Upper Airway Structure, Function and Disease s1

CONGENITAL UPPER AIRWAY DISORDERS IN CHILDREN

Robert Berkowitz Royal Children's Hospital, Melbourne, Australia

Congenital upper airway abnormalities usually present as upper airway obstruction in infancy characterised by stridor, respiratory distress and failure to thrive. Poor weight gain is a hallmark of severity and occurs because of the respiratory effort required to overcome obstruction. There are a number features of congenital upper airway abnormalities causing obstruction which are distinctive in infants, compared with older children and adults. These include; - importance of both functional and structural causes - airway abnormality may be isolated or be part of a multi-system disorder - children are obligate nose breathers in the first three months of life and therefore obstruction at the level of the nose is as clinically significant as obstruction elsewhere in the airway Congenital upper airway abnormalities may be classified according to the site of the lesion and subclassified based on whether the abnormality is structural or functional. Assessment by awake flexible laryngoscopy is often the only investigation required(1). The causes can be classified as;

-Nose/nasopharynx Nasal obstruction may occur due to inflammation of the nasal mucosa, septal deformity occurring due to traumatic delivery, or bony obstruction at the level of either the piriform aperture, mid-nose due to medial displacement of the lateral nasal wall, and choanal atresia(2). Nasal masses include naso-cranial anomalies, dermoids, haemangiomas and teratomas.

-Oral/oropharynx Oropharyngeal obstruction is most commonly due to prolapse of the tongue base (glossoptosis) which is often associated with micrognathia. This combination with cleft palate is the Pierre Robin sequence. Enlargement of the tongue is seen in Down's syndrome and Beckwith Weideman syndrome. Oral masses, particularly involving the floor of mouth, include haemangiomas and cystic hygromas.

-Supraglottis Laryngomalacia is the commonest cause of stridor in infants and is due to supraglottic inspiratory collapse. It occurs due to an imbalance between the negative inspiratory pressure which collapses the airway, and supraglottic neuromuscular control which supports the airway. Layngomalacia resolves by two years of age(3). Congenital cysts include vallecular cysts, saccular cysts and laryngoceles(4)

-Glottis Bilateral vocal cord paralysis almost exclusively involves the laryngeal abductors, and rather than being paralysed, the abductors display a loss of respiratory modulation. It may occur due to a structural CNS abnormality, (especially Arnold-Chiari malformation), generalised neuromuscular disorder, birth trauma, or be idiopathic(5). Congenital glottic webs are rare, and are thought to represent a forme fruste of laryngeal atresia. -Subglottis Subglottic stenosis is generally acquired, and occurs following longterm endotracheal intubation. It is seen in premature neonates with lung disease who have required longterm ventilatory support, but this condition now appears to be decreasing due to improved neonatal care(6,7,8). Mucus retention cysts may develop following only brief intubation (9). Subglottic haemangiomas are benign congenital vascular tumours which enlarge with age before regressing spontaneously. Symptoms develop from 6 weeks of age.

-Trachea Tracheomalacia, weakening and collapse of the trachea, may occur due to extrinsic pressure due to a cardiovascular abnormality (most commonly from the inominate artery) or a mediastinal mass, it may be related to a focal abnormality such as a tracheo- esophageal fistula, or be a widespread primary abnormality. Tracheal stenosis may be characterised by an area of narrowing, or be due to complete tracheal rings with absence of the membranous trachea.

References:

1. Berkowitz RG. Neonatal upper airway assessment by awake flexible laryngoscopy. Ann Otol Rhinol Laryngol 1998;107:75-80 2. Brown OE, Pownell P, Manning SC. Choanal atresia: a new anatomic classification and clinical management applications. 3. Cotton RT, Prescott CAJ. Congenital anomalies of the larynx In Practical Pediatric Otolaryngology. Eds Cotton RT, Myer CM III, Lippincott-Raven Pub, Philadelphia, 1999 p497-514 4. Gutierrez JP, Berkowitz RG, Robertson CF. Vallecular cysts in newborns and young infants. Ped. Pulm 1999;27:282-5 5. Berkowitz RG. Vocal cord paralysis. In Practical Pediatric Otolaryngology Eds Cotton RT, Myer CM III, Lippincott-Raven Pub, Philadelphia 1999, p613-24. 6. Cotton RT, Seid AB. Management of the extubation problem in the premature child: Anterior cricoid split as an alternative to tracheostomy. Ann Otol 1980;89:508-11 7. Cotton RT, Myer CM, Bratcher GO, Fitten CM. Anterior cricoid split 1977-87. Arch Otolaryngol Head Neck Surg 1988;114:1300-2 8. Cotton RT, Evans JNG. Laryngotracheal reconstruction in children: A five year follow- up. Ann Otol Rhinol Laryngol 1981;99:515-20 9. Smith SP, Berkowitz RG, Phelan PD. Acquired subglottic cysts in infancy. Arch Otolaryngol Head Neck Surg 1994;120:921-4