Teaching Case

A 58-year-old man was admitted to first aid for onset of left thoracic pain, dyspnoea and low-grade fever.
His clinical history included a previous diagnosis of bullous emphysema with several giant bullae in the left lung.
Laboratory tests showed a moderate increase of inflammatory parameters.

The chest X-ray showed two well-defined air-fluid levels inside of large emphysematous bubbles in the left lung. An unenhanced CT showed a severe bilateral bullous emphysema with medium-sized bullae in the right lung and several large cavities in the left lung, containing some liquid with air-fluid levels. The walls of the bullae were regular and very thin. The comparison with a previous chest radiograph (Fig. 1c-d) and a CT examination (Fig. 2c-d) performed several months before showed an increase in size of the large bubbles in the left lung and the appearance of fluid inside them. Based on the radiological findings, the minimal symptomatology and evidence of pre-existing emphysematous bubbles without air-fluid levels, a diagnosis of infected emphysematous bulla was suggested. The patient underwent prolonged systemic antibiotic therapy and follow-up. An unenhanced CT performed after four weeks showed considerable reduction of the amount of fluid inside the bulla (Fig. 2e)

The presence of air-fluid levels inside an emphysematous bulla is not a frequent radiological evidence and for this reason it is rarely reported in the literature [1].
Its pathophysiology is not clear yet, however, several theories have been proposed: an insufficient bronchial communication can cause an inadequate drainage of the bulla resulting in a fluid accumulation inside it. The fluid can initially be sterile and can afterwards become infected due to the spread of an infection in the surrounding lung or via haematogenous spread. A bleeding within the bulla or a malignancy are other more rare but possible aetiologic mechanisms [1, 2, 3].
First described in 1947 by Drouet [4], this pathology occurs predominantly in male smokers and shows no predilection of side or age.
The clinical presentation varies from incidental symptomless findings to symptoms of acute lung infection but generally milder signs are identified such as low-grade fever, cough, chest pain and dyspnoea.
The chest radiography shows one or more air-fluid levels inside a radiolucent bulla. CT is the most appropriate imaging modality to determine the exact size and site of the bulla, the amount of fluid and the features of the cavity's walls. These are generally regular and very thin; unlike lung abscess which remains the main differential diagnosis.
The diagnosis relies on the discrepancy between the radiological findings and the presence of a minimal symptomology; especially if there is evidence of pre-existing emphysematous bullae without air-fluid levels [1, 2, 5].
The most common therapeutic approach for this condition is the prolonged administration of systemic antibiotics and follow-up until recovery, which might take up to several weeks.
If the conservative treatment fails, a percutaneous or endoscopical drainage can be considered, while surgical resection is considered a contraindication because of the persistent air leakage due to lung damage [2, 6, 7, 8].