A lung abscess is an infection of the lung parenchyma resulting in a necrotic cavity containing pus.
PHYSICAL FINDINGS AND CLINICAL PRESENTATION
● Symptoms are generally insidious and prolonged, occurring for weeks to months
● Fever, chills, and sweats
● Sputum production (purulent with foul odor)
● Pleuritic chest pain
● Malaise, fatigue, and weakness
● Tachycardia and tachypnea
● Dullness to percussion, whispered pectoriloquy, and bronchophony
● Amphoric breath sounds (low-pitched sound of air moving across a large open cavity)
● 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).
Pulmonary actinomycosis will also generate lung abscess.
● In most cases, anaerobic infection is mixed with aerobic or facultative anaerobic organisms (S. aureus, E. coli, K. pneumoniae, P. aeruginosa).
● Parasitic organisms, including Paragonimus westermani and Entamoeba histolytica ● Fungi, including Aspergillus, Cryptococcus, Histoplasma, Blastomyces, and Coccidioides
● Immunocompromised hosts may become infected with Aspergillus, mycobacteria, Nocardia, Legionella micdadei, and Rhodococcus equi.
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 less than 4 to 6 weeks.
● Chronic lung abscess is present if symptoms are longer than 6 weeks.
The differential diagnosis is similar to that for cavitary lung lesions:
● Bacterial (anaerobic, aerobic, infected bulla, empyema, actinomycosis, tuberculosis)
● Fungal (histoplasmosis, coccidioidomycosis, blastomycosis, aspergillosis, cryptococcosis)
● Parasitic (amebiasis, echinococcosis)
● Malignancy (primary lung carcinoma, metastatic lung disease, lymphoma, Hodgkin’s disease)
● Wegener’s granulomatosis, sarcoidosis, endocarditis, septic pulmonary emboli
● 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 is 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 reveals cavitary lesion with an air fluid level .
● Lung abscesses are most commonly found in the posteriorn 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.)
● Penicillin, 1 to 2 million U IV, every 4 hours until improvement (e.g., afebrile, decrease in sputum production) followed by penicillin VK 500 mg PO daily for the next 2 to 3 weeks but usually requiring longer 6- to 8-week courses
● Metronidazole is given with penicillin at doses of 7.5 mg/kg IV every 6 hours, followed by metronidazole PO, 500 mg twice to four times daily.
● Clindamycin is an alternative choice if concerned about penicillin-resistant organisms. The dose is 600 mg IV every
8 hours until improvement, followed by 300 mg PO every 6 hours.