|Year : 2011 | Volume
| Issue : 2 | Page : 50-54
The morphological study of adult human larynx in a Western Indian population
Mohini M Joshi1, Sharda S Joshi2, Subhash D Joshi2
1 Department of Anatomy, Rural Medical College, Pravara Institute of Medical Science, Loni, Maharashtra, India
2 Department of Anatomy, Arbindo Institute of Medical Sciences, Indore, Madhya Pradesh, India
|Date of Web Publication||19-Sep-2011|
Mohini M Joshi
Department of Anatomy, Rural Medical College, Pravara Institute of Medical Science, Loni, Maharashtra
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Knowledge of the size and proportions of the human larynx is essential for the diagnosis and treatment of laryngeal disorders. Objective of the present cadaveric study was to study dimensions of larynx, various laryngeal folds and laryngeal cavity of adult human larynx in the western Indian population. Materials and Methods: Sagittal section of the head and neck region was taken from the cadaver. Larynx was separated from tongue from the level of hyoid bone to 3 rd tracheal ring. The measurements of intact and split larynx were taken with the help of digital vernier caliper, thread, and scale. Data was analyzed using software StatistiXL. For each of the parameters, the mean, standard deviation (S.D.), and range was calculated. Z test was used to test the significance of difference between the two mean. Results: Height of larynx from floor of thyroid notch to lower margin of cricoid cartilage was 32.42 ± 3.41 mm. Height of larynx from upper border of hyoid to lower border of cricoid. (L2) was 54.39 ± 6.04 mm. Height of larynx from tip of epiglottis to lower margin of cricoid cartilage was 57.13 ± 7.32 mm. Total height of laryngeal cavity was 61.51 ± 6.84 mm. Bilateral symmetry was noted in the size of vocal and vestibular folds length. Conclusion: There was wide individual variation in the dimensions of the most of the parameters in the selected population. Bilateral asymmetry, though present in majority of specimens, was insignificant. Morphometrical data of the larynx may be very useful in otorhinolaryngology, laryngeal microsurgery, and evaluation of results of diagnostic techniques. These parameters can be helpful in evaluation of the damage and proper repair of the larynx.
Keywords: Human, larynx, morphology
|How to cite this article:|
Joshi MM, Joshi SS, Joshi SD. The morphological study of adult human larynx in a Western Indian population. J Laryngol Voice 2011;1:50-4
| Introduction|| |
The larynx is essentially a cartilaginous tube that connects inferiorly to the respiratory system and superiorly to the vocal tract and oral cavity. A phonatory larynx is present in many animals and is used for communication between members of the same species.  Morphometrical evaluation of the larynx has always been interesting for both morphologists and the physicians. Dimensions of the larynx should be known for the procedures, such as intubation, stenting, cricothyroidotomy and for transplantation. From embryologic, anatomic, physiologic and surgical standpoints, the larynx is one of the most complex organs of human body.  Tayama et al., (2001) attempted to define and measure some biomechanically important morphometric features of the laryngeal framework of both human and canine larynx.  Zielinski (2001) studied clinically important laryngeal diameters from cadavers of both sexes.  Sprinzl (1999) studied measurement of cartilaginous larynx.  Ajmani (1980) has made various measurement of laryngeal cartilages in Indians.  Morphometrical study of cricoid and thyroid cartilages was done by Pereira et al.,  Zrunek et al., (1988) had compared the dimensions of the adult laryngeal skeleton of man and sheep.  Kahane et al., (1982) studied linear and weight measurements of Caucasian prepubertal and pubertal cadaveric larynges.  Hirano et al., (1989) investigated asymmetry of the human laryngeal framework.  Litman et al., (2003) carried out the measurement of transverse and anteroposterior laryngeal dimensions.  Eckel et al., (1994) studied the internal diameter of the cricoid cartilage and the angle of the laminas of the thyroid cartilage in larynx of German origin.  Cicekcibasi et al., (2007) studied morphometric growth patterns of the cartilaginous components and vocal cords.  Kim et al., (2004) had compared human, canine, and ovine laryngeal dimensions. 
