Abscesses may be single or, less often, multiple. Although primary lung abscesses begin with necrotizing pneumonitis, cavitation is radiographically evident in most patients by the time lung abscess is diagnosed. The finding of air-fluid levels signifies rupture into the bronchial tree. As is the case with other pulmonary infections, examination of the sputum is crucial to diagnosis. In patients with primary lung abscesses, the sputum is often putrid and contains numerous polymorphonuclear leukocytes and an abundant mixed microbial flora.
Sputum cultures reveal only normal mouth flora.
Meaningful anaerobic bacteriology depends on obtaining, either by transtracheal aspiration or by bronchoscopy, specimens that have not traversed the oropharynx. Percutaneous needle aspiration can also be very helpful, both diagnostically and therapeutically. In a typical case of aspirational putrid lung abscess, these invasive procedures may not be necessary. They are important, however, if the diagnosis is uncertain. The isolation of a specific bacterial pathogen from expectorated sputum of patients with an otherwise typical primary abscess should be confirmed by transtracheal aspiration because such pathogens are often not present in selective lower tract specimens.