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 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 abuse, or a disease of the nervous system. 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). Another cause of lung abscess is Staphylococcus aureus as well as methicillin-resistant Staphylococcus aureus (MRSA), which is a serious infection. This usually occurs in young, previously healthy adults or children, especially if they have influenza.
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 tumor. 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 lung 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. The cavity may become an inactive part of the lung, or it may require surgical removal. 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. 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: fatigue, loss of appetite, sweating, fever, and a cough that brings up sputum. 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 with breathing, especially if the lining on the outside of the lungs and inside of the chest wall (pleura) is inflamed (a condition called pleurisy—see Pleural and Mediastinal Disorders: 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 a lung abscess. However, how a lung abscess appears on an x-ray is sometimes similar to how other conditions, such as cancer, sarcoidosis, or Wegener's granulomatosis, appear on x-ray. Sometimes, an abscess is only found when computed tomography (CT) of the chest is done. Cultures of sputum may help identify the organism causing the abscess, but this test is usually not useful except for excluding MRSA, tuberculosis, and fungal infections.
Treatment requires antibiotics. Antibiotics are initially given intravenously in most cases and later by mouth when the person has improved and the fever has resolved. Antibiotic treatment continues until the symptoms disappear and a chest x-ray shows that the abscess has disappeared. Such improvement may require several weeks or even months of antibiotic therapy.
Bronchoscopy (see Diagnosis of Lung Disorders: Bronchoscopy) is often done when the abscess is thought to be the result of a tumor or a foreign object blocking the airway. Rarely, a lung abscess may have to be drained through a tube inserted through the chest wall and into the abscess, 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, lung cancer, or a very large abscess.
Last full review/revision January 2008 by John G. Bartlett, MD