lung abscess

A lung abscess is a pocket of pus walled off inside the lung — much like a boil, but deep in lung tissue rather than on the skin. Infection destroys a patch of lung, and the dead, liquefied tissue and pus collect in a cavity. When that cavity connects to an airway, the person may suddenly cough up large amounts of foul-smelling phlegm.

It forms when a necrotizing infection — one that kills tissue — is not cleared, often after material is aspirated from the mouth or stomach into the lung, especially in people with reduced consciousness, swallowing problems or poor dental hygiene. The germs involved are frequently a mix that includes anaerobic bacteria from the mouth. On a chest X-ray or CT the cavity often shows a tell-tale air-fluid level where air sits above liquid pus.

Treatment is usually a prolonged course of antibiotics, sometimes for weeks, allowing the abscess to drain naturally through the airway as the patient coughs; physiotherapy and good drainage help. Most abscesses heal with medication alone, but a minority need drainage through the chest wall or, rarely, surgery if they do not respond.

A cavity in the lung is not always a simple abscess: tuberculosis, fungal infection and cavitating cancers can look similar on imaging, so the cause is confirmed with cultures and sometimes sampling rather than assumed.