Morphometry of Adult Human Trachea and its Clinical Implications: A Cadaveric Study in Northern India

1. Junior Resident, Department of ENT, Government Medical College, Amritsar, Punjab, India. 2. Professor, Department of Anatomy, SGRDIMSR, Amritsar, Punjab, India. 3. Professor, Department of Anatomy, SGRDIMSR, Amritsar, Punjab, India. 4. Professor, Department of Anatomy, SGRDIMSR, Amritsar, Punjab, India.

Abstract

Introduction: There is a wide variation in different dimensions of trachea in same age group as well as in different age groups in both sexes. Besides anthropometry, the study of these morphometric variations is of profound clinical importance as it may help the pulmonologists to understand the aetiology of several pulmonary diseases like bronchitis, emphysema, pulmonary fibrosis and tuberculosis.

Aim: To determine the variations in the dimensions of human trachea in the cadavers of age group 20-70 years in Northern India.

Materials and Methods: This cross-sectional study was conducted in the Department of Anatomy, Sri Guru Ram Das Institute of Medical Sciences and Research, Amritsar, Punjab, India, during March 2019 to December 2021. A total of 40 tracheas were obtained from adult human cadavers which were included in present study by convenience sampling. The trachea was dissected with the larynx and principal bronchi and measurements were taken. Data collected was saved on Microsoft excel and was analysed by calculating percentages, mean and Standard Deviation (SD).

Results: Mean length of trachea was 109.25 mm, mean subcarinal angle was 75.45°. Mean anteroposterior diameter, transverse diameter, mean height and distance between posterior ends of rings was 16.70 mm and 18.10 mm, 4.53 mm and 12.15 mm respectively and mean of inter-ring distance between 1^st-2^nd, 5^th-6^th, 10^th-11^th, 15^th-16^th Tracheal rings was 1.12 mm.

Conclusion: The present study revealed a wide variation in different dimensions viz. length, transverse and anteroposterior diameters, mean height, inter-tracheal ring distance and the subcarinal angle. Accurate anatomical knowledge of the variations is essential for understanding the pathophysiology and management of different airway disorders and in reconstructive surgery of tracheobronchial tree.

Dimensions, Pulmonary fibrosis, Sleep apnoea, Subcarinal angle, Tracheal rings, Variations

The trachea is an unpaired hollow tube that descends as a continuation of the larynx from C6 to the upper border of T5 vertebra where it divides into right and left principal bronchi (1). There is a wide variation in different dimensions of trachea in same age group as well as in different age groups in both sexes (2),(3),(4),(5),(6),(7),(8). There is wide variation in dimensions of trachea described in different textbooks and by different authors in different journals (1),(9). Gray’s Anatomy by Standring states that adult trachea is 10-11 cm long, external transverse diameter is 2 cm in adult males and 1.5 cm in adult females, lumen has an average transverse diameter of 12 mm (1). Schwartz in Text book “Principles of Surgery” stated that range of tracheal length is 10-13 cm, 18-22 semicircular cartilage rings, 2.3 cm transverse diameter and 1.8 cm anteroposterior diameter (9).

Besides anthropometry, knowledge of morphometric variations is essential as it may help the pulmonologists to understand the aetiology of several pulmonary diseases like bronchitis, emphysema, pulmonary fibrosis and tuberculosis (10). The present study was taken up to measure different dimensions of trachea (length, subcarinal angle, anteroposterior and transverse diameter, height of rings and distance between posterior ends of tracheal rings) which can be helpful in pulmonary physiology and anaesthesiology to conduct some maneuvers like endotracheal intubation, diagnostic and therapeutic bronchoscopic procedures with skill and perfection. Though the study measuring the dimensions of trachea are available form different parts (3),(4),(5),(7),(11) but the studies related to this area are sparse. Hence, present study was conducted to determine the variations in the dimensions of human trachea in the cadavers of age group 20-70 years in Northern India.

Material and Methods

The present cross-sectional study was done on 40 tracheas obtained from adult human cadavers in the Department of Anatomy, Sri Guru Ram Das Institute of Medical Sciences and Research, Amritsar, Punjab, India, from March 2019 to December 2021.

Inclusion criteria: Adult human cadavers aged between 20-70 years were included.

Exclusion criteria: Cadavers aged more than 70 years and less than 20 years, mutilated cadavers, cadavers having sternal and tracheal deformities, Human Immunodeficiency Virus (HIV) and Corona positive cadavers were excluded.

