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Congenital Disorders of the Lung
Pulmonary Agenesis and Aplasia
Etiology and Pathology
Pulmonary agenesis differs from hypoplasia in that agenesis entails the complete absence of a lung. Agenesis differs from aplasia by the absence of a bronchial stump or carina that is seen in aplasia. Bilateral pulmonary agenesis is incompatible with life, manifesting as severe respiratory distress and failure. Pulmonary agenesis is thought to be an autosomal recessive trait, with an estimated incidence of 1 in 10,000-15,000 births.
Clinical Manifestations and Prognosis
Unilateral agenesis or hypoplasia can have few symptoms and nonspecific findings, resulting in only 33% of the cases being diagnosed while the patient is living. Symptoms tend to be associated with central airway complications of compression, stenosis, and/or tracheobronchomalacia. In patients in whom the right lung is absent, the aorta can compress the trachea and lead to symptoms of central airway compression. Right lung agenesis has a higher morbidity and mortality than left lung agenesis. Pulmonary agenesis is often seen in association with other congenital anomalies such as the VACTERL sequence ( v ertebral anomalies, a nal atresia, c ongenital heart disease, t racheoesophageal fistula, r enal anomalies, and l imb anomalies), ipsilateral facial and skeletal malformations, and central nervous system and cardiac malformations. Compensatory growth of the remaining lung allows improved gas exchange, but the mediastinal shift can lead to scoliosis and airway compression. Scoliosis can result from unequal thoracic growth.
Diagnosis and Treatment
Chest radiographic findings of unilateral lung or lobar collapse with a shift of mediastinal structures toward the affected side can prompt referral for suspected foreign body aspiration, mucous plug occlusion, or other bronchial mass lesions. The diagnosis requires a high index of suspicion to avoid the unnecessary risks of bronchoscopy, including potential perforation of the rudimentary bronchus. CT of the chest is diagnostic, although the diagnosis may be suggested by chronic changes in the contralateral aspect of the chest wall and lung expansion on chest radiographs. Because pulmonary agenesis can be associated with a wide variety of congenital lesions, whole body MRI can be useful to determine whether other systems (e.g., cardiac, gastrointestinal) are affected. Conservative treatment is usually recommended, although surgery has offered benefit in selected cases.
Bibliography
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Dillman JR, Sanchez R, Ladino-Torres MF, et. al.: Expanding upon the unilateral hyperlucent hemithorax in children. Radiographics 2011; 31: pp. 723-741.
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Kim K, Min KH, Park SJ, et. al.: Right pulmonary agenesis in a 12-year-old girl. Am J Respir Crit Care Med 2011; 184: pp. 742-743.
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Pierron C, Sigal-Cinqualbre A, Lambert V, et. al.: Left pulmonary artery sling with right lung aplasia. J Pediatr Surg 2011; 46: pp. 2190-2194.
Pulmonary Hypoplasia
Etiology and Pathology
Pulmonary hypoplasia involves a decrease in both the number of alveoli and the number of airway generations. The hypoplasia may be bilateral in the setting of bilateral lung constraint, as in oligohydramnios or thoracic dystrophy. Pulmonary hypoplasia is usually secondary to other intrauterine disorders that produce an impairment of normal lung development (see Chapter 122 ). Conditions such as deformities of the thoracic spine and rib cage (thoracic dystrophy), pleural effusions with fetal hydrops, congenital pulmonary airway malformation, and congenital diaphragmatic hernia physically constrain the developing lung. Any condition that produces oligohydramnios (fetal renal insufficiency or prolonged premature rupture of membranes) can also lead to diminished lung growth. In these conditions, airway and arterial branching are inhibited, thereby limiting the capillary surface area. Large unilateral lesions, such as congenital diaphragmatic hernia or pulmonary airway malformation, can displace the mediastinum and thereby produce a contralateral hypoplasia, although usually not as severe as that seen on the ipsilateral side.
Clinical Manifestations
Pulmonary hypoplasia is usually recognized in the newborn period, owing to either the respiratory insufficiency or the presentation of persistent pulmonary hypertension (see Chapter 122.7 ). Later presentation (tachypnea) with stress or respiratory viral infection can be seen in infants with mild pulmonary hypoplasia.
Diagnosis and Treatment
A variety of imaging techniques, including MRI and ultrasound, with estimation of oligohydramnios, can be helpful to identify hypoplasia but not to predict pulmonary function. Mechanical ventilation and oxygen may be required to support gas exchange. Specific therapy to control associated pulmonary hypertension, such as inhaled nitric oxide, may be useful. In cases of severe hypoplasia, the limited capacity of the lung for gas exchange may be inadequate to sustain life. Extracorporeal membrane oxygenation can provide gas exchange for a critical period of time and permit survival. Rib-expanding devices (vertically expansible prosthetic titanium ribs) can improve the survival of patients with thoracic dystrophies (see Chapter 720 ).
Bibliography
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Parikh DH, Rasiah SV: Congenital lung lesions: postnatal management and outcome. Semin Pediatr Surg 2015; 24: pp. 160-167.
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Puligandla PS, Laberge JM: Congenital lung lesions. Clin Perinatol 2012; 39: pp. 331-347.
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Vergani P: Prenatal diagnosis of pulmonary hypoplasia. Curr Opin Obstet Gynecol 2012; 24: pp. 89-94.
Congenital Cystic Malformation (Congenital Pulmonary Airway Malformation)
Pathology
Congenital pulmonary airway malformation (CPAM) , formerly known as cystic adenomatoid malformation, consists of hamartomatous or dysplastic lung tissue mixed with more normal lung, generally confined to 1 lobe. This congenital pulmonary disorder occurs in approximately 1-4 in 100,000 births. Prenatal ultrasonographic findings are classified as macrocystic (single or multiple cysts >5 mm) or microcystic (echogenic cysts <5 mm). Five histologic patterns have been described. Type 0 (acinar dysplasia) is least common (<3%) and consists of microcystic disease throughout the lungs. The prognosis is poorest for this type, and infants die at birth. Type 1 (60%) is macrocystic and consists of a single or several large (>2 cm in diameter) cysts lined with ciliated pseudostratified epithelium; the lesion is localized involving only a part of 1 lobe. One third of cases have mucus-secreting cells. Presentation is in utero or in the newborn period. Cartilage is rarely seen in the wall of the cyst. This type has a good prognosis for survival. Type 2 (20%) is microcystic and consists of multiple small cysts with histology similar to that of the type 1 lesion. Type 2 is associated with other serious congenital anomalies (renal, cardiac, diaphragmatic hernia) and carries a poor prognosis. Type 3 (<10%) is seen mostly in males; the lesion is a mixture of microcysts and solid tissue with bronchiole-like structures lined with cuboidal ciliated epithelium and separated by areas of nonciliated cuboidal epithelium. The prognosis for this type, like type 0, is poor. Type 4 (10%) is commonly macrocystic and lacks mucus cells. It is associated with malignancy (pleuropulmonary blastoma) and can present either in childhood or in asymptomatic adults.
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