Understanding the morphology of the laryngeal framework is a crucial step in elucidating the detailed laryngeal anatomy and physiology. While going through the literature we have come across the fact that there is paucity of literature on this important subject amongst the Western Indian population. Most of the previous studies focused on specific questions related to the measurement of the laryngeal cartilages, ,,,,, glottic region,  and subglottic larynx  Hence, the objective of the present cadaveric study was to study dimensions of larynx, various laryngeal folds, and laryngeal cavity of adult human larynx in the Western Indian population.
| Materials and Methods|| |
The present study was carried out in the department of Anatomy of a medical university teaching hospital. We used donated and unclaimed dead bodies for the purpose of medical education and research including anatomical examination under the Bombay Anatomical Act, 1949. The study was approved by the institutional Ethical and Research committee. The study was carried out during the period of June 2007 to June 2009. The sample consisted of 50 laryngeal preparations from adult cadavers. Forty seven specimens of larynxes were from males and three from females. The age range varied from 59 to 78 years, with an average age of 67.5 years. Laryngeal specimens, excised from cadavers with any possibilities of laryngeal damage as a result of diseases, diagnostic, or manipulation were not taken into consideration. Sagittal section of the head and neck region was taken from the cadaver. Along with the tongue, the specimen of the larynx was removed by cutting the muscles of soft palate, muscles of posterior pharyngeal wall and fascia. Larynx was separated from tongue from the level of hyoid bone to 3 rd tracheal ring. Dissection was performed using standard dissecting instruments under magnification with the help of hand lens and dissecting microscope (OPMI 99; Zeiss, New York). The measurements were taken with the help of digital vernier caliper (Mitutoyo, Japan) to the nearest 0.01 mm [Figure 1].
The following measurements were taken:
1) Intact larynx [Figure 2],[Figure 3]:
|Figure 2: L1: Height of larynx- from thyroid notch to lower margin of cricoid cartilage. L2: Height of larynx-from upper border of hyoid to lower border of cricoid|
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|Figure 3: L3: Height of larynx-from tip of epiglottis to lower margin of cricoid cartilage|
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- Height of larynx- from thyroid notch to lower margin of cricoid cartilage. (L1)
- Height of larynx- from upper border of hyoid to lower border of cricoid. (L2)
- Height of larynx- from tip of epiglottis to lower margin of cricoid cartilage. (L3)
2) Length of aryepiglottic folds: Length of aryepiglottic fold was measured from its upper attachment to the side of epiglottis to the apex of arytenoid with the help of digital vernier caliper.
3) Maximum height of aryepiglottic folds: Height of aryepiglottic fold was measured form midpoint of the length of aryepiglottic fold up to the lateral edge of vestibular fold with the help of digital Vernier caliper.
4) Interarytenoid fold: It is transverse mucosal fold between two arytenoid cartilages. Maximum height and width of interarytenoid fold was measured with the help of digital vernier caliper.
Posterior wall of the larynx was split in the median plane and the two sides held apart [Figure 4].
5) Height of three segments of laryngeal cavity was measured with the help of digital vernier caliper.
- Vestibule: It is space between laryngeal inlet and vestibular folds. Height of vestibule was measured from midpoint of the free end of the epiglottis up to the vestibular fold.
- Sinus: It extends from rima vestibule above to the rima glottidis below.
- Infraglottic cavity: It extends from the vocal folds to the lower border of the cricoid.
- Total height: It was measured from midpoint of the free end of the epiglottis up to the lower border of cricoid.
6) Length of vocal fold: The vocal fold extends from midlevel of thyroid angle to the vocal processes of arytenoids. The length of vestibular fold was measured with help of thread and scale.
7) Length of vestibular fold: The vestibular fold was extending anteriorly from the thyroid cartilage and posteriorly to the arytenoid cartilage. The length of vestibular fold was measured with help of thread and scale.
Data was entered into Microsoft Excel (Microsoft Corporation) and analyzed using software StatistiXL version 1.8 (statistiXL, Australia). For each of the parameters, the mean, standard deviation (S.D.), and range (minimum value-maximum value) was calculated. Z test was used to test significance of difference between the two mean. If the Z value is less than 1.96; then p value will be >0.05, the observed difference between two means is said to be statistically not significant. If the Z value is more than 1.96; then p value will be <0.05, the observed difference between two means is said to be statistically significant.
| Results|| |
In present study the height of larynx from floor of thyroid notch to lower margin of cricoid cartilage (L1) was 32.42 ± 3.41 mm. Height of larynx from upper border of hyoid to lower border of cricoid. (L2) was 54.39 ± 6.04 mm. Height of larynx from tip of epiglottis to lower margin of cricoid cartilage (L3) was 57.13 ± 7.32 mm. A fair amount of intersubject variability in the dimensions was observed. The average measurements of the larynx are listed in [Table 1].
It can be seen from [Table 2] that mean height of vestibule (32.11± 5.77) was more than the height of infraglottic cavity (23.05 ± 3.13). Total height of laryngeal cavity was 61.51 ± 6.84 mm. Difference between height of sinus on right and left side was not statistically significant. (z value = 0.48, p value = 0.62)
The vocal fold length varied from 9-25 mm on both sides. The vestibular fold length varied from 10-24 mm on both sides. Bilateral symmetry was noted in the size of vocal and vestibular folds length.
