Viral Pneumonias (General):
Viruses can result in several forms of lower respiratory tract
infection including tracheobronchitis, bronchiolitis, and pneumonia
. Adenovirus has the greatest effect in the terminal bronchioles .
A viral etiology is the most common cause of pneumonia in children
the age of 5 years. Pathogens include: Respiratory syncytial virus
parainfluenza, adenovirus, influenza, enterovirus, and rhinovirus.
include: Subsequent bacterial pneumonia; Bronchiectasis; and
Syndrome. The infection primarily affects the AIRWAYS (not the alveoli)
therefore will see changes secondary to airblock.
In adults viral pneumonias are usually gradual in onset, have
non-pulmonary symptoms, and typically only produce mild elevations in
white blood cell count. RSV and parainfluenza virus typically produce
upper airway infections or bronchitis (characterized by evidence of
airway inflammation with tree-in-bud
opacities, bronchial wall thickening, and peribronchiolar
consolidaiton) . Rhinovirus predominantly
only the upper respiratory tract. Adenovirus infection typically
prresents as a multifocal pneumonia pattern with areas of ground-glass
opacity or consolidation without airway abnormalities .
Influenza A is the most important respiratory viral illness with
more than 35,000 deaths and 200,000 hospitalizations annually .
Symptoms include rapid onset of high fever, myalgias, headache,
lethargy, sore throat, and cough .
Avian flu is caused by the H5N1 subtype of influenza A virus and
approximately 90% of infections have occurred in patients 40 years old
or younger . The fatality rate exceeds 60% .
Measles virus is a highly contagious infection with an incubation
time of almost 2 weeks . It can result in a fatal pneumonia in
immunocompromised and debilitated patients .
In children, the CXR characteristically demonstrates HYPERINFLATION
a reticular or airspace pattern. The infection is more commonly
as opposed to lobar. Other findings include perihilar linear densities
with loss of hilar and vascular sharpness, patchy atelectasis, and
wall thickening (peribronchial cuffing). Adenopathy (3%) and effusion
In adults, viral infections commonly produce a diffuse, fine
pattern. Bronchial wall thickening is also common. Severe infection can
result in air space opacities- typically patchy in distribution.
that develop a pneumonia secondary to an influenza infection
a rapidly progressive bilateral pneumonia or patchy bronchopneumonia.
with Staphylococcus should be suspected if cavitation develops.
On HRCT, bronchial wall thickening, septal prominence, patchy areas
of heterogeneous/ground glass attenuation, centrilobular ground glass
nodules, airspace consolidation, and/or small branching nodular
in the lung periphery (tree-in-bud- indicative of bronchiolar
can all be seen .
(1) Radiology 2011; Franquet T. Imaging of pulmonary viral pneumonia.
(2) AJR 2011; Miller WT, et al. CT of viral lower repiratory tract
infections in adults: comparison among viral organisms and between
viral and bacterial infections. 197: 1088-1095