demonstration of normal appendices in CT would aid in ruling out appendicitis in suspected cases. This is especially the case for patients who are suspected to have appendicitis but in fact have another abdominopelvic pathology as the cause of patient's symptoms. In these patients, the picture is further complicated if this alternative etiology does not reveal any signs in CT. In such complicated cases, demonstration of normal appendix in CT would direct the physician away from the diagnosis of appendicitis, and guide him/her for further examination aimed at the alternative etiology. Therefore, it is very important to have knowledge about the appearance, location, size, visualization rate, and other characteristics of the normal appendix in CT scan.[32] A review of the studies related to the visualization rate of the normal appendix in CT shows us that this rate has displayed a profound increase in parallel with the advances in CT technology over the years. Normal appendix can be visualized in the rates of 40%–50% with conventional CT,[33],[34] 70%–80% with spiral CT[35],[36] and up to 90%–95% with multidetector CT (MDCT).[37] In our study, appendix could be visualized in 79% of normal individuals without appendicitis, which is a consistent finding with the previous spiral CT studies.

Oral and/or IV contrast administration is frequently used in CT examination to aid in the visualization of normal appendix and diagnosis of appendicitis.[38] It was believed that oral contrast administration would opacify the appendiceal lumen and IV contrast agent would make the appendiceal wall more recognizable so that it would be easier to visualize appendix, particularly in normal individuals. However, results from the related studies do not support this view. In our study, we found that contrast administration in spiral CT did not cause a change in visualization rate of the normal appendix. Similarly, studies using either conventional or MDCT did not find any effect of IV or oral contrast administration on visualization rate of appendix. There are several disadvantages to oral contrast administration. It causes delayed transit times of up to 4 h; the appendiceal lumen can be filled only in a portion of patients; and its tolerability is low because it requires a large volume such as 1400 mL, and it causes nausea. On the other hand, IV contrast administration can lead to adverse effects (e.g., allergic reactions) at a rate of 0.5%–4%, and brings an additional cost as well.[39],[40] For this reason, there is a tendency toward the use of noncontrast CT scan today.

The increased image quality provided by MDCT technology renders contrast administration less and less preferable.[41] A review of studies on contrast and noncontrast (unenhanced) MDCT examinations shows that visualization rates are similar with both, which supports this view. Although MDCT is becoming increasingly available, spiral CT is still used commonly, and it is still the most frequently used CT in many countries.[42] Therefore, it is very important to determine whether contrast administration is necessary with spiral CT for visualization of normal appendix, and thus, ruling out the diagnosis of appendicitis. Considering the uncontrollable factors (patient characteristics, scanning protocol, radiologist's experience, etc.) in our study, further studies are necessary to confirm our results regarding contrast administration.

In our study, we did not find a significant difference between male and female sex in terms of visualization rate of the normal appendix. Negative appendectomy rates are reported to be twice as higher in women than in men (23% vs. 12%) because gynecological pathologies can mimic acute appendicitis. Therefore, visualization of the normal appendix is particularly important in women for ruling our appendicitis. Among previous studies related to visualization of the normal appendix, only four studies have examined the difference between female and male sex. Similar to our results, three of them did not find any difference between the sexes, whereas one study reported lower visualization rate in women.[43],[44] Our study includes a larger sample size, which is considered as a strength of our study, increasing the credibility of our results. In light of our findings, CT examination in women for ruling out the diagnosis of appendicitis is as effective as in men.

If we categorize the previous studies examining the appendix location as anatomical (cadaveric), radiological, surgical, autopsy, and mixed studies, we see that retrocecal position was the most frequent location in all the anatomical studies [Table 3] and [Table 4]. Anatomical studies use cadavers that are prepared in formalin (PF-Cadavers), and formaldehyde has shrinking and distorting effects on tissues; therefore, appendix position may be altered in these studies. Because of this bias, the credibility of the results from anatomical studies has dwindled. Similar to the effect of formaldehyde, due to the postmortem changes (primary flaccidity, rigor mortis, and secondary flaccidity) encountered in autopsy studies and edematous changes secondary to appendicitis encountered in the surgical studies, it is difficult to generalize the results of these studies to the general population, i.e., appendix in a healthy human.
Table 3: Major locations of the vermiform appendix reported in autopsy and cadaveric studies

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Table 4: Major locations of the vermiform appendix reported in surgical, mixed, and radiologic studies

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Our literature review yielded totally four mixed type studies evaluating PF-Cadavers, autopsied bodies, and operated patients together [Table 4]. Although these mixed-type studies presented no information on the percentage of PF-Cadavers among the total number of subjects evaluated, a bias caused by formaldehyde use is also apparent in these studies, as the most frequent appendix position was retrocecal.[45],[46],[47] Among the mixed type of studies, the study by Wakeley[48] stands out with its large sample size, which included 10,000 individuals. The results of this study have been used as reference in many textbooks, and thus, it became a common opinion that the appendix is usually found in retrocecal position. However, their results become less credible when we consider the effects of cadaveric fixation and postmortem changes occurring in the body. This view is further supported by the fact that none of the radiological studies, including ours, have found retrocecal position as the most frequent location as proposed by Wakeley.

