Diagnoses of Consequence
The differential diagnosis of pneumonia includes both infectious
and noninfectious conditions, as well as extrapulmonary disorders
that may mimic or complicate lower respiratory tract infection (Table 121-2). This is especially important
in pediatric patients, who