Lung cavity
Lung cavity | |
---|---|
Other names | Pulmonary cavity, lung cavitary lesion, lung cavitation |
Chest X-ray of a person with advanced tuberculosis: Infection in both lungs is marked by white arrow-heads, and the formation of a cavity is marked by black arrows. | |
Specialty | Pulmonology |
Complications | Aspergilloma |
Causes | Tuberculosis, Lung cancer |
A lung cavity or pulmonary cavity is an abnormal, thick-walled, air-filled space within the lung.[1] Cavities in the lung can be caused by infections, cancer, autoimmune conditions, trauma, congenital defects,[2] or pulmonary embolism.[3] The most common cause of a single lung cavity is lung cancer.[4] Bacterial, mycobacterial, and fungal infections are common causes of lung cavities.[5] Globally, tuberculosis is likely the most common infectious cause of lung cavities.[6] Less commonly, parasitic infections can cause cavities.[5] Viral infections almost never cause cavities.[7] 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.[3]
Diagnosis of a lung cavity is made with a
The presence of lung cavities is associated with worse outcomes in lung cancer[7] and tuberculosis;[8] however, if a lung cancer develops cavitation after chemotherapy and radiofrequency ablation, that indicates a good response to treatment.[2]
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”.[9] Pathologically, a cavity is “usually produced by the expulsion or drainage of a necrotic part of the lesion via the bronchial tree.”[9]
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.[5] Lung cysts are the most common mimics of lung cavities.[2] Cavities and cysts are similar in that they are both abnormal, air-containing spaces with clearly defined walls.[3] The difference between cavities and cysts is that cavities are thick walled, while cysts are thin walled.[3] Generally, cavities have walls that are at least 5 mm thick, while cysts have walls that are 4 mm or less,[3] and often less than 2 mm.[2]
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.
Areas of emphysema are abnormal, air-filled spaces that usually do not have visible walls,[5] and bullae are very thin walled (<1 mm).[2] Cystic bronchiectasis is irreversible bronchial dilation, which is permanent widening of the bronchioles (small airways) in the lung.[2] 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.[5]
Infectious causes
Bacterial, mycobacterial, and fungal infections are common causes of lung cavities.[5] Globally, tuberculosis is likely the most common infectious cause of lung cavities.[6] Less commonly, parasitic infections can cause cavities.[5] 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.[7]
Bacterial
Bacteria can cause lung cavities in one of two ways; they can either enter the lung through the
Pneumonia can lead to the development of a lung abscess,[4] which is a pus-containing necrotic lesion of the lung parenchyma (lung tissue).[5] 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).[4] An abscess can occur anywhere in the lung.[4] 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),[7] older age, diabetes mellitus, drug abuse, and artificial ventilation.[2] 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.[2] 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.[7] 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.[7]
Mycobacterial
Mycobacteria that can cause cavitations include Mycobacterium tuberculosis and nontuberculous mycobacteria, most commonly Mycobacterium avium complex.[7] 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,[2] results in lung cavities visible on X-ray 30 to 50% of the time.[7] 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.[7] 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.[8] 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.[8]
Nontuberculous mycobacteria (NTM) are all mycobacterial species other than Mycobacteria tuberculosis (which causes tuberculosis) and
Fungal
Fungal infections that can cause cavitations include
Parasitic
Parasitic infections associated with cavitations include echinococcosis and paragonimiasis.[7] Echinococcus is a tapeworm that most commonly infects dogs; people become infected by ingesting food or water that contains Echinococcus eggs. This results in cysts forming in the body, most commonly in the liver, but lung involvement is seen in 10-30% of cases. The cysts in the lung sometimes look like cavities on imaging.[7] Paragonimus westermani, also called the lung fluke, is a flatworm which is transmitted by eating freshwater crabs or crayfish containing metacercaria (the infective form of the tapeworm). They mature into adult lung flukes in the lung, where cavitations may be seen in 15-59% of cases. Paragonimiasis is common in East Asia and Southeast Asia.[7]
Noninfectious causes
Lung cancer
The most common cause of a single lung cavity is lung cancer.
Autoimmune
Autoimmune causes of lung cavities include granulomatosis with polyangiitis, rheumatoid arthritis, and rarely necrotizing sarcoidosis[2] (less than 1% of people with sarcoidosis develop lung cavities).[4] Ankylosing spondylitis, eosinophilic granulomatosis with polyangiitis, and systemic lupus erythematous rarely cause lung cavities.[2]
Pulmonary embolism and septic emboli
Trauma
Pulmonary contusion (lung bruise) from blunt chest trauma causes bleeding into the alveoli (air sacs) and can cause small cavities to form that are called traumatic pulmonary pseudocysts (TPP). This is rare, as less than 3% of lung injuries lead to TPP. It can occur at any age, but is more common in children and adults under the age of 30. Although it can occur anywhere in the lung, it is most common in the lower lobes. TPP usually resolves on its own within four weeks.[2]
Congenital
See also
- Focal lung pneumatosis, article comparing lung blebs, bullae, cysts, and cavities
References
- ^ Bell, Daniel, Gaillard, Frank. "Pulmonary cavities". Radiopedia. Retrieved 12 February 2021.
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