What is a lung abscess?
A lung abscess, or pulmonary abscess, is a localized collection of pus associated with necrosis of the lung tissue. The abscess is basically a cavity that forms in the lung tissue, walled off by fibrous tissue and filled with pus, cellular debris, microbes and white blood cells. A lung abscess is the consequence of infectious microorganisms, particularly bacteria, entering or invading the lung tissue. It may occur either as a solitary abscess (single) or multiple abscesses.
Any pathogen can cause abscess formation but anaerobic bacteria are the most likely microorganisms to do so. If the abscess develops in an otherwise healthy lung and respiratory tract, then it is considered as a primary abscess. It can however develop as a complication of some underlying lung pathology – secondary abscess. The size of the abscess can vary from a few millimeters in diameter to several centimeters (up to 5 to 6 cm). The abscess may communicate with an air passage (usually the bronchus) and then partially drain and become filled with air. The pus in this case is expectorated (sputum). However, if the abscess extends into the pleural cavity, possibly via a fistula, then it may lead to empyema (fluid around lungs – pus).
What causes a lung abscess?
The most common cause of a lung abscess is when microorganisms from the mouth pass through the respiratory tract to reach the lung tissue. This causes aspiration pneumonia and the death and destruction of the lung tissue (necrotizing pneumonia) progresses to abscess formation. It is more likely to occur if the patient has poor oral hygiene, several tooth cavities, gingivitis or periodontitis.
Aspiration occurs in a person who is intoxicated (alcohol, narcotic drugs) or sedated (anesthesia, opioid painkillers). Those with neurological disorders, particularly the elderly, and other causes of swallowing difficulties (dysphagia) are more prone to aspiration pneumonia. Saliva, food or inhaled foreign objects may carry these pathogenic microorganisms into the respiratory system. Most cases are due to anaerobic bacteria although mixed bacteria (anaerobic and aerobic) account for almost half of all cases. Other pathogens include fungi, mycobacteria and parasites.
A lung abscess may also be caused by an infection spreading from a neighboring site (direct infiltration), like with a liver abscess, subphrenic abscess or pleural infection (infectious pleuritis), or from distant sites via the blood stream (hematogenous spread) like with bacteremia or septic embolus associated with tricuspid endocarditis. It may also develop as a secondary infection in pre-existing respiratory disease like bronchiectasis or bronchial/lung cancer.
Signs and Symptoms of a Lung Abscess
Most of the signs and symptoms are non-specific and may be seen in most other infectious diseases of the respiratory tract and lungs – productive cough, breathlessness, pleuritic chest pain and fever often with rigors and profuse perspiration. However, the expectoration of copious amounts of foul smelling sputum, which is often blood-stained, should raise the concern about a lung abscess. Patients will also report that the sputum is foul tasting leaving a persistent bad taste in the mouth. Digital clubbing is seen after several weeks.
Rapid breathing (tachypnea), rapid heart rate (tachycardia) and abnormal breathing sounds (crackles / bronchial breathing) associated with pulmonary consolidation and pleural effusions may also be seen. General symptoms include dehydration and weight loss.