All of the following statements regarding lung abscesses are true EXCEPT:
ExplanationLung abscess represents necrosis and cavitation of the lung following microbial infection. Lung abscesses can be single or multiple but usually are marked by a single dominant cavity >2 cm in diameter. Although the incidence of lung abscesses has decreased in the postantibiotic era, they are still a source of signifcant morbidity and mortality. Lung abscesses are usually characterized as either primary (~80% of cases) or secondary. Primary lung abscesses usually arise from aspiration, are often caused principally by anaerobic bacteria, and occur in the absence of an underlying pulmonary or systemic condition. Patients at particular risk for aspiration, such as those with altered mental status, alcoholism, drug overdose, seizures, bulbar dysfunction, prior cerebrovascular or cardiovascular events, or neuromuscular disease, are most commonly afected. In addition, patients with esophageal dysmotility or esophageal lesions (strictures or tumors) and those with gastric distention and/or gastroesophageal refux, especially those who spend substantial time in the recumbent position, are at risk for aspiration. It is widely thought that colonization of the gingival crevices by anaerobic bacteria or microaerophilic streptococci (especially in patients with gingivitis and periodontal disease), combined with a risk of aspiration, is important in the development of lung abscesses. Secondary lung abscesses arise in the setting of an underlying condition, such as a postobstructive process (e.g., a bronchial foreign body or tumor) or a systemic process (e.g., HIV infection or another immunocompromising condition). In Lemierre syndrome, an infection begins in the pharynx (classically involving Fusobacterium necrophorum) and then spreads to the neck and the carotid sheath (which contains the jugular vein) to cause septic thrombophlebitis. Because most cases of lung abscess occur in the context of reclining aspiration, the dependent lobes of the lung are most vulnerable. The dependent lobes include the superior segment of the lower lobes and the posterior segment of the upper lobes, with the right lung more commonly involved than the left lung. The middle lobe and the lingula are the most ventral lobes and are therefore nondependent in the supine position.
