Pulmonary bullae are air-filled cavities within the lung tissue, larger than 1 cm in diameter, that result from the rupture and merging of alveolar walls under increased intralveolar pressure. When air enters the subpleural space after alveolar rupture, subpleural blebs (blebs) are formed, which are not strictly considered pulmonary bullae.
Etiology and Pathology
Pulmonary bullae are often secondary to inflammatory processes in the small bronchi, such as pneumonia, pulmonary tuberculosis, or emphysema. Inflammatory changes, including edema and narrowing of the small bronchi, can lead to partial airway obstruction and a valve-like mechanism, allowing air to enter but not leave the alveoli. This causes increased intralveolar pressure. Inflammation also damages lung tissue, gradually causing alveolar walls and septa to rupture as intralveolar pressure rises further. The merging of neighboring alveoli forms larger air-filled cavities (bullae). Some pulmonary bullae are caused by congenital genetic abnormalities, while many cases remain of unknown etiology and are classified as idiopathic pulmonary bullae in clinical practice.
Pulmonary bullae may be solitary or multiple. Those secondary to pneumonia or tuberculosis are often solitary, whereas those associated with emphysema are typically multiple and often poorly demarcated from surrounding emphysematous lung tissue. Microscopically, the walls of bullae may consist of flattened alveolar epithelium, or they may only consist of fibrous membranes or fibrous connective tissue.
Clinical Presentation
The clinical manifestations of pulmonary bullae depend on the number, size, and coexistence of other pulmonary diseases. Small and limited pulmonary bullae can be asymptomatic and are often incidentally detected on chest X-rays or CT scans. Patients with large or multiple bullae may experience chest tightness and shortness of breath. A minority of cases present with hemoptysis or chest pain.
Complications
The main complications of pulmonary bullae include spontaneous pneumothorax or spontaneous hemopneumothorax, with secondary infections occurring less frequently.
Spontaneous Pneumothorax
This is the most common complication of pulmonary bullae. Symptoms include sudden-onset chest pain, dyspnea, coughing, and respiratory distress. Physical findings include hyper-resonance on percussion of the affected hemithorax and diminished or absent breath sounds on auscultation. Severe cases may involve tracheal deviation to the contralateral side. Symptom severity depends on the volume of pneumothorax, duration of the condition, and presence of coexisting pulmonary diseases.
Spontaneous Hemopneumothorax
This complication is rare and usually results from rupture of small blood vessels within pleural adhesions during the onset of pneumothorax. In addition to symptoms of pneumothorax, patients may present with dizziness, palpitations, pallor, and other signs of blood loss. Chest X-rays often reveal both air and fluid levels in the pleural cavity. Progressive hemothorax occurs in some cases, requiring emergency surgical intervention.
Secondary Infection
Infected pulmonary bullae become filled with inflammatory material, causing the air cavity to disappear or form an air-fluid level. Patients may exhibit symptoms such as cough, sputum production, fever, and worsening dyspnea.
Diagnosis and Differential Diagnosis
Chest X-ray and CT are the primary diagnostic tools for identifying pulmonary bullae.
Chest X-ray findings include thin-walled air cavities within the lung fields with reduced pulmonary markings or only streak-like shadows within the cavities. Compressively underinflated lung tissue may surround large bullae. CT scans more clearly delineate the number and size of the bullae and identify coexisting pulmonary diseases.
Large pulmonary bullae require differentiation from pneumothorax. Pneumothorax typically presents with acute onset and rapid progression, whereas bullae develop more slowly. Both may show localized radiolucency on chest X-rays, but pneumothorax typically has a darker radiolucent appearance with complete absence of pulmonary markings in the area, and the lung tissue appears compressed toward the hilum, with a curvature opposite to that seen in bullae. Chest CT is an effective diagnostic tool for differentiation. Efforts to confirm the diagnosis with thoracentesis should be approached cautiously in cases where differentiation between giant pulmonary bullae and pneumothorax is challenging, as puncture of the bullae may result in iatrogenic pneumothorax or even tension pneumothorax.
Treatment
Pulmonary bullae represent irreversible lung damage, and no effective pharmacological treatments are currently available. Asymptomatic pulmonary bullae discovered during examinations often do not require intervention.
Surgical Indications
Surgical indications include:
- Pulmonary bullae causing spontaneous pneumothorax or hemopneumothorax.
- Large pulmonary bullae causing significant symptoms due to compression of adjacent lung tissue.
- Recurrent infections of pulmonary bullae.
Surgical Techniques
Most pulmonary bullae can be completely excised via wedge resection during video-assisted thoracoscopic surgery (VATS).
Bullae that cannot be completely excised may be opened, with attention paid to suturing the sites of air leakage and excising redundant bulla walls. The edges of the excised areas are then closed.
Deeply located pulmonary bullae are typically not treated unless they are large or infected.
Small or centrally located bullae near the lung hilum may be managed with ligation or suture techniques if wedge resection is not feasible.
If the affected lobe has little normal lung tissue remaining in addition to the bullae, lobectomy may be performed.
Patients with pulmonary bullae complicated by recurrent pneumothorax are often advised to undergo concomitant pleurodesis during surgery. This promotes pleural adhesions and reduces the likelihood of recurrent spontaneous pneumothorax.