Variations of Tracheal Cartilages
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The trachea, located in the superior mediastinum, is the proximal part of the tracheobronchial tree (Anne M Gilory 2012). It is approximately 5 inches long and 1 inch in diameter; courses inferiorly anterior to esophagus and posterior to aortic arch (John T Hansen et al. 2005). The trachea extends from the lower border of the cricoid cartilage opposite C6 vertebra up to the upper border of T5 vertebra where it ends by dividing into right and left principal bronchi supplying the right and left lungs respectively (S Nandi,2005). It is a passageway for air between the lungs and the external environment (Anne M Gilory 2012). Anatomical variations occur throughout the human body, and it refers to a structure that is contrasting to the ‘common. There are many variation found in trachea but some common variation are width and dimension of trachea between men and women, variation in size of complete tracheal ring and variation in diameter of the trachea. The aim of this report is to discuss anatomical variation of trachea and its clinical impact on human.
Complete tracheal rings are a rare congenital deformity, which occurs in the hyaline cartilage rings of the trachea and results in a narrowing of the tracheal opening. A normal tracheal ring consists of the cartilage in a “C” shape and a softer posterior membrane made of muscle to complete the ring, in a complete tracheal ring however, the cartilage is what makes up the entire ring thereby forming a narrower “O” shape. Complete tracheal ring sufferers can present various symptoms including noisy breathing, recurring pneumonias, wheezing, retractions, wet sounding biphasic noise, cyanosis, apnoea, and chest congestion (Kay 2014). Proper diagnosis and characterisation of complete tracheal rings requires patients to undergo a microlaryngoscopy as well as a bronchoscopy, these tests allow physicians to understand the degree and length of the narrowing of the trachea. Treatment of complete tracheal rings can be determined after diagnosis and is dependent on the condition of the patient and the severity of the narrowing of the trachea. In over 80 per cent of complete tracheal ring cases, surgery in the form of tracheal resection or slide tracheoplasty is required (Sahoo, Karnak, Gildea and Mehta. 2007). Milder forms of complete tracheal rings can be monitored through regular doctor visits and may not require any surgical intervention at all.
The width and dimensions of the trachea are the most common variations found in males and females. A recent study (Jay et al. 1996, pp. 861-864) presented research data, which showed that the width of the trachea is wider in males than females. The study among 38 men and 32 women aged between (13-82 years) showed that average tracheal width for men was 20.9mm ± 0.32 (SD) mm and 16.9 mm ± 0.25 (SD) mm for women (Jay et al. 1996, pp 861-864). This study also stated that there was no statistically significant relationship between tracheal size and age, weight and height but there is a significant difference in gender and can only be seen until late adolescence (Ringgold & Charles 1986, pp 251). The tracheal width for men was significantly wider than women by (P value < 0.005) (Jay et al. 1996). In addition, tracheal dimension was another type of variation found in the men and women. The inner diameter of the cricoid with mucous membrane in situ in women is 11.6 mm (range, 8.9-17.0mm) and 15.0mm (range, 11.0-25mm) in men (Randestad et al. 2000). (Jay et al. 1996) also state that the average tracheal diameter for males was 22 mm (range = 15-27 mm) and 17 mm (range = 13-25 mm) for females. The research show there is variation in size and diameter of male and female trachea but there are no any medical issues found.
The trachea is a vital part of the respiratory system and a normal adult trachea is 120mm long and 25mm in diameter (Saladin 2007). Variations in the diameter of the trachea can cause respiratory problems but also problems during procedures such as transplantation, stenting, intubation and endoscopic (Randestand,Lindholm & Fabian 2000). It has been found that the size of the cricoid ring can range from 11mm-24mm depending on the sex of the person (Montner, Miller & Calboun 1984). Although height, weight and age affect the rate of flow through the trachea, these factors have no correlation to the diameter of the trachea. As mentioned above, the rate of flow through the trachea is affected by the diameter as it has the smallest cross sectional area with the greatest resistance influencing the peak expiratory flow rate (PEFR) (Montner, Miller & Calboun 1984). Through the experiments done by Montner, Miller & Calboun (1984) it was found that variation in diameter to the 3rd tracheal ring caused the largest variation to the PEFR. The trachea is often used to assist in the operation however; there are not many surgeries that reduce the size of the trachea, as there always will be slight variances between different people.
The variation of tracheal and tracheal cartilage is extremely important to understand because it may help the clinicians to understand the etiology of various pulmonary diseases (Nepal med Coll J 2010). It is essential to understand variation in length, width and diameter of trachea by clinicians during transplantation of larynx because helps surgeons to deal with resection and reconstruction of the tracheobronchial tree (Randestad et al 2000). The accurate an anatomical knowledge of variation in size, shape and position of tracheal structure is important when incubation, stenting, endoscopy and transplantation are to be performed (Randestad et al 2000). It also helps medical students to study pulmonary physiology, anesthesiology and while carryout endotracheal intubation and bronchoscopy procedures with skill and perfection (Nepal med Coll J 2010).
Therefore in conclusion, like many other structures within the human body tracheal cartilages have anatomical variations. Investigating the variations it was found, there were common and asymptomatic differences of the tracheal rings like the rings sizes and the differences between men and women’s trachea rings. In addition there were more complex variations like complete tracheal rings that, while not necessarily fatal, it still required proper diagnosis to understand the degree of variation.
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