Lung abscess: Necrosis of the pulmonary tissue and formation of cavities containing

necrotic debris or fluid caused by microbial infection.

• The formation of multiple small (<2 cm) abscesses is occasionally referred to as

necrotizing pneumonia.

• Both lung abscess and necrotizing pneumonia are manifestations of a similar pathologic process.

• Failure to recognize and treat lung abscess is associated with poor clinical outcomes.

 

Classification of Lung Abscess

• Lung abscesses can be classified based on the duration and the likely etiology

• Acute abscesses are less than 4-6 weeks old

• Chronic abscesses are of longer duration

• The primary abscess is infectious in origin, caused by aspiration or pneumonia in the healthy

host

• The secondary abscess is caused by:

A preexisting condition (e.g. obstruction)

Spread from an extrapulmonary site

Bronchiectasis

An immunocompromised state

• Lung abscesses can be further characterized by the responsible pathogen, such as:

Staphylococcus lung abscess

Anaerobic infections

Aspergillus lung abscess

 

Pathophysiology

• Most frequently, the lung abscess arises as a complication of aspiration pneumonia

caused by mouth anaerobes.

• A bacterial inoculum from the gingival crevice reaches the lower airways, and infection is

initiated because the bacteria are not cleared by the patient's host defense mechanism.

• This results in aspiration pneumonitis and progression to tissue necrosis 7-14 days later,

resulting in the formation of lung abscess

• Other mechanisms for lung abscess formation include bacteremia or tricuspid valve

endocarditis, causing septic emboli (usually multiple) to the lung.

• The oral anaerobe fusobacterium necrophorum is the most common pathogen.

 

Risks of Developing Lung Abscess

• Patients at the highest risk for developing lung, the abscess has the following risk factors:

Periodontal disease

Seizure disorder

Alcohol abuse

Dysphagia

Other patients at high risk for developing lung abscess include individuals with an

inability to protect their airways from massive aspiration because of a diminished gag

or cough reflex, caused by a state of impaired consciousness (e.g. from alcohol or

other CNS depressants, general anesthesia, or encephalopathy)

Causes of Lung Abscess

• An abscess may develop as an infectious complication of a preexisting bulla or lung cyst.

• The abscess may develop secondary to carcinoma of the bronchus; the bronchial

obstruction causes post obstructive pneumonia, which may lead to abscess formation.

• Published reports since the beginning of the antibiotic area have established that

anaerobic bacteria are the most significant pathogens in lung abscess. The most common

anaerobes are

Peptostreptococcus species

Bacteroides species

Fusobacterium species

Microaerophilic streptococci

• Aerobic bacteria that may infrequently cause lung abscesses include

Staphylococcus aureus

Streptococcus pyogenes

Streptococcus pneumoniae (rarely)

Klebsiella pneumoniae

Haemophilus influenzae

Pseudomonas aeruginosa

Actinomyces species

Nocardia species

Gram-negative bacilli

• Nonbacterial and atypical bacterial pathogens may also cause lung abscesses, usually in

the immunocompromised host these microorganisms include

Parasites (Paragonimus and Entamoeba species)

Fungi (e.g. Aspergillus, Cryptococcus, Histoplasma, Blastomyces, and Coccidioides

species)

Mycobacterium species

Epidemiology of Lung Abscess

• Frequency

The frequency of lung abscesses in the general population is not known.

• Sex

A male predominance for a lung abscess is reported in published case series.

• Age

Lung abscesses likely occur more commonly in elderly patients because of the

increased incidence of periodontal disease and the increased prevalence of dysphagia

and aspiration.

Mortality/Morbidity

• Most patients with primary lung abscesses improve with antibiotics, with cure rates

documented at 90-95%

• Host factors associated with a poor prognosis include advanced age, debilitation,

malnutrition, human immunodeficiency virus infection or other forms of

immunosuppression, malignancy, and duration of symptoms greater than 8 weeks.

• The mortality rate for patients with underlying immunocompromised status or bronchial

obstruction who develop lung abscess may be as high as 75%.

• Frequently hospital-acquired aerobic organisms are associated with poor outcomes

Clinical Features of Lung Abscess

History

• Symptoms depend on whether the abscess is caused by anaerobic or other bacterial

infection.

• Anaerobic infection in lung abscess

Patients often present with indolent symptoms that evolve over a period of weeks to

months.

The usual symptoms are fever, cough with purulent and copious sputum production,

night sweats, anorexia, and weight loss.

The expectorated sputum characteristically is foul-smelling and bad tasting.

Patients may develop hemoptysis or pleurisy.

• Other pathogens in lung abscess

These patients generally present with conditions that are more emergent in nature and

are usually treated while they have bacterial pneumonia.

Cavitation occurs subsequently as parenchymal necrosis ensues.

Abscesses from fungi, Nocardia species and Mycobacteria species tend to have an

indolent course and gradually progressive symptoms.

Physical Examination

• The findings on physical examination of a patient with lung abscess are variable.

• Physical findings may be secondary to associated conditions such as underlying

pneumonia or pleural effusion.

• Patients with lung, abscesses may have a low-grade fever in anaerobic infections and

temperatures higher than 38.5°C in other infections.

• Generally, patients with lung abscesses have evidence of gingival disease.

• Clinical findings of concomitant consolidation may be present (e.g. dullness to

percussion, bronchial breath sounds, coarse inspiratory crackles)

• Evidence of pleural friction rub and signs of associated pleural effusion, empyema, and

pyopneumothorax may be present. Signs include the contra-lateral shift of the mediastinum,

dullness to percussion, and absent breath sounds over the effusion.

• Digital clubbing may develop rapidly

 

Diagnosis and Management of Lung Abscess

Differential Diagnosis

• Pulmonary tuberculosis

• Empyema thoracic

• Lung cancer

• Pneumonia

• Pulmonary embolism

• Infective Endocarditis

• Pneumocystis Jirovecii Pneumonia (Pneumocystis Carinii Pneumonia)

• Wegener Granulomatosis

• Hydatid Cysts

Diagnosis of Lung Abscess

• Refer the patient to a higher center for laboratory studies and imaging studies

• Perform pre-referral treatment

IV fluids

Antibiotics, and analgesics

Monitor vital signs

• Refer the patient to a higher center (hospital) for proper management

Prevention

• Prevention of aspiration is important to minimize the risk of lung abscess.

• Early intubation in patients who have diminished ability to protect the airway from

massive aspiration (cough, gag reflexes), should be considered.

• Positioning patient in the supine position at a 30° reclined angle minimizes the risk of

aspiration. Vomiting patients should be placed on their sides.

• Improving oral hygiene and dental care in elderly and debilitated patients may decrease

the risk of anaerobic lung abscess.

Complications of Pulmonary Abscess

• Rupture into pleural space causing empyema

• Pleural fibrosis

• Trapped lung

• Respiratory failure

• Bronchopleural fistula

• Pleural cutaneous fistula

• In a patient with coexisting empyema and lung abscess, draining the empyema while

continuing prolonged antibiotic therapy is often necessary

Prognosis

• The prognosis for lung abscess following antibiotic treatment is generally favorable.

• Over 90% of lung abscesses are cured with medical management alone unless caused by

bronchial obstruction secondary to carcinoma.

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