Something's missing in the chest

Abstract

A 44-year old man presented with symptoms of a productive cough, night sweats and worsening breathlessness on exertion. This was associated with intermittent episodes of left-sided chest pain over several years, together with recurrent chest infections. He was a smoker of at least 10-15 pack years. No haemoptysis or significant weight loss was reported.On clinical examination, the findings were grossly normal. Spirometry revealed a mild obstructive function but no overwhelming evidence to support a diagnosis of bronchial asthma. The patient's inflammatory markers were normal. Microbiology cultures were negative for infective aetiology, including tuberculosis. What did the chest radiograph (Figure 1) show?The chest radiograph illustrated reduced volume of the right hemithorax with compensatory hyperinflation of the left lung. The left pulmonary artery was enlarged. Even when allowing for the slight rotational asymmetry, the right hilum was poorly identified. There was a generalised increase in vascular markings in the right lung, resulting in a hyperlucent left hemithorax. There was shift of the mediastinum to the right side.The differential diagnosis at this stage for a unilateral hyperlucent lung could be categorised by various aetiologies:(1) increased pulmonary air space with decreased blood flow -large airway obstruction with air trapping or endobronchial obstruction -small airway obstruction such as Swyer-JamesMacleod syndrome -pneumothorax in a supine patient;(2) pulmonary vascular cause such as pulmonary artery agenesis, congenital lobar emphysema or central pulmonary embolism; (3) poor radiographic technique; (4) overlying chest wall defect. DiagnosisA definitive diagnosis at this stage was not forthcoming, hence the patient was referred to the lung multidisciplinary meeting where the resulting decision was to perform a staging CT scan of the thorax to help elucidate the cause. What did the CT (Figure 2