Congenital malformations - Trachea
Dr Sarath Ranganathan, Royal Children's Hospital, Melbourne
Introduction: Congenital tracheal malformations may be either intrinsic to the trachea itself or a consequence of external compression of the airway. While congenital tracheal malformations are by definition present at birth, they may only cause symptoms far later in life. The commonest symptom is stridor which is classically biphasic. Other airway-related symptoms (e.g., wheezing, cough, pneumonia, croup) may be present as may be a history of poor feeding and failure to thrive. A history of frequent neck hyperextension is common as the child tries to maximally open the airway.
Tracheal Embryology: The trachea begins its development during the 4th week of the embryological period as an outpouching of the ventral wall of the foregut (respiratory diverticulum). The endodermal lining of the pouch gives rise to the epithelial lining of the trachea. The cartilaginous and muscular components of the trachea are derived from the surrounding splanchnic mesoderm. The pouch elongates in the caudal direction and soon becomes separated from the foregut by the oesophagotracheal septum. The ventral portion forms the trachea and lung buds, while the dorsal portion forms the oesophagus.
Tracheal Agenesis and Atresia: Tracheal agenesis and atresia are almost uniformly fatal. Those affected newborns survive only if an alternate pathway for ventilation (eg, a patent broncho-oesophageal fistula) exists.
Tracheal Webs and Stenosis: A tracheal web consists of a thin layer of tissue that usually narrows but does not completely obstruct the tracheal lumen. In contrast to tracheal stenosis, no deformity or abnormality of the underlying cartilage exists. In tracheal stenosis a single tracheal ring, multiple rings, or even the entire length of the trachea may be involved with extension into the bronchi. While affected patients may be symptomatic at birth, symptoms may be delayed several months until the airway lumen is compromised further by exacerbation of an upper respiratory tract infection. Abnormalities associated with tracheal stenosis include vascular slings (e.g. a pulmonary artery sling where the left pulmonary artery passes between the trachea and oesophagus, resulting in distal tracheal and right main bronchus compression), tracheo-oesophageal fistulas, pulmonary hypoplasia, and trisomy 21.
Tracheomalacia: In tracheomalacia, the supporting structure of the trachea is compliant, resulting from weakness of the tracheal walls. In addition, the posterior or membranous portion of the trachea, which does not add support to the trachea, may be wider than normal. When respiratory effort is increased the membranous posterior wall advances anteriorly, where it may approach or even appose the cartilaginous anterior tracheal wall, thus markedly reducing the calibre of the airway lumen. Primary tracheomalacia is a congenital disorder of the tracheal rings and is relatively rare. On the other hand, secondary tracheomalacia is an acquired disorder in which cartilage weakness results from extrinsic vascular compression, mechanical ventilation or in association with tracheo-oesophageal fistulae.
Tracheo-oesophageal fistulas: Several types of tracheo-oesophageal fistulas (TOFs) exist, which may or may not be associated with oesophageal atresia. The most common form (85%) is proximal oesophageal atresia with a distal TOF, while the next most common type (4%) is the H-type TOF without oesophageal atresia, in which the intact trachea and oesophagus have a connecting tract between them (forming an H shape). Other types include proximal oesophageal atresia with a proximal and distal (i.e., double) TOF (2%) and proximal oesophageal atresia with a proximal TOF (1%). The remaining 8% of cases are isolated oesophageal atresia without a TOF. TOFs are associated with trisomy 18, trisomy 21, and the VATER (also known as VACTERL) syndrome: vertebral, anal, cardiac, TOF,, renal, and limb abnormalities.
Other Congenital Tracheal Malformations: A tracheal bronchus represents an abnormal tracheal bifurcation above the level of the carina. Incidence is estimated at 3-4%, with right side bronchi being more common.. Tracheal cysts develop from evaginations of tracheal buds and may develop anywhere along the trachea.
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