infected necrotic lung from normal lung parenchyma or an aspergilloma that develops within
a preexistent cavity (Fig. 25). Aspergillomas, which are not frankly angioinvasive in contrast to
invasive aspergillosis, but which may cause hemoptysis or may be asymptomatic, move freely
within the cavity and thus should change position between prone and supine imaging, a
helpful identifying feature (37,38).
Tuberculosis
Tuberculous cavitations have a preponderance for the upper lobes. The inner wall of a
tuberculous lesion can be either smooth or irregular in appearance (Fig. 26) (42).
Clinical and Radiologic Diagnosis of Diffuse Bilateral Pneumonia
Truly diffuse pneumonias are often viral in etiology. The infections can be divided into two
broad categories: those in immunocompetent hosts, most often influenza A and B, and those in
immunocompromised hosts, such as CMV, herpes simplex virus (HSV), and pneumocystis
pneumonia (37).
On radiographs, diffuse pneumonia appears as patchy or diffuse opacification. Areas of
air-space disease or reticular opacity may or may not be present. Influenza pneumonia in a
normal, healthy host usually has a mild course. In the elderly or debilitated patient, infection
can be fulminant and potentially fatal within a matter of days. Influenza pneumonia initially
appears on chest CT as diffuse bilateral reticulonodular areas, 1 to 2 cm in diameter, and
patchy ground-glass opacities. There may be small centrilobular nodules representing alveolar
hemorrhage. Over the course of days to weeks, depending on the condition of the patient,
diffuse consolidation may develop. Pleural effusions are rarely demonstrated. In a healthy
host, the findings should resolve within approximately three weeks (37,43).
Herpes simplex virus is a rare entity, occurring primarily in the immunocompromised or
those with airway trauma, such as the chronically intubated. Infection occurs either via
aspiration, via extension from oropharyngeal infection, or hematogenously in cases of sepsis.
Figure 25 CT scan of the chest demonstrates
two cavitary lesions in the left lung apex
containing soft-tissue material with lucent
areas and a surrounding crescent of air (“air
crescent” sign) compatible with aspergillomas.
There is also tracheal dilatation and preexistent
bronchiectasis as well as architectural distortion
of the upper lobes.Figure 26 CT scan of the chest in a 39-year-
old female with pulmonary tuberculosis demon-
strates left upper lobe consolidation along the
left major fissure with areas of cavitation. Addi-
tional opacities are seen diffusely in both lungs,
some of which demonstrate a “tree-in-bud”
configuration.Radiology of Infectious Diseases and Their Mimics in Critical Care 97