Discussion
The association between congenital heart defects and CLE is well known, and large left-to-right shunts are commonly associated with CHD. Cough, tachypnea, and respiratory distress in early infancy are the usual clinical presentations in both conditions. As CHD is more prevalent, it is often suspected and diagnosed first. In cases where the entire clinical constellation is attributed to CHD, the presence of CLE is only detected after correction of the CHD. Similar cases have been reported in the past6,7.
The etiology of CLE remains unknown in almost half of the cases. Absent or dysplastic bronchial cartilage is evident in one-fourth of the cases. Internal obstruction or external compression of the lobar bronchus due to various causes is postulated in the remaining cases. These defects cause a ball valve effect and air trapping during expiration with progressive hyperinflation of the affected lung lobe. The hyperinflated lobe may compress the surrounding normal lobes. In patients with severe disease, the hyperinflated lung lobe can herniate to the surrounding lobes as well as to the opposite thoracic cavity with tracheal and mediastinal shifts. This reduces the respiratory reserve and causes a ventilation/perfusion mismatch with resultant hypoxia1,3.
In the embryo, the development of the bronchial cartilage occurs during the 4th to 6th intrauterine weeks. This time coincides with the developmental stage of cardiac chamber septation. Thus, a defect during this stage can affect both the heart and lungs1. CLE is usually secondary to bronchial compression due to aberrant or dilated pulmonary vessels owing to pulmonary hypertension in the presence of a large left-to-right shunt. In this case, CLE may get resolved with the correction of the underlying CHD5,6.
CLE continues to pose a diagnostic dilemma. The initial diagnostic modality is usually a chest X-ray. The affected lung lobe is hyperlucent with atelectasis of the adjacent lung lobes due to compression, and a mediastinal shift can be seen. Though all the features are not evident at an early age, X-ray findings are often misreported as pneumonia owing to the crowding of the surrounding lobes, and the hyperlucency of the affected lobe may get reported as a pneumothorax. A CTscan of the lung is confirmatory and delineates anatomical details. Bronchoscopy may aid the diagnosis when an internal bronchial obstruction is suspected1-4.
Treatment of CLE involves the surgical resection of the affected lobe. Conservative management is proposed for older children with no or minimal symptoms. Infants with persistent distress are ideal candidates for surgery. The surgery is generally well tolerated, with low mortality and favorable outcomes2,8. In the case of concomitant CLE and CHD, there are diverging views regarding the defect to be repaired first, or whether a combined lung and cardiac repair is the ideal approach. An individualized approach has been suggested. CLE often gets corrected with the relaxation of the vascular compression, the repair of the large left-to-right shunt, and the reduction of pulmonary hypertension5,9.
In the present case, the child presented with respiratory distress. During the assessment, clinical suspicion led us to perform 2D echocardiography, which revealed a large VSD with moderate PDA and PAH. The presence of a congenital lung defect was overshadowed by the presence of a large cardiac defect. The symptoms were obviously contributed to the heart defect.The X-ray findings were initially interpreted as being due to pneumonia. As seen in Figure 1 (2 months of age), there is no obvious hyperlucency of the right middle lobe; rather, haziness is evident in the right upper lobe. In contrast, a later X-ray( Figure 2), performed at 7 months of age, clearly demonstrated a large hyperlucent area in the right middle lobe with surrounding lobe crowding and mediastinal shift.In retrospect, we could discern the faint hyperlucency in Figure 1, which was initially missed. We believe that the X-ray chest, being a basic investigation, is often given less attention, particularly when another advanced diagnostic modality has suggested an alternate diagnosis.
CLE is a diagnostic challenge, and the confusion can be further augmented in the presence of an obvious large congenital heart defect. Regular follow-up and a high index of suspicion are necessary for early diagnosis. Lobectomy can lead to dramatic improvement and is generally well tolerated.