Radiological studies related to the localization of appendix have often used USG, MRI and CT. Retrocecal appendix cannot be evaluated with USG, and excess abdominal fat mass hampers evaluation with USG, which are the main limitations to the utilization of USG.[49] MRI is not a commonly used method due cost-effective reasons, therefore studies that examine appendix position in adults with MRI are quite few. For these reasons, studies on the localization of appendix have often used CT. We also preferred CT in the present study, and based on the position of the appendiceal tip, we found the most frequent appendix location as pelvic position (32%). Similarly, Turkoglu et al. and Willekens et al. also found pelvic position as the most frequent location, in the rates of 47% and 66% respectively. Unlike these studies, there are some other CT studies which reported the most frequent appendix position as paracolic, subcecal, or postileal [Table 4].

Methodological differences like the type of the CT used (classical, helical, or multidetector), section thickness and intersection gap, patient groups included in the study, the age range of participants, and whether contrast is administered or not make it difficult to compare our results with the other CT studies. Another factor that complicates the comparison between the studies is that different classification criteria were used for the localization of appendix. While some researchers used their own new classification systems, others preferred to use a modified classification. This makes it impossible to make comparisons between radiological studies and other types of studies in terms of position frequency. Only three CT studies including the present one used a classical classification system that has been commonly used in anatomical and autopsy studies. The most frequent appendix positions found in these three studies were retroileal in the study by Pickenet et al., subcecal in the study by Lee et al., and pelvic position in our study.

The main reasons why appendix can be observed in so much various positions in CT images can be listed as (1) variations in mesoappendix and in cecum position, (2) the effect of appendiculoovarian ligament, (3) the level of peritoneal reflection line at the posterior surface of the cecum, (4) interindividual variations in appendiceal length, (5) presence of fetal type of appendix, (6) variations in origin of the appendiceal ostium, and (7) the fact that appendix can develop while adhered to the cecum or posterior abdominal wall. For example, pelvic-type appendix occurs more likely when cecum is positioned more inferiorly than normal (close to iliac vessels) or when the appendix has a long mesoappendix. In addition, if the mesoappendix originates from the anterior side instead of the posterior side of cecum, backward movements of the appendix would cause excess tension in the mesoappendix, which would prevent appendix from having a retrocecal position. Furthermore, if the peritoneal reflection line at the posterior side of the cecum is positioned too low, formation of retrocecal fossa would be prevented, and this would result in appendix not having a retrocecal position. To have a better understanding of the appendix position, further studies planned in a multi-center setting that will take all these factors into consideration and use a similar classification system are necessary.

Some authors suggested that appendix can move freely around the cecum with a “free-floating” motion, and therefore it does not stay in a fixed position in any individual.[50] It has also been proposed that appendix may move to different positions throughout the day or at different times in each person, influenced by the fullness state of cecum and changes in body position.[51],[52],[53] In our review of the literature, we did not encounter any study on this subject. Therefore, further studies evaluating CT images of the same person scanned at different times may clarify this topic.

The main limitation of the present study is the lack of surgical-pathological evidence for the normal appendix. However, since excision of appendices of normal individuals would not be ethically approved, patient history and CT findings were taken into consideration for accepting the appendix as normal. Another limitation is that anamnesis related to previous appendectomy operations was obtained from patients. In some patients who underwent pelvic operation due to another cause, it is possible that the normal appendix has been excised and the patient was unaware of it. In addition, ignorance of congenital absence of appendix is another limitation of our study. Nonetheless, the incidence rate of appendiceal agenesis has been reported as 1 in 100,000 (0.001%) in laparotomies performed for appendicitis, and as 6 in 100,000 (0.006%) in autopsies; therefore, this is not likely to cause a significant impact on our results.[54]


  Conclusion Top


We found the most frequent location of the normal appendix as pelvic type both in women and men. In addition, noncontrast CT was as successful as contrast CT for visualizing the normal appendix, and appendiceal diameter in CT was above the cut-off value of 6 mm in nearly one-fifth of the patients with normal appendix. Therefore, we believe it would be appropriate to raise this cut-off value of the normal appendiceal diameter to 8 mm for evaluation of appendix with CT.[80]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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