Average width (18.92 ± 3.30) of interarytenoid fold was more as compared to average height (15.18 ± 2.73).
The morphological data showed no significant asymmetry between the left and right sides (p > 0.05).
| Discussion|| |
The results provide a full scale of data determining the size and extent of the laryngeal framework as a whole. In present study the height of larynx from floor of thyroid notch to lower margin of cricoid cartilage (L1) was 32.42 ± 3.41mm. Height of larynx from upper border of hyoid to lower border of cricoid (L2) was 54.39 ± 6.04 mm. Height of larynx from tip of epiglottis to lower margin of cricoid cartilage (L3) was 57.13 ± 7.32 mm [Table 1]. The findings of present work are in agreement with those described by Jain et al., (2008) in Haryana, where the height of larynx from floor of thyroid notch to lower margin of cricoid cartilage was 33.47 ± 4.1 (31-39) in males and 31.2 ± 4.6 mm (24-39) in females.  But Ajmani (1990) observed higher height of larynx from floor of thyroid notch to lower margin of cricoid cartilage in Nigerians, where it was 45.06 ± 8.41 in males and 38.08 ± 8.25 mm in females.  No obvious explanation has been given by this author for this great disparity in the values. In a study by Kim et al., (2004) main height of ovine larynx (38.74 ± 2.72 mm) was significantly higher than the height of human and canine larynges because of vertically elongated ovine thyroid cartilage. 
It can be seen from [Table 2] that average height of infraglottic cavity was 23.05 ± 3.13 mm. The height of vestibule varied from 16.68-42.23. Height of sinus was 2.87 ± 1.37 mm on right side and 2.74 ±1.30 mm on left. Total height of laryngeal cavity was 61.51 ± 6.84 mm. Similar to present study Zelinski et al., (2001) reported height of infraglottic cavity 25.90 ± 3.80 in male and 22.18 ± 3.67 mm in female.  In same study Zelinski et al., (2001) observed that the height of laryngeal vestibule in median line varied from 31.14-49.2 in males and 29.2-40.3 in females.  The higher values in this study could be due to fact that in the median line it would include the height of epiglottis also.
In the present study, the vocal fold length varied from 9-25 mm on both sides and mean length of vocal fold was 14.86 ± 3.39 mm on right side and 14.84 ± 3.40 mm on left. The vestibular fold length varied from 10-24 mm and mean length of vestibular fold was14.89 ± 3.03 mm on right side and14.92 ± 2.98 mm on left [Table 3]. Hesham et al., (2005) endoscopically measured length of vocal fold in Egyptian population. The length of vocal fold varied from 11-26 mm. The mean length of vocal folds was 18.74 ± 3.71 mm.  The laryngeal framework was asymmetric to a greater or lesser extent in all larynges. Similarly Hirano et al., (1989) reported that the degree of asymmetry did not differ among different age groups and there was directional preponderance in asymmetry. He concluded that there must be some compensatory mechanisms for the asymmetric framework to keep the vocal fold edges relatively symmetric. 
Average width of interarytenoid fold was 18.92 ± 3.30 mm and average height was 15.18 ± 2.73 mm that is the width was greater than the height [Table 4]. The length of aryepiglottic fold was 16.43 ± 3.06 mm of right side and 15.85 ± 3.03 mm of left, while height of aryepiglottic folds was 17.94 ± 2.58 mm of right side and 17.64 ± 2.57 mm of left side [Table 5]. The morphological data showed no significant asymmetry between the left and right sides (p > 0.05). No comparable data was available in the literature reviewed.
The laryngeal framework was asymmetric to a greater or lesser extent in all larynges. Comparison of present observations with other populations reveals that the absolute values differ in different populations which could be due to differences in body built and racial differences.
Though a lot of information has been generated in the study, there are some lacunae worth mentioning. The predominant samples of larynges being of males, the data does not allow a satisfactory comparison of measurements based on sex. Also, the ethnicity of specimens could not be a study parameter due to paucity of data about the cadavers and limited numbers. Nevertheless, the present study presents important data about laryngeal dimension in the scarce data available about the Western Indian population morphology.
| Conclusion|| |
This study provides a comprehensive and detailed description of the dimensions of the adult human larynx in the western Indian population. There was wide individual variation in the dimensions of the most of the parameters. Bilateral asymmetry, though present in majority of specimens, was insignificant. Morphometrical data of the larynx may be very useful in otorhinolaryngology, laryngeal microsurgery, and evaluation of results of diagnostic techniques.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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