On radiographs, the most common findings are patchy segmental or subsegmental areas of air-
space disease. CT demonstrates multifocal segmental and subsegmental areas of ground-glass
opacity with smaller areas of focal consolidation. Pleural effusion is commonly present with
herpes pneumonia (43).
CMV pneumonia is seen most often in transplant patients as well as AIDS patients. On
CT, the appearance may vary. Mixed alveolar and interstitial abnormalities; consolidation;
nodules; small, ill-defined centrilobular nodules; bronchial dilatation; and thickened
interlobular septa are all potential findings. (43,44)
Unlike the typical viral diffuse pneumonias, pneumocystis pneumonia is caused by the
fungusP. jiroveci, a common organism found in otherwise normal human lungs, but which in
the immunocompromised host may cause pneumonia. The radiographic appearance of
pneumocystis pneumonia varies widely. Chest radiographs are often completely normal early
in the infection. Fine reticular or ground-glass opacities, predominantly in the hilar regions,
may be seen on CT (Fig. 27). Progressive disease results in formation of confluent areas of air-
space opacification. Asymmetric or focal areas of interstitial disease are also highly suggestive
of pneumocystis pneumonia in the correct clinical context. Significant adenopathy and pleural
effusions are highly unusual, and their presence usually indicates an alternate diagnosis. Thin-
walled cysts or pneumatoceles can also be seen with pneumocystis pneumonia, as can
pneumothorax (25,38,43).
Mimics of Diffuse Bilateral Pneumonia
Congestive Heart Failure
Congestive changes occur in two phases: interstitial edema and alveolar flooding or edema.
With increased transmural arterial pressure, the earliest findings are loss of definition of
subsegmental and segmental vessels; enlargement of peribronchovascular spaces; and the
appearance of Kerley A, B, and C lines, reflecting fluid in the central connective septa,
peripheral septa, and interlobular septa, respectively. If allowed to progress, increasing
accumulation of fluid results in spillage into the alveolar spaces, which is exhibited by
confluent opacities primarily in the mid and lower lungs. A “bat’s wing” or “butterfly”
appearance is classic for CHF, although this is relatively rarely seen. A potentially helpful
differentiating feature from other causes of diffuse bilateral air-space opacities is the rapid time
frame in which these changes occur. CT findings can also be helpful for demonstrating
thickening of subpleural, septal, and bronchovascular structures, along with ground-glass
opacities with a gravitational anterior–posterior gradient. Common associated findings are
cardiomegaly, pulmonary venous distention, and pleural effusion (37,45).
Pulmonary Hemorrhage
Pulmonary hemorrhage may result from trauma, bleeding diathesis, infection, and auto-
immune causes. Radiographic findings include bilateral coalescent air-space opacities that
develop rapidly and that commonly improve rapidly with a time course of hours, as opposed
to days or weeks, such as with most cases of pneumonia (37).
Figure 27 CT scan of the chest demonstrates
emphysematous change with superimposed dif-
fuse ground-glass opacity in a 58-year-old
immunocompromised female with pneumocystis
pneumonia.98 Luongo et al.