An unusual case of unilateral hyperlucent lung

Discussion

CLE is a rare bronchopulmonary malformation characterised by overdistension of the affected lobe due to massive air trapping and accompanying damage to septa leading to compression and displacement of adjacent normal lung tissue [4]. It was first reported by Gross and Lewis in 1954 [8]. It has a prevalence of 4.5 per 100 000, with one third of cases presenting in neonatal period itself and almost all by 6 months of age [9]. First presentation in adulthood is much more uncommon [4, 10].

The aetiology of this abnormality is still unknown, although a variety of causes have been proposed which cause obstruction of the developing airway, leading to ball valve obstruction and air trapping causing emphysema, such as cartilaginous dysplasia of bronchi, vascular anomalies, kinking of the bronchioles, compression by large lymph nodes, mucus plugs, alveolar disease and bronchial stenosis [11, 12]. The most accepted among the theories are bronchial cartilage defects like hypoplasia, flaccid tissue, or absence of cartilage. It occurs twice as often in males as in females [12]. In most cases, the left upper lobe is affected followed by right middle lobe, right upper lobe and lower lobes.

On physical examination, a hyperresonant note on percussion in the afflicted lobe is noted and breath sounds are diminished in that part of the lung. Although rare, wheezing and rhonchus can also be heard.

The most common abnormality seen on spirometry is an obstructive pattern, although it can be normal in mild or asymptomatic cases [10]. Fundamental to diagnosis are the radiological features which are markedly increased volume of the affected lobe, depression of the ipsilateral diaphragm, compression of the surrounding lung parenchyma and displacement of mediastinum to contralateral side suggesting over-inflation and air trapping in the affected lobe. Despite the attenuation of vascular markings in the affected lobe, they are well maintained and can be traced to the periphery of the lung. Chest radiography and CT scan are required to establish the diagnosis. Other adjunctive investigations are a ventilation/perfusion scan, which depicts obstructed and delayed ventilation and slightly decreased perfusion of the affected lobe, and magnetic resonance imaging, which can demonstrate any vascular lesion causing external compression [10, 13].

Diagnosis of CLE can pose a challenge for physicians as there are various conditions that can cause unilateral hyperlucent lung associated with air trapping (also known as obstructive hyperinflation). A review of the literature indicates that some patients were erroneously diagnosed with pneumothorax initially and therefore a careful reading of the radiograph is warranted [14]. A unilateral hyperlucent radiograph can itself be due to a wide variety of reasons and a structured approach can help us to narrow the list of differentials. First and foremost, we must look for the technical quality and rotation of film as it can falsely lead to hyperlucent lung on the side to which the patient is rotated. A systematic look into the details of the radiograph, moving from outside to inside can help us in localising the anatomical site of the abnormality, a summary of which is detailed in table 1.

CLE is known to be associated with congenital heart diseases in about 20% cases. Most common cardiac anomalies are left to right shunts (mainly ventricular septal defects), tetralogy of Fallot, and patent ductus arteriosus. Hence, two-dimensional echocardiography is an essential component in baseline evaluation of CLE patients [15, 16]. A strong suspicion, detailed history, chest CT and bronchoscopy are required to clinch the diagnosis and rule out the resembling diseases.

The treatment of choice for CLE depends on severity of disease [16]. The medical management of the disease includes inhaled bronchodilators and surgical treatment usually involves lobectomy [4, 6, 17]. Recently nonsurgical approaches such as endobronchial valve placement have been attempted in a few cases with promising results and this appears to be a potential future option with a less invasive approach [7]. Fierro et al. [18] performed a retrospective study on six infants to determine if surgical removal of the lobe would improve pulmonary function by inserting a balloon catheter in the affected lobe with bedside bronchoscopy. They postulated that temporary balloon occlusion of the lobe can assist in decision making for a lobectomy in symptomatic infants by monitoring oxygenation, gas exchange and radiological parameters after the occlusion [18].

Similar results were seen when surgical and medical management were compared in a long-term follow-up study of CLE patients [16]. Hence, a severely symptomatic patient or progression of disease should be managed with surgical intervention whereas conservative management can be tried with close follow-up for mild or asymptomatic disease [16, 19, 20].