© Borgis - New Medicine 4/2004, s. 102-104
Lidia Zawadzka-Glos, Beata Zając, Anna Kaczmarczyk
Laryngeal stridor: structural differences and clinical examination of the child´s larynx
Department of Paediatric Otorhinolaryngology, Medical University of Warsaw, Poland
Head: Prof. Mieczysław Chmielik MD, PhD
Laryngeal stridor is a frequent problem in paediatric laryngology, which results from differences in the anatomical structure of the larynx in the child and that in the adult individual. The knowledge of changes occuring during the development of the child´s larynx determines its adequate evaluation, helps to choose the most appropriate method of examination and to carry out proper assessment of laryngeal abnormalities.
Laryngeal stridor is a frequent problem in paediatric laryngology since the child´s larynx has a different anatomical structure than that of an adult individual.The differences are concerned with the size of particular parts of the larynx and their position to each other.
Cartilage and muscles of the larynx develop from the branchial arches, while the mucosa develops from the foregut. The cricoid cartilage develops earliest, at the end of the first month of gestation; it is the only completely closed ring of cartilage of the larynx. The cricoid cartilage plays an important role in the development of laryngeal stenosis caused by different factors: iatrogenic or inflammatory. Laryngeal stridor in infants and young children is most frequently due to subglottic stenosis at the level of the cricoid cartilage. The thyroid cartilage develops during the second month of gestation from the IVth and Vth branchial arches. The epiglottis probably develops from IVth or IIIrd branchial arches. The laryngotracheal groove continues to deepen and gives rise to the trachea. The larynx descends in the neck at the second half of the intrauterine life. This knowledge is essential to treat prematurely born infants requiring long-term intubation.
The larynx of the infant born at term is located at two cervical vertebrae, higher than in adults. The upper border of the newborn larynx is found at the level of the second cervical vertebra, while the lower border is situated at the level of the third or fourth cervical vertebra. During the child´s growth the larynx descends, and finally, at reaching sexual maturity, it is located at the level from the fourth to seventh cervical vertebrae. The epiglottis is situated more horizontally; it is relatively longer and narrower than in adults, and may be omega- or groove-shaped. The degree of inclination of the epiglottis and its flaccidity or shortening may be a frequent cause of laryngeal stridor associated with laryngomalacia.
The thyrohyoid membrane is very short because the thyroid cartilage is situated just below the hyoid bone. The body of the hyoid bone is opposite the upper incisure of the thyroid cartilage. The laminae of the thyroid cartilage are connected arcuate at an open angle at about 110 degrees. Owing to this structure of the thyroid cartilage, the rima of the glottis is short, and proportion of the membranous and cartilaginous portions are 1:1. According to Holinger, the length of the newborns glottis is 7 mm in its anteroposterior dimension, and it is 4mm in its transverse dimension, near to the posterior commissure. The mucous mem-brane of the larynx is flaccid and incoherently connected with cartilage and muscle. It contains abundant connective tissue with elements of lymphoid tissue. The largest amount of loose connective tissue is found at the subglottic portion and on the posterior wall of the larynx, in arytenoepiglottic folds and on the surface of the epiglottis. The subglottic portion is characteristically sandglass-shaped in children, because of slopping posteriorly to the plate of the cricoid cartilage, as compared to the cylindrically-shaped structure in adult individuals. The subglottic portion is the narrowest part of the larynx, encircled by the closed ring of the cricoid cartilage. According to many authors (Wilson, Fearon, Cotton) the diameter of the subglottic portion in the newborn ranges from 4.5 mm to 5.5 mm. These physical parameters of the subglottic portion and the presence of lymphatic elements in the mucous membrane predispose to an impaired patency of the respiratory tract during infection, which may rapidly produce dyspnoea and stridor.
Not only does the position of the larynx change in relations to the vertebral column but also its shape changes during the child´s growth. The epiglottis, firstly sloped backwards and located horizontally, is subsequently elevated, and its shape changes. The plates of the thyroid cartilage enlarge and are situated at a more acute angle. The anteroposterior diameter of the larynx increases, which leads to the elongation of the vocal folds and the proportion of the membranous and cartilaginous portions changes from 1:1 to 1:3. Gradually, the soft connective tissue connected with mucous membrane regresses. The subglottic portion becomes cylindrically-shaped; according to Freeland, its diameter increases by about 0.5 mm per year reaching the total diameter of 12.5 mm in the child of twelve years of age. Laryngeal stridor is significantly less frequent in older children and adults than in infants and the youngest children due to the changes in the structure of the larynx.
It is necessary to take a careful history and to perform a thorough physical examination to establish the proper diagnosis, to begin adequate diagnostic and treatment procedures. The symptoms of the upper respiratory obstruction vary according to an underlying pathology. Taking a detailed history is essential before proceeding to any further additional investigation.
The following questions are recommended on interviewing the child´s parents/ guardians:.
1. Are the symptoms acute or chronic?
2. Does stridor occur?
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