nodules, patchy to confluent areas of opacification, or even lobar pneumonia. Infection is
usually bilateral and multifocal, with the lower lobes affected more often.Klebsiellaclassically
occurs in older, alcoholic patients. The infection manifests as lobar opacification with an
exuberant inflammatory reaction, resulting in bulging fissures and a high incidence of effusion
and empyema compared with other organisms.Pseudomonasaffects debilitated, chronically
ventilated patients in particular. Infection may occur via the tracheobronchial tree, resulting in
patchy opacities and abscess formation, or hematogenously, which is seen as diffuse, bilateral
ill-defined nodular opacities (37).
Mimics of Cavitary Pneumonia
Septic Emboli
Cavitations caused by septic emboli may be thick or thin walled on chest radiographs and CT.
On CT, the lesions are peripherally distributed and frequently have associated feeding vessels
(Fig. 23). The lesions may be at different stages of development and healing (41).
Aspergillosis
Invasive pulmonary aspergillosis is another entity that frequently results in focal lung
infarctions and cavitary formation. The organism invades small blood vessels in the lung, the
early appearance of which is relatively small pulmonary nodules with surrounding
hemorrhage seen as ground-glass opacity secondary to hemorrhagic infarction, the “CT
halo” sign (Fig. 24). The vessel(s) involved can sometimes be identified (“feeding vessel” sign).
The classic “air crescent” sign appears during the healing process and is due to separation of
Figure 23 CT scan of the chest in a 30-year-
old male with endocarditis demonstrates multi-
ple nodular lesions throughout both lungs, some
cavitating, as well as left lower lobe pneumonia.
The nodular lesions represent septic pulmonary
emboli.Figure 24 CT scan of the chest in an
immunocompromised 29-year-old male demon-
strates a thick-walled cavitary lesion in the right
lung apex. Additional nodular lesions with
surrounding ground-glass opacity, some of
which were cavitating, were also seen through-
out both lungs. The findings combined with the
clinical information are highly compatible with
invasive aspergillosis.96 Luongo et al.