A lung cavity or pulmonary cavity is an abnormal, thick-walled, air-filled space within the lung. Cavities in the lung can be caused by infections, cancer, autoimmune conditions, trauma, congenital defects, or pulmonary embolism. The most common cause of a single lung cavity is lung cancer. Bacterial, mycobacterial, and fungal infections are common causes of lung cavities. Globally, tuberculosis is likely the most common infectious cause of lung cavities. Less commonly, parasitic infections can cause cavities. Viral infections almost never cause cavities. The terms cavity and cyst are frequently used interchangeably; however, a cavity is thick walled (at least 5 mm), while a cyst is thin walled (4 mm or less). The distinction is important because cystic lesions are unlikely to be cancer, while cavitary lesions are often caused by cancer.
Diagnosis of a lung cavity is made with a chest X-ray or CT scan of the chest, which helps to exclude mimics like lung cysts, emphysema, bullae, and cystic bronchiectasis. Once an imaging diagnosis has been made, a person’s symptoms can be used to further narrow the differential diagnosis. For example, recent onset of fever and productive cough suggest an infection, while a chronic cough, fatigue, and unintentional weight loss suggest cancer or tuberculosis. Symptoms of a lung cavity due to infection can include fever, chills, and cough. Knowing how long someone has had symptoms for or how long a cavity has been present on imaging can also help to narrow down the diagnosis. If symptoms or imaging findings have been present for less than three months, the cause is most likely an acute infection; if they have been present for more than three months, the cause is most likely a chronic infection, cancer, or an autoimmune disease.
The presence of lung cavities is associated with worse outcomes in lung cancer and tuberculosis; however, if a lung cancer develops cavitation after chemotherapy and radiofrequency ablation, that indicates a good response to treatment.
Formal definition In the 2008 Fleischner Society "Glossary of Terms for Thoracic Imaging", a cavity is radiographically defined as “a gas-filled space, seen as a lucency or low-attenuation area, within [a] pulmonary consolidation, a mass, or a nodule”. Pathologically, a cavity is “usually produced by the expulsion or drainage of a necrotic part of the lesion via the bronchial tree.”
Lung cavity mimics The first step in evaluating a suspected lung cavity lesion is to exclude other kinds of abnormal air-filled spaces in the lung, including lung cysts, emphysema, bullae, and cystic bronchiectasis. Lung cysts are the most common mimics of lung cavities. Cavities and cysts are similar in that they are both abnormal, air-containing spaces with clearly defined walls. The difference between cavities and cysts is that cavities are thick walled, while cysts are thin walled. Generally, cavities have walls that are at least 5 mm thick, while cysts have walls that are 4 mm or less, and often less than 2 mm.
The distinction between cysts and cavities is important because the thicker the wall is, the more likely it is to be cancer. Thus, cystic lesions are unlikely to be cancer, while cavitary lesions are often caused by cancer. In a study from 1980 that used chest X-rays to evaluate 65 cases of solitary lung cavities, 0% percent of cavities with walls 1 mm or less were malignant (that is, cancerous), versus 8% of cavities with walls 4 mm or less, 49% of cavities with walls 5 to 15 mm, and 95% of cavities with walls 15 mm or greater. However, a 2007 study that used CT to evaluate lung cavities showed no relationship between wall thickness and the likelihood of malignancy. It did show that malignant cavities are more likely than benign cavities to have an irregular internal wall (49% vs 26%) and have an indentation of the outer wall of the cavity (54% vs 29%).
Areas of emphysema are abnormal, air-filled spaces that usually do not have visible walls, and bullae are very thin walled (<1 mm). Cystic bronchiectasis is irreversible bronchial dilation, which is permanent widening of the bronchioles (small airways) in the lung. It can be distinguished on imaging by a lack of bronchial tapering, meaning that the bronchioles do not get narrower as they travel further into the lung. Cystic bronchiectasis is also associated with an increased bronchoarterial ratio, meaning that the bronchioles are larger than the blood vessels that run alongside them.
Infectious causes Bacterial, mycobacterial, and fungal infections are common causes of lung cavities. Globally, tuberculosis is likely the most common infectious cause of lung cavities. Less commonly, parasitic infections can cause cavities. Viral infections almost never cause lung cavities; in a small study of immunocompromised patients with a lung infection, the presence of a cavity on CT scan essentially ruled out viral infection. In the same study, about one-third of the cavities were caused by a bacterial infection, another third were caused by a mycobacterial infection, and another third were caused by a fungal infection.
Bacterial Bacteria can cause lung cavities in one of two ways; they can either enter the lung through the trachea (windpipe), or they can enter through the bloodstream as septic pulmonary emboli (infected blood clots). Community-acquired pneumonia is an uncommon cause of lung cavities, but cavitary pneumonia is occasionally seen with Streptococcus pneumoniae or Haemophilus influenzae infection. However, since these two species of bacteria are such common causes of pneumonia, they may cause a significant fraction of all cavitary pneumonias. The most common bacterial causes of lung cavities are Streptococcus species and Klebsiella pneumoniae. Less commonly, the bacteria Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter, Escherichia coli, and Legionella can cause cavitation. Nocardia is a bacterium that can cause pulmonary nocardiosis and lung cavities in people who are immunocompromised (have weak immune systems), including organ transplant recipients who are on immunosuppressants, and those with AIDS, lymphoma, or leukemia. Melioidosis, caused by the bacteria Burkholderia pseudomallei, is common in tropical areas, especially Southeast Asia, and is frequently associated with lung cavities.
Pneumonia can lead to the development of a lung abscess, which is a pus-containing necrotic lesion of the lung parenchyma (lung tissue). On CT scan of the chest, a lung abscess appears as an intermediate- or thick-walled cavity with or without an air-fluid level (a flat line separating the air in the cavity from the fluid). An abscess can occur anywhere in the lung. Risk factors for polymicrobial lung abscesses (abscesses caused by multiple species of bacteria) include alcoholism, a history of aspiration (food or water accidentally going down the trachea), poor dentition (bad teeth), older age, diabetes mellitus, drug abuse, and artificial ventilation. Polymicrobial lung abscesses are usually due to aspiration and are located in the posterior segments of the upper lobes or superior segments of the lower lobes. Klebsiella pneumoniae is a common cause of lung abscesses and is usually monomicrobial (caused by a single species of bacteria). Risk factors include diabetes and chronic lung disease. A lung abscess due to Klebsiella can progress to massive pulmonary gangrene, a rare condition in which an entire section of the lung is completely destroyed. Half of all cases of pulmonary gangrene are caused by Klebsiella. Imaging in pulmonary gangrene shows multiple small cavities joining together to form a large cavity.
Mycobacterial
Mycobacteria that can cause cavitations include Mycobacterium tuberculosis and nontuberculous mycobacteria, most commonly Mycobacterium avium complex. Primary tuberculosis is caused by the initial infection with Mycobacterium tuberculosis and rarely results in the formation of lung cavities. 90% of people with primary tuberculosis are able to contain the infection and enter a latent phase. Reactivation tuberculosis, which is caused by the reactivation of latent tuberculosis, results in lung cavities visible on X-ray 30 to 50% of the time. There are frequently multiple cavities, and they most commonly occur in the apical and posterior segments of the upper lobes or the superior segment of the lower lobes. Cavitary tuberculosis is associated with worse outcomes, a higher rate of treatment failure, more frequent relapse after treatment, and a higher risk of transmitting the disease to others. Even after successful treatment with anti-tuberculosis drugs, 20-50% of patients with cavitary tuberculosis have persistent cavities, which results in decreased lung function and increased risk of opportunistic infections by Aspergillus fumigatus and other fungal pathogens.
Nontuberculous mycobacteria (NTM) are all mycobacterial species other than Mycobacteria tuberculosis (which causes tuberculosis) and Mycobacterium leprae (which causes leprosy). NTM are found everywhere in the environment but are most commonly found in soil and water. Lung disease is caused by inhaling or ingesting nontuberculous mycobacteria. Unlike tuberculosis, NTM infection is not transmitted from person to person. Although NTM lung infections can cause lung cavities, the most common finding on imaging is bronchiectasis, which may occur with or without cavities. Mycobacterium avium complex (MAC) is the most common cause of NTM lung disease in most countries, including the United States. Classically, MAC infection results in either upper lobe cavities in male smokers with COPD or bronchiectasis in thin, older women; however, it is possible to have both cavities and bronchiectasis in the same patient. Similar to tuberculosis, the presence of cavities in MAC infection is associated with worse outcomes. Mycobacterium kansasii, Mycobacterium xenopi, and the rapidly-growing Mycobacterium abscessus have also been associated with lung cavities.
Fungal Fungal infections that can cause cavitations include histoplasmosis, coccidioidomycosis, cryptococcosis, and aspergillosis. Aspergillosis, most commonly caused by Aspergillus fumigatus, can present in four different ways (listed in order of increasing severity): aspergilloma, allergic bronchopulmonary aspergillosis (ABPA), chronic necrotizing aspergillosis, and invasive aspergillosis. All of these are associated with lung cavities except for ABPA, which is a hypersensitivity response associated with bronchiectasis on imaging. An aspergilloma is an infection of a pre-existing lung cavity by Aspergillus species without tissue invasion and results in the formation of a fungal ball. Historically, tuberculosis was the most common cause of the lung cavity (and still is in areas where tuberculosis is endemic); however, the cavity can also be caused by sarcoidosis, bullae, bronchiectasis, or cystic lung disease. Chronic necrotizing aspergillosis and invasive aspergillosis are usually seen in immunocompromised people. Risk factors for chronic necrotizing aspergillosis include advanced age, alcoholism, diabetes, and mild immunosuppression. Invasive pulmonary aspergillosis is mainly seen in severely immunocompromised people, especially those with hematological malignancies (cancers of the blood), bone marrow transplant recipients, and people on long-term corticosteroid therapy, such as prednisone. Allogeneic bone marrow transplant recipients have the highest risk of getting invasive aspergillosis. Lung transplant recipients are also at high risk.
Parasitic