Sample size: A total of 40 trachea, obtained from adult human cadavers were enrolled for the study by convenience sampling.

Cadaver was placed in supine position on dissection table with extended neck. Skin incision was given from symphysis menti to xiphoid process of sternum. Lateral incision was given from symphysis menti along the lower border of mandible and from xiphoid process upwards and laterally along the floor of axilla. After reflecting skin, superficial fascia, deep fascia, muscles (sternohyoid, sternothyroid and sternocleidomastoid), the sternoclavicular joint was disarticulated, sternum was reflected downward after cutting the ribs at the costal cartilages with the bone cutter. Viscera like lungs, heart, thyroid gland were removed along with great vessels, nerves and prevertebral muscles. The trachea was dissected with the larynx and principal bronchi (11). The measurements were taken as follows:

Tracheal length: It was measured with vernier caliper from the lower border of cricoid cartilage to the apex of subcarinal angle where the trachea was bifurcating (Table/Fig 1).

Total number of tracheal rings were measured in the mid-sagittal line.

Subcarinal angle was measured with the help of thin wire and goniometer and was rechecked by protractor (Table/Fig 2).

Anteroposterior diameter of trachea was measured in the mid-sagittal plane and transverse diameter was measured in the mid-coronal plane with the help of Vernier caliper by taking horizontal section of trachea at the level of 1^st, 5^th, 10^th and 15^th tracheal rings (Table/Fig 3), (Table/Fig 4).

Height and distance between posterior ends of rings was measured with the help of vernier caliper at the level of 1^st, 5^th, 10^th and 15^th tracheal rings (Table/Fig 5).

Inter-ring distance between 1^st and 2^nd, 5^th and 6^th, 10^th and 11^th, 15^th and 16^th rings was measured in midline with the help of vernier caliper (Table/Fig 6).

In the specimens having less than 15 rings, measurements were taken only at the level of 1^st, 5^th and 10^th tracheal rings (12). Vernier calliper of the company airspace with least count 0.02 mm was used to measure length, breadth, height and diameter of the trachea.

Statistical Analysis

The data were statistically analysed for calculating the range, mean and SD using manual computation.

Results

In this study, 40 adult human cadavers were aged between 20-70 years. It was found that the range of tracheal rings was 14-19 and 17 was the most frequent value. The mean length of trachea from lower border of cricoid cartilage to carina was 105.25±6.03 mm, range being 90.50-121.20 mm.

Mean subcarinal angle was 77.45±13.15°, range being 47-122^o. Mean of inter-ring distance between 1^st-2^nd, 5^th-6^th, 10^th-11^th and 15^th-16^th tracheal rings was 1.12±0.51 mm and, range 0.10-3.50.

The mean anteroposterior dimension of trachea was 16.07 mm ranging from 8.90 to 23.75 mm and mean transverse diameter was 18.10 mm (ranging from 12.75 to 25.75 mm). Mean height of tracheal ring was 4.53 mm (ranged between 2.10-14.04 mm). in present study mean distance between posterior ends of rings was 12.15 mm (ranging from 5.30 to 24.80 mm) (Table/Fig 7), (Table/Fig 8).

Discussion

The mean length of trachea from lower border of cricoid cartilage to carina was 105.25 mm, range being 90.50-121.20 mm with standard Deviation 6.03. Strenberg (13) in the Text book of diagnostic surgical pathology 3^rd edition described the length of trachea to be 11 cms. Kamel KS et al., measured the length of trachea in vivo using high resolution chest CT scan in the age group of 22-88 and documented that the length was 102.8±9.9 mm (6). Munguia DA carried out a study of 44 Mexican cadavers in the age group of 18-65 years and found that tracheal length was 9.1±0.9 cm in males and 8.6±0.6 cm in females (7). Begum T et al., measured the length of 47 trachea of Bangladeshi adult males after dividing the cases into four age groups and found that mean length was 8.73±0.21 cm in group A (20-29 years), 9.53±0.46 cm in group B (30-39 years), 9.63±0.23 cm in group C (40-49 years) and 9.79±0.39 cm in group D (50-59 years), overall mean was 9.32±0.42 cm (14).

