Lung abscess and necrotizing pneumonia. Lung abscesses are cavities associated with necrosis caused by a microbial infection. The term necrotizing pneumonia typically is used when there are multiple smaller (smaller than 2 cm) associated lung abscesses, although both lung abscess and necrotizing pneumonia represent a similar pathophysiologic process and are along the same continuum. Lung abscess is suspected with the presence of predisposing risk factors to aspiration (e.g. alcoholism) and poor dentition. History of cough, fever, putrid sputum, night sweats, and weight loss may indicate subacute or chronic development of a lung abscess. Physical examination might be significant for signs of pneumonia and gingivitis.
Organisms that cause lung abscesses include anaerobes (most common), TB, methicillin-resistant Staphylococcus aureus (MRSA), post-influenza illness, endemic fungi, and Nocardia, among others.4 In immunocompromised patients, more common considerations include TB, Mycobacterium avium complex, other mycobacteria, Pseudomonas aeruginosa, Nocardia, Cryptococcus, Aspergillus, endemic fungi (e.g. Coccidiodes in the Southwest and Histoplasma in the Midwest), and, less commonly, Pneumocystis jiroveci.4 The likelihood of each organism is dependent on the patient’s risk factors. Initial laboratory testing includes sputum and blood cultures, as well as serologic testing for endemic fungi, especially in immunocompromised patients.
Imaging may reveal a cavitary lesion in the dependent pulmonary segments (posterior segments of the upper lobes or superior segments of the lower lobes), at times associated with a pleural effusion or infiltrate. The most common appearance of a lung abscess is an asymmetric cavity with an air-fluid level and a wall with a ragged or smooth border. CT scan is often indicated when X-rays are equivocal and when cases are of uncertain cause or are unresponsive to antibiotic therapy. Bronchoscopy is reserved for patients with an immunocompromising condition, atypical presentation, or lack of response to treatment.
For those cavitary lesions in which there is a high degree of suspicion for lung abscess, empiric treatment should include antibiotics active against anaerobes and MRSA if the patient has risk factors. Patients often receive an empiric trial of antibiotics prior to biopsy unless there are clear indications that the cavitary lung lesion is related to cancer. Lung abscesses typically drain spontaneously, and transthoracic or endobronchial drainage is not usually recommended as initial management due to risk of pneumothorax and formation of bronchopleural fistula.
Lung abscesses should be followed to resolution with serial chest imaging. If the lung abscess does not resolve, it would be appropriate to consult thoracic surgery, interventional radiology, or pulmonary, depending on the location of the abscess and the local expertise with transthoracic or endobronchial drainage and surgical resection.
Septic emboli. Septic emboli are a less common cause of cavitary lung lesions. This entity should be considered in patients with a history of IV drug use or infected indwelling devices (central venous catheters, pacemaker wires, and right-sided prosthetic heart valves). Physical examination should include an assessment for signs of endocarditis and inspection for infected indwelling devices. In patients with IV drug use, the likely pathogen is S. aureus.
Oropharyngeal infection or indwelling catheters may predispose patients to septic thrombophlebitis of the internal jugular vein, also known as Lemierre’s syndrome, a rare but important cause of septic emboli.5 Laboratory testing includes culture for sputum and blood and culture of the infected device if applicable. On chest X-ray, septic emboli commonly appear as nodules located in the lung periphery. CT scan is more sensitive for detecting cavitation associated with septic emboli.
Diagnosis of Noninfectious Causes
Upon identification of a cavitary lung lesion, noninfectious etiologies must also be entertained. Noninfectious etiologies include malignancy, rheumatologic diseases, pulmonary embolism, and other causes. Important components in the clinical presentation include the presence of constitutional symptoms (fevers, weight loss, night sweats), smoking history, family history, and an otherwise complete review of systems. Physical exam should include evaluation for lymphadenopathy, cachexia, rash, clubbing, and other symptoms pertinent to the suspected etiology.