A lung abscess is an infection of the lung parenchyma resulting in a necrotic cavity containing pus.

Pulmonary abscess

• Incidence has decreased over the last 30 years as a result of antibiotic therapy.
• Lung abscess in patients age 50 and over is associated with primary lung neoplasia in 30% of the cases.
• Lung abscesses commonly coexist with empyemas.
• Risk factor population includes patients with:

1.Alcohol-related problems
2.Seizure disorders
3.Cerebrovascular disorders with dysphagia
4.Drug abuse
5.Esophageal disorders (e.g., scleroderma, esophageal carcinoma, etc.)
6.Poor oral hygiene
7.Obstructive malignant lung disease
8.Bronchiectasis

• Symptoms are generally insidious and prolonged, occurring for weeks to months
• Fever, chills, and sweats
• Cough
• Sputum production (purulent with foul odor)
• Pleuritic chest pain
• Hemoptysis
• Dyspnea
• Malaise, fatigue, and weakness
• Tachycardia and tachypnea
• Dullness to percussion, whispered pectoriloquy, and bronchophony

• The most important factor predisposing to lung abscess is aspiration.
• Following aspiration as a major predisposing factor is periodontal disease.
• Lung abscess is rare in an edentulous person.
• Approximately 90% of lung abscesses are caused by anaerobic microorganisms (Bacteroides fragilis, Fusobacterium nucleatum, Peptostreptococcus, microaerophilic Streptococcus).
• In most cases anaerobic infection is mixed with aerobic or facultative anaerobic organisms (S. aureus, E. coli, K. pneumoniae, P. aeruginosa).

Lung abscess may be primary or secondary.
• Primary lung abscess refers to infection from normal host organisms within the lung (e.g., aspiration, pneumonia).
• Secondary lung abscess results from other preexisting conditions (e.g., endocarditis, underlying lung cancer, pulmonary emboli).
Lung abscess may be acute or chronic.
• Acute lung abscess is present if symptoms are of less than 4 to 6 wk.
• Chronic lung abscess is present if symptoms are greater than 6 wk.

The differential diagnosis is similar to cavitary lung lesions:
• Bacterial (anaerobic, aerobic, infected bulla, empyema, actinomycosis, tuberculosis)
• Fungal (histoplasmosis, coccidioidomycosis, blastomycosis, aspergillosis, cyptococcosis)
• Parasitic (amebiasis, echinococcosis)
• Malignancy (primary lung carcinoma, metastatic lung disease, lymphoma, Hodgkin’s disease)
• Wegener’s granulomatosis, sarcoidosis, endocarditis, and septic pulmonary emboli

• The workup of a patient with lung abscess attempts to elicit a primary or a secondary cause.
• Blood tests are not specific in diagnosing lung abscesses.
• Most diagnoses are made from imaging studies; however, to diagnose a specific cause bacteriologic studies are needed.

• CBC with leukocytosis
• Bacteriologic studies

1.Sputum Gram stain and culture (commonly contaminated by oral flora)
2.Percutaneous transtracheal aspiration
3.Percutaneous transthoracic aspiration
4.Fiberoptic bronchoscopy using bronchial brushings or bronchoalveolar lavage are the most widely used intervention when trying to obtain diagnostic bacteriologic cultures
• Blood cultures on some occasions may be positive
• If an empyema is present, obtaining empyema fluid via thoracentesis may isolate the organism

• Chest x-ray examination makes the diagnosis of lung abscess showing the cavitary lesion with an air fluid level.
• Lung abscesses are most commonly found in the posterior segment of the right upper lobe.
• Chest CT scan can localize and size the lesion and assist in differentiating lung abscesses from other pathologic processes (e.g., tumor, empyema, infected bulla, etc.) ( Fig. 1–3 ).

• Oxygen therapy
• Postural drainage
• Respiratory therapy maneuvers

• Penicillin 1 to 2 million units IV q4h until improvement (e.g., afebrile, decrease in sputum production, etc.) followed by penicillin VK 500 mg PO qid for the next 2 to 3 wk but usually requiring longer 6- to 8-wk courses.
• Metronidazole is given with penicillin at doses of 7.5 mg/kg IV q6h followed by PO 500 mg bid to qid dosing.
• Clindamycin is an alternative choice if concerned about penicillinresistant organisms. The dose is 600 mg IV q8h until improvement, followed by 300 mg PO q6h.

• Brochoscopy to assist with drainage and/or diagnosis is indicated in patients who fail to respond to antibiotics or if there is suspected underlying malignancy.
• Surgery is indicated on rare occasions (<10 abscess="abscess" below.="below." br="br" complications="complications" in="in" lung="lung" mentioned="mentioned" of="of" patients="patients" with="with">

• Over 95% of patients are cured with the use of antibiotics alone.
• Complications of lung abscesses include:

1.Empyema

2.Massive hemoptysis

3.Pneumothorax

4.Bronchopleural fistula

10• Mortality is low in communityacquired lung abscess (2.5%)
• Hospital-acquired lung abscess carry a high mortality rate (65%)

If lung abscess is present, consultation with pulmonary and infectious disease specialist is recommended.

COMMENTS
• Complications of lung abscesses include:

1.Empyema
2.Bronchopleural fistula
3.Hepatobronchial fistula
4.Brain abscess
5.Bronchiectasis
• Refractory cases are usually the result of:

1.Large cavity size (>6 cm)
2.Recurrent aspiration
3.Thick-walled cavities
4.Underlying lung carcinoma
5.Empyema formation
• Necrotizing pneumonia is similar to a lung abscess but differs in size (<2 and="and" br="br" cavitory="cavitory" cm="cm" diameter="diameter" in="in" lesions="lesions" multiple="multiple" number="number" suppurative="suppurative" usually="usually">

Cassiere HA, Niederman MS: Aspiration pneumonia, lipoid pneumonia, and lung abscess. In Baum GL et al: Textbook of pulmonary diseases, ed 6, New York, 1998, Lippincott-Raven.

Finegold SM: Lung abscess. In Mandell, Douglas, and Bennett’s principles and practice of infectious diseases, ed 5, New York, 2000, Churchill Livingstone.

Mwandumba HC, Beeching NJ: Pyogenic lung infections: factors for predicting clinical outcome of lung abscess and thoracic empyema, Curr Opin Pulm Med 6(3):234, 2000.

Rowe S, Cheadle WG: Complications of nosocomial pneumonia in the surgical patient, Am J Surg 179(2A suppl):63s, 2000.

Wiedemann HP, Rice TW: Lung abscess and empyema, Semin Thorac Cardiovasc Surg 7:119, 1995