Regarding number of tracheal rings, Cinar U et al., (15) in their study on 75 male trachea and Kim IKS et al., (4) in their study on 33 male tracheas reported that the number of tracheal rings were 13.3±1.6 and 16.8±0.3 respectively. Rosen FS studied 50 specimens and observed that trachea on average contains 13.3 rings (16). Michael J told that for every two cms there were two rings (17). In the present study, the range of tracheal rings was 14-19 which was in accordance with the study of Kamel LS et al., (6), Munguia DA (7), Mridula C and Krishnaiah M (18), and Toremalm NG (19) who reported the range of tracheal rings was 14-19, 14-21, 14-24 and 14-20 respectively.

Kamel KS et al., measured subcarinal angle of bifurcation between first two cms of inferior wall of the right and left principal bronchi in 60 specimens using HRCT scans and reported that the range of angle was 36-121^o with mean 78±20^o (6). Haskin PH and Goodmann LR concluded that the mean subcarinal angle was 60.8±11.8^o in the radiographs of 47 males and 53 females in 21-80 years of age group (20). Chunder R et al., measured the subcarinal angle on the photograph along the inferior border of principal bronchi after dividing 87 cadavers (51 males and 36 females) into 5 age groups and reported that the mean angle in males was 64.3^o in 0-15 years, 56.4^o in 16-25 years, 58.4^o in 26-40 years, 57.1^o in 41-55 years and 59.5^o in more than 55 years of age (21).

As depicted in (Table/Fig 8), mean anteroposterior diameter, transverse diameter, mean height and distance between posterior ends of rings was 16.70 mm and 18.10 mm, 4.53 mm and 12.15 mm respectively and mean of Inter-ring distance between 1^st-2^nd, 5^th-6^th, 10^th-11^th and 15^th-16^th Tracheal rings was 1.12 mm. According to Standring S (1), the external transverse diameter of trachea is 2 cm in adult males and 1.5 cm in adult females while its internal transverse diameter is 1.2 cm in live adults. Kim IKS et al., in their study on 33 male Korean bodies reported anteroposterior and transverse diameter at the level of 1^st tracheal ring- 21.97±0.61 mm and 22.54±0.41 mm, 5^th ring- 22.40±0.48 mm and 20.84±0.51 mm, 10^th ring-19.85±0.40 mm and 20.60 0.35 mm, 15^th ring- 19.60±0.54 mm and 22.12±0.57 mm respectively (4). Kamel KS et al., in their study on 60 specimens using high resolution CT scans reported tracheal anteroposterior diameter from sagittal slices was 21.4±3.2 mm, range (12.7-28.6 mm) and transverse diameter from coronal slices was 25.7±3.7 mm, range (17.3-34.5 mm) (6). Munguia DA (7) in their study on 44 cadavers reported anteroposterior diameter in midsagittal plane was 1.8±0.3 cm, range (1.4-2.5 cm) and transverse diameter in mid-coronal plane was 1.9±0.2 cm, range (1.6-2.3 cm) (7). Mridula C and Krishnaiah M measured diameter of trachea in 16 patients with small peripheral pulmonary nodules at four horizontal positions by special window technique (window width 500 Hu, window level 100 Hu) and reported that tracheal diameter at thoracic entrance was 18.9±1.7 mm, at the level of aortic arch was 18.8±1.6 mm, at the level of two cms higher than carina of trachea was 19.0±1.6 mm and at narrowest trachea was 18.4±1.5 mm respectively (18). Strenberg (13) described the tracheal diameter as 2-2.5 cms. Chunder R et al., recorded upper external transverse diameter (width) and upper anteroposterior diameters (depth) at the junction of upper third and middle third of trachea in 51 male human trachea and reported that the results were 1.95 cm and 1.35 cm in 0-15 years, 2 cm and 1.6 cm in 16-25 y, 2.1 cm and 1.7 cm in 26-40, 2 cm and 1.6 cm in 41-55 Y, 2cm and 1.9 cm in >55 years age groups of males respectively (21). Lower external transverse diameter and lower anteroposterior diameters at the junction of middle third and lower third of trachea were 1.85 cm and 1.05 cm in 0-15 years, 2 cm and 1.6 cm in 16-25 years, 2.1 cm and 1.6 cm in 26-40 years, 2 cm and 1.5 cm in 41-55 years, 2.1 cm and 1.5cm in >55 years age groups respectively (21). Solanki S and Zarana A measured anteroposterior and transverse diameters of trachea on 28 cast of trachea prepared by luminal cast plastination and reported mean AP diameter was 1.70 cms (range 1.16-2.25 cm) and mean transverse diameter was 1.78 cm (range 1.42-2.1 cm) (22). Hampton T et al., reported that transverse diameter of trachea was 1.75±0.26 cm (23). Li C et al., observed Tracheal diameter 1.99 cms, range (1.2-2.5 cms) (24). Breatnach E et al., studied X-rays of 808 patients and found tracheal diameter 2.5-2.7 cms in males and 2.1-2.3 cm in females (25).

Regarding vertical height of tracheal ring, Kim IKS et al., reported vertical height of tracheal ring in 33 male specimens at the level of 1^st ring- 6.47±0.36 mm, 2^nd ring -3.71±0.19 mm, 5^th ring- 3.97±0.19 mm, 10^th ring- 4.31±0.18 mm, 15^th ring- 4.66±0.37 mm (4). Kamel KS et al., in their study on 10 cadavers reported the vertical height of tracheal ring 4.6±0.1 mm, range 2.3-12.2 mm (6). Munguia DA reported 4.5±0.3 mm, range 3.0 -9.0 in accordance with the present study where the vertical height in 40 specimens was 4.53±2.6 mm (7).

Kim IKS et al., reported inter- ring distance between 1^st and 2^nd was 1.98±0.19 mm, between 5^th and 6^th ring 1.63±0.11 mm, between 10^th and 11^th ring 1.61±0.16 mm, between 15^th and 16^th ring 1.81±0.20 mm (4). Kamel KS et al., (6) in their study on 10 cadavers noted that mean of inter -ring distance was 1.6±0.2 mm in accordance of present study where the mean of inter -ring distance 1.12±0.4 mm (6).

Kim IKS et al., (4) reported the distance between posterior ends of rings -at the level of 1^st ring 13.19±0.72 mm, 5^th ring- 11.61±0.84 mm, 10^th ring- 12.14±0.83 mm, 15^th ring -15.53±1.07mm. Present study showed distance between posterior ends of rings at the level of 1^st, 5^th and 10^th tracheal rings was 12.15±3.42 mm which was very near to the study of Kamel et al., (6) who reported the mean distance between posterior ends of rings at the level of 1^st, 5^th and 10th tracheal rings was 15.9±2.3 mm.

The comparison of parameters such as- tracheal length, subcarinal angle, antero-posterior and transverse diameter with previous studies are shown in (Table/Fig 9), (Table/Fig 10), (Table/Fig 11) (3),(4),(5),(6),(7), (11),(12),(14),(15),(18),(20),(21),(22),(26),(27),(28).

The differences in parameters in the preset study may be due to cultural differences, ethnic or genetic variations ,and environmental or geographical change. Changes may occur in the tracheal dimensions like tracheabronchomegaly or tracheomalacia where there is widening of trachea or in tracheobonchopathia where there is generalised narrowing of trachea. So, the knowledge of these parameters on human trachea is very useful in such conditions as well as in conduction of endotracheal intubation in both diagnostic and therapeutic applications.

Limitation(s)

The present study does not include different age groups and sex on which the authors are still working to carry forward this study.

Conclusion

There is wide variation in the dimensions of human trachea in same age group as well as in different age groups. The mean length of trachea was 105.25 mm, mean subcarinal angle was 77.45^o and mean of inter-tracheal ring distance was 1.12 mm in the present study. The study of these morphometric variations is of profound clinical importance as it may help the clinicians to understand the aetiology of several pulmonary diseases and the surgeons to deal with resection and reconstruction of the tracheobronchial tree. Knowledge of length and diameter of trachea also helps the clinicians in choosing the proper size of tracheostomy tube in emergency situations and in proper selection of endotracheal tube. Accurate anatomical knowledge of the variations is essential for knowing pathophysiology and management of different airway disorders.

DOI and Others

DOI: 10.7860/JCDR/2022/55145.16574

Date of Submission: Jan 22, 2022
Date of Peer Review: Feb 19, 2022
Date of Acceptance: May 03, 2022
Date of Publishing: Jul 01, 2022

AUTHOR DECLARATION:
• Financial or Other Competing Interests: None
• Was Ethics Committee Approval obtained for this study? No
• Was informed consent obtained from the subjects involved in the study? No
• For any images presented appropriate consent has been obtained from the subjects. No

PLAGIARISM CHECKING METHODS:
• Plagiarism X-checker: Jan 25, 2022
• Manual Googling: May 03, 2022
• iThenticate Software: May 28, 2022 (7%)

ETYMOLOGY: Author Origin