A cavity on chest X-ray is a thick walled air filled space in the lung. This can be associated with a nodule, mass (greater than 3 cm in size) or area of consolidated abnormal lung. There can be an air-fluid level inside. Lung cavities can be a result of infection, inflammation, cancer or you can be born with a cavity in the lung. There can be one or multiple cavities in the lung on chest X-ray.
Cancers of the lung can appear as a mass with a cavity inside. Most commonly these are squamous cell cancers associated with smoking. These are often large irregular masses with an air filled cavity components. Spread of cancer to the lung can also appear as a nodule or mass with a cavity inside. Sometimes after treatment, cancer in the lungs can develop cavities.
Infection can also appear as cavities in the lung. Tuberculosis can appear as a pulmonary cavity or opacification of lung with cavitation, usually in the posterior upper part of the lungs. A pneumonia can develop cavitation. A lung abscess or pocket of infected fluid in the lung will look like a cavity. Fungal infection of the lung can also have cavities.
Septic emboli will look like multiple cavitary nodules. These are infectious particles which travel to the lungs via the arteries of the lung. Septic emboli can travel to the lung from other infected sites in the body, like lines and heart valves. On X-ray, this will appear as nodules with cavitation of varying size.
Vascular causes of the lungs can also cause cavitation abnormalities. An infarct or area of dead lung tissue can rarely have cavitation. This most commonly occurs as a result of pulmonary embolism to the lung. Disease of blood vessels caused by vasculitis can cause areas of cavitation in the lung. Some people are born with abnormalities in their lungs which cause pulmonary cavities. These include congenital pulmonary airway malformation and sequestration.
Lung cavities have many different causes as detailed above. The appearance on X-ray in combination with the history is important to arrive at a diagnosis. In some cases, further testing will be needed to include biopsy. Often CT scan will be done. This will often narrow the possibilities because additional findings related to cancer, blood clots, infections may be present.