© 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?
3. What is the character of the stridor? (inspiratory, expiratory, inspiratory-expiratory)
4. Is the stridor related to the the child´s body position?
5. Is the child´s voice normal? Has it become hoarse? Weak? Has there been a loss of voice?
6. Does the stridor occur on effort/ exertion or it is also present at rest?
7. Has there been any dysphagia or any choking or cough episodes on feeding?
8. Has the child ever been intubated?
9. Has the child ever undergone any surgical procedures on the neck or chest?
10. Has gastro-oesophageal reflux been recognized?
Laryngeal stridor is always associated with varying severity of dyspnoea which may occur on exertion/effort (on feeding or crying in infants) or at rest. Depending on the localization of stenosis, dyspnoea may be inspiratory or biphasic: on inspiration and expiration. Inspiratory dyspnoea occurs when the glottis, epiglottic or subglottic portions are stenosed. In a significantly stenosed subglottic portion, inspiratory-expiratory dyspnoea with a prevalent inspiratory phase may be noted.
Due to airway stenosis, respiratory resistance increases markedly, and the accessory respiratory muscles are in use. Nasal flaring, suprasternal, supraclavicular and intracostal retractions may be present. Older children develop orthopnoea; they sit up and occasionally lean on their hands. In severe dyspnoea, retraction of the sternum towards the vertebral column, retraction of the epigastric region, and paradoxical movements of the abdominal wall may be seen in newborns, infants and youngest children, in whom chest the walls are flaccid. The skin is pale, with a grayish tint around the mouth; peripheral cyanosis may be observed. Tachypnoea and tachycardia may also occur. Physical examination in presumed respi-ratory stenosis should assess:
1. the patient´s general condition, skin colour, heart rate, respiratory rate, and blood oxygen saturation;
2. the severity and character of dyspnoea (inspiratory, inspiratory-expiratory, expiratory, relating to effort or rest);
3. the character of stridor at rest, on exertion, and in different body positions;
4. the voice;
5. the larynx.
Laryngeal evaluation in children is a special examination because a typical indirect laryngoscopy is possible only in the oldest children. Patient com-pliance is an essential condition to perform indirect laryngoscopy, thus the indirect laryngoscopy is not used in newborns, infants and young children. The recom-mended technique of the laryngeal examination in children is direct laryngoscopy (directoscopy) using a rigid endoscopic tube or the Kleinsaser kit. Direct laryngoscopy should be preformed by an experienced laryngologist under local or short-acting general anesthesia. Particular levels of the larynx, i.e. the epiglottis, glottis and subglottic portion are evaluated on directoscopy. Mild general anesthesia allows the examiner to assess the mobility of the vocal cords or a characteristic view of inspiratory collapse of the laryngeal cartilages in laryngomalacia. Deep general anesthesia, with controlled ventilation, hinders recognition of congenital laryngomalacia or vocal cord or palsy. The anaesthetist and laryngologist should closely coope-rate; the decision about the type of anesthesia should be made before the directoscopy procedure.
In compliant patients, laryngeal examination will be done by using a flexible endoscope. Fiberoscopy is very useful to evaluate functional disorders of the larynx; it allows assessment of the structure on swallowing, breathing and phonation. A small diameter and low resolution of the fiberoscope show its disadvantage, therefore it may be difficult to assess minute details of the laryngeal mucosa. Fiberoscopy provides a better visualisation of the epiglottis and glottis than of the lower portions of the larynx. It is indicated in patients with burns and trauma to the larynx, and also when typical directoscopy is difficult or impossible to perform, i.e. in a patient with a very short neck (Klippel-Feil syndrome), in ankylosis or other abnormalities of the cervical vertebral column, in micrognathia (Pierre-Robin syndrome), in patients with malocclusion or diseases of the mandibulo-temporal joint, when it is impossible to insert a rigid directoscopy tube into the larynx.
In children with rapid onset of laryngeal stridor, directoscopy is not only a diagnostic tool but has also a treatment goal. The procedure may be used to remove a foreign body, to aspirate retained secretion, to perform mucosal decongestion in acute oedema of the subglottic portion, to remove balloting papilloma.
The symptoms and course of diseases of the larynx in children differ from those in adults. It is essential for the laryngologist to know how the larynx develops to select an appropriate technique to evaluate the structure and to establish the diagnosis. Endoscopy of the respiratory airway is a basic diagnostic procedure in laryngeal stridor. The onset of laryngeal stridor in children may be rapid, so, immediate recognition of the condition and proper treatment may save the patients´ life or improve their health.
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