Chapter 2 Congenital Abnormalities of the Thorax
Several congenital abnormalities of the thorax have been described, but most are rare. Classification of these anomalies is difficult because the embryologic basis often is not clearly understood. A classification based on thoracic anatomic structures uses the categories of trachea, bronchi, lung, and pulmonary vasculature. Congenital abnormalities involving the mediastinum are discussed in Chapter 15, and airway anomalies are discussed in Chapter 13.
Box 2-1 Congenital Abnormalities of the Thorax
TRACHEA
BRONCHI
Bronchial Atresia
This anomaly consists of atresia of a lobar or segmental bronchus with obliteration of the lumen and preservation of distal structures. The most common site is the left upper lobe, particularly the apical posterior segment. The right middle and upper lobes are less common sites. Mucus secreted within the airways distal to the atretic segment cannot pass the stenosis and accumulates as a mucous plug or mucocele. Collateral air drift keeps the lobe or segment inflated, and it becomes hyperinflated as a result of expiratory air trapping. The chest radiograph shows an area of hyperlucency in the affected portion of the lung (Fig. 2-6). The mucocele appears as an ovoid or branching structure at the hilar level. CT demonstrates the mucoid impaction at the site of obstruction, which is associated with lobar or segmental hyperinflation (Fig. 2-7). There may be an accompanying shift of the mediastinum and compression of the surrounding lung.
Congenital Bronchiectasis
Congenital bronchiectasis (i.e., Williams-Campbell syndrome) is rare, and its existence is controversial. It results from an intrinsic abnormality of cartilage. The cartilaginous deficiency occurs within the fourth- to sixth-order bronchi and is manifested by cystic bronchiectasis and pulmonary hyperinflation (Fig. 2-8). Bronchiectasis, which is acquired and caused by chronic infection, may occur early in life as a result of other congenital, developmental, or genetic disorders. These conditions are listed in Box 2-2 (see Chapter 13).
LUNGS
Pulmonary Agenesis and Hypoplasia
Agenesis, aplasia, and hypoplasia more frequently involve the right lung. In agenesis, the radiograph shows complete absence of an aerated lung in one hemithorax, with pronounced reduction in the volume of that hemithorax and associated shift of the mediastinum to the affected side (Fig. 2-9). There is usually pronounced compensatory overinflation of the contralateral normal lung. Pulmonary hypoplasia has similar findings because of volume reduction; however, there is a small lung on the affected side. In some cases, it may be difficult on standard radiographs to distinguish severe pulmonary hypoplasia from aplasia or agenesis. In such instances, CT may help to identify the absence or presence of the ipsilateral pulmonary artery and bronchus or the presence of a rudimentary bronchus in pulmonary aplasia. CT also can demonstrate rudimentary pulmonary tissue in the base of the hemithorax in patients with severe pulmonary hypoplasia and show a patent bronchus and accompanying pulmonary artery (Fig. 2-10).