A lung abscess is a pus-filled cavity in the lung surrounded by inflamed tissue and caused by an infection.
A lung abscess is usually caused by bacteria that normally live in the mouth or throat and that are inhaled (aspirated) into the lungs, resulting in an infection. Often, gum (periodontal) disease is the source of the bacteria that cause a lung abscess. The body has many defenses (such as a cough) to help prevent bacteria from getting into the lungs. Infection occurs primarily when a person is unconscious or very drowsy because of sedation, anesthesia, alcohol or drug use, or a disease of the nervous system and is thus less able to cough to clear the aspirated bacteria. In people whose immune system functions poorly, a lung abscess may be caused by organisms that are not typically found in the mouth or throat, such as fungi or Mycobacterium tuberculosis (the organism that causes tuberculosis). Other bacteria that can cause lung abscesses are streptococci and staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA), which is a serious infection.
Obstruction of the airways also can lead to abscess formation. If the branches of the windpipe (bronchi) are blocked by a tumor or a foreign object, an abscess can form because secretions (mucus) can accumulate behind the obstruction. Bacteria sometimes enter these secretions. The obstruction prevents the bacteria-laden secretions from being coughed back up through the airway.
Less commonly, abscesses result when bacteria or infected blood clots travel through the bloodstream to the lung from another infected site in the body (septic pulmonary emboli).
Usually, people develop only one lung abscess as a result of aspiration or airway obstruction. If several abscesses develop, they are usually in the same lung. When an infection reaches the lungs through the bloodstream, however, many scattered abscesses may develop in both lungs. This problem is most common among people who inject drugs using dirty needles or unsterile methods.
Eventually, most abscesses rupture into an airway, producing a lot of sputum that gets coughed up. A ruptured abscess leaves a cavity in the lung that is filled with fluid and air. Sometimes an abscess ruptures into the space between the lungs and the chest wall (pleural space), filling the space with pus, a condition called empyema (see Types of fluid). Very rarely, if an abscess destroys a blood vessel wall, it may lead to serious bleeding.
Symptoms most commonly start slowly. However, depending on the cause of the abscess, symptoms can occur suddenly. Early symptoms resemble those of pneumonia:
The sputum may be foul smelling (because bacteria from the mouth or throat tend to produce foul odors) or streaked with blood. People also may feel chest pain as they breathe, especially if the lining on the outside of the lungs and inside of the chest wall (pleura) is inflamed (a condition called pleurisy—see Symptoms). Many people have these symptoms for weeks or months before seeking medical attention. These people have chronic abscesses and, in addition to the other symptoms, lose a substantial amount of weight and have daily fever and night sweats. In contrast, lung abscesses caused by Staphylococcus aureus or MRSA can be fatal within days, sometimes even hours.
Chest x-rays nearly always reveal the lung abscess as a cavity filled with fluid and air. However, in an x-ray, a lung abscess sometimes resembles another condition, such as cancer or sarcoidosis. Sometimes an abscess is only found when computed tomography (CT) of the chest is done. Doctors may take a sample of sputum and try to grow (culture) the organism causing the abscess, but this test is usually not useful except for excluding certain organisms. Bronchoscopy (see Bronchoscopy) may be done to obtain samples of lung secretions or tissue for culture if, for example,
If the immune system is impaired, organisms that do not usually cause lung abscesses may be causing the abscess. Unusual organisms must be identified as soon as possible because they are treated differently from the usual organisms that cause lung abscess.
Treatment requires antibiotics. Antibiotics are initially given through a vein (intravenously) in most cases and later by mouth when the person's condition has improved and the fever has resolved. Antibiotic treatment continues until the symptoms disappear and a chest x-ray shows that the abscess has cleared up. Such improvement usually requires 3 to 6 weeks of antibiotic therapy, but a longer treatment period may be needed.
When the abscess is thought to be the result of a tumor or a foreign object blocking the airway, bronchoscopy is sometimes used for treatment, such as removing the foreign object. Rarely, an empyema has to be drained through a tube inserted through the chest wall, or infected lung tissue may have to be removed surgically. Sometimes an entire lobe of a lung or even an entire lung has to be removed.
Most people are cured. Treatment is less likely to be successful when the person is debilitated or has an impaired immune system or when a bronchus is blocked by a tumor.
Last full review/revision September 2014 by Sanjay Sethi, MD