A 29-year-old woman is referred to the clinic with a history of repeated respiratory tract infections. There is no significant travel history and she denies any possibility of foreign body aspiration. On examination, she has coarse crackles in the left lower lung zone. CXR is shown in Fig.. Based on the history and CXR, the next diagnostic step should be

This x-ray shows a cystic opacity in the left lower lobe behind the hea obscuring the left diaphragm but not obscuring the left hea border. These cystic-appearing shadows originate from the left lower lobe bronchus. This picture is consistent either with left lower lobe bronchiectasis or sequestration of the lung. The chest x-ray and clinical history suggest bronchiectasis of the left lower lobe. Bronchograms are not done anymore because of frequent complications and the fact that a CT scan can confirm the diagnosis. Bronchoscopy would not reveal any additional information unless there is a history of foreign body aspiration. Determination of immunoglobulin levels would be helpful in a patient with chronic generalized or multilobar infection or frequent skin infections. The differential diagnosis in this case would include pulmonary sequestration, which could present with a similar radiological picture. A pulmonary sequestration is an abnormal embryonic lung tissue that is segregated from the tracheal bronchial system and does not communicate through normal bronchus. Since the sequestrated lung is cystic, it does not function normally. There are two types of pulmonary sequestration. Intralobar sequestrations, seen most frequently in adults, are located within the visceral pleura and are contained within the lung parenchyma. Extralobar sequestrations, which are located outside the visceral pleura, have their own separate pleural covering. The most common location for intralobar sequestration is the posterior basilar segments of the lower lobe. It is characterized by bronchiectasis with cystic areas containing mucus or mucopurulent material, and is lined with ciliated columnar or cuboidal epithelium. The walls may contain cailage and glands. In the adult, multifocal epithelial changes can occur, and dysplastic or carcinomatotic changes have been repoed within intralobar sequestrations. The most common site of the region of the anomalous aerial supply in pulmonary sequestration is the thoracic aoa, followed by the abdominal aoa and intercostal aeries. Cough and hemoptysis may be the initial symptoms. On plain x-ray, intralobar sequestration appears as a solid or cystic mass located in the lower lobe. Air-fluid levels are seen and may be mistaken for pneumonia, bronchiectasis, or abscess formation. Bronchoscopy reveals no abnormality, and for a definitive diagnosis of sequestration it is impoant to demonstrate the systemic aerial supply. CT scan or aoography can accomplish this. Untreated sequestration has an associated morbidity related to infection, vascular shunting and hemoptysis; thus, resection is the treatment of choice.