Section 4. Lung and Airway Disorders

Chapter 43. Lung Abscess

Topic: Lung Abscess

Lung Abscess

A lung abscess is a pus-filled cavity in the lung surrounded by inflamed tissue and caused by an infection.

Causes

A lung abscess is usually caused by bacteria that normally live in the mouth or throat and that are inhaled 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 these defenses are impaired--for example, when a person is unconscious or very drowsy because of sedation, anesthesia, alcohol or drug abuse, or a disease of the nervous system.

In some people, particularly those older than age 40 who smoke, a lung tumor may lead to the formation of a lung abscess by blocking an airway (a bronchus). An abscess can form because secretions (mucus) can accumulate behind the tumor. Bacteria are able to accumulate in the secretions, and the obstruction prevents the bacteria-laden secretions from being brought back up through the airway where they would normally be coughed up; thus, the right conditions for bacterial infection are formed. Foreign objects that are inhaled (aspirated) may block an airway and also form the right conditions for bacterial infection.

Pneumonia caused by certain bacteria, such as Staphylococcus aureus or Legionella pneumophila, or fungi may lead to a lung abscess. Less common organisms may cause a lung abscess in a person who has a poorly functioning immune system. Rarely, bacteria or infected blood clots that travel through the bloodstream to the lung from another infected site in the body (septic pulmonary emboli) may cause a lung abscess.

Usually, a person develops only one lung abscess, but when several develop, they are typically in the same lung. If an infection reaches the lung through the bloodstream, many scattered abscesses may develop in both lungs. This problem is most common among addicts who inject drugs using dirty needles, which can also cause infection of the lining of the right side of the heart (endocarditis (see Section 3, Chapter 29)).

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. When a large abscess ruptures into an airway, pus may spread throughout the lung, causing widespread pneumonia and acute respiratory distress syndrome (see Section 4, Chapter 56). Sometimes an abscess ruptures into the pleural space (the space between the membrane layers covering the lungs and the chest wall), filling the space with pus, a condition called empyema. If an abscess destroys a blood vessel wall, serious bleeding may result, sometimes leading to death.

Symptoms and Diagnosis

The symptoms may start slowly or 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 certain bacteria from the mouth or throat tend to produce foul odors) or streaked with blood. The person also may feel chest pain with breathing, especially if the pleura is inflamed (pleurisy (see Section 4, Chapter 52)). 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, have a fever every day, and also have night sweats.

Chest x-rays nearly always reveal a lung abscess. However, when an x-ray only suggests an abscess, computed tomography (CT) of the chest can confirm the presence of a lung abscess and possibly determine its cause. Cultures of sputum from the lungs may help identify the organism causing the abscess, but this test is not always useful.

Treatment

Prompt, complete healing of a lung abscess requires the administration of antibiotics. These 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 usually requires several weeks or months of antibiotic therapy. Postural drainage may be used to help drain the abscess (see Section 4, Chapter 40).

Bronchoscopy (see Section 4, Chapter 56) is performed to confirm the presence of an obstruction when the cause is thought to be a blocked airway due to a tumor or a foreign object. Bronchoscopy may also be used to remove a foreign object or to help drain a lung abscess that does not respond to antibiotics.

About 5% of people with lung abscesses need additional treatment. Occasionally, an abscess requires drainage through a tube inserted through the chest wall and into the abscess. More often, 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.

The death rate for people with lung abscesses is about 5%. The rate is higher when the person is debilitated or has an impaired immune system, lung cancer, or a very large abscess.