Congenital lobar emphysema (CLE)

Findings

A histologic view of the lung parenchyma affected by CLE revealed the characteristically enlarged and overdistended alveoli and rupturing of the interalveolar septae due to the overdistension. Unlike other postinflammatory or destructive causes of emphysematous change, regions of fibrosis are absent. Chest radiographs (Figure 1) and axial CT (Figure 2) examinations obtained at 24 hours were compared with follow-up examinations studies acquired at 48 hours of life. The initial examinations revealed partial consolidation in the superior left lobe (Figure 3). Newborns with CLE have the potential to exhibit rapid evolution of imaging findings, as was exemplified by repeat imaging at 48 hours that revealed a partial resolution of the consolidation. On CT, the bronchovascular tissue in this region is proportionally less than in the remainder of the lungs, and some of the left lung vessels were shown to be convex anteriorly (white arrows) indicating increasing volume of the hyperlucent region when compared to the prior CT (Figure 4). This process exemplifies the expansion of lung affected by CLE, the resorption of residual fluid in this location and the aeration of the patient's atelectasis.

Discussion

Congenital lobar emphysema is a rare neonatal respiratory tract pathology that may cause an emergent clinical picture requiring urgent surgical intervention.¹ Congenital lobar emphysema is characterized by an overinflation of the pulmonary lobe, which is usually diagnosed based on radiological findings. The term emphysema may be misleading, as some children with apparent CLE have reversible overinflation, without the classic alveolar septal rupture (Figure 1) implied by the diagnosis of emphysema.

Congenital lobar emphysema usually presents at birth (33%) or within the first month of life (50%) with moderate respiratory distress. Presentation after 6 months of age is uncommon (5%).^2,3 The exact cause of CLE is often difficult to determine, with no apparent cause found in 50% of cases. Many cases seem to be due to obstruction of a bronchus by a ball-valve mechanism.¹ The most common cause is a congenital cartilage defect, ranging from hypoplastic and flaccid tissue to its complete absence, accounting for 25% of cases. The other 25% are constituted by other causes of bronchial obstruction, such as redundant mucosal folds or septa, mucous plugging, anomalous cardiopulmonary vasculature, and, rarely, intrathoracic masses.³

Congenital lobar emphysema is more common in males than in females (3:1). The left upper lobe is most often involved, followed by the right middle lobe, then the right upper lobe. The majority of infants present with respiratory distress during the first few days of life and progress as the emphysematous lobe gradually enlarges. Cyanosis is the second most common presentation. It may also rarely present as recurrent attacks of respiratory embarrassment or pulmonary infection in older children.²

A plain chest radiograph is the initial step of radiologic evaluation in a patient with respiratory distress. The early images may be confusing and may lead to a spurious diagnosis of cystic adenomatoid malformation or of other pulmonary masses, as the emphysematous lobe is frequently filled with amniotic fluid that has not yet cleared. This may have a masslike or consolidated appearance.⁴ Once the fluid clears, it may appear as a large, space-occupying emphysematous lobe with indistinct lung and vessel markings. This frequently results in atelectasis in the adjacent pulmonary lobe. There is also widening of the rib spaces, flattening of the ipsilateral diaphragm, and a mediastinal shift to the contralateral side. The key point is that CLE can have different appearances at different times as it evolves (Figure 2).¹ Additional studies that may prove useful in diagnosis and management include a lateral decubitus chest film, a CT scan (Figures 3 and 4), fluoroscopy, and a ventilation-perfusion scan.⁵

Differential diagnostic considerations vary based on the time of imaging and include pneumothorax, pneumatocele, atelectasis, or hypoplasia of the lung with hyperinflation of the contralateral lung, diaphragmatic hernia, and congenital cystic adenomatoid malformation.² A CT of the chest may show bronchial obstruction as the cause of the overinflated lobe, but it is not always needed to make the diagnosis. Bronchoscopy in the diagnosis of CLE is controversial, although it should be used to exclude foreign body aspiration in suspected cases. Total lobectomy of the involved lobe is the standard treatment in patients with CLE and severe symptoms. For those with mild symptoms and minimal hyperaeration, conservative management and follow-up (with possible elective lobectomy if symptoms progress) is the appropriate management.⁵

CONCLUSION

The initial imaging findings of CLE may be nonspecific and can be confused with other entities affecting newborn infants. The imaging appearance of CLE may evolve rapidly during the first days following birth and these rapid changes should provide important clues to the underlying disorder. The appropriate imaging work-up can make the determination of the underlying process much easier and can aid greatly in arriving at the correct diagnosis.

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5. Wansaicheong GK, Ong CL. Congenital lobar emphysema: Antenatal diagnosis and follow up. Australas Radiol.1999;43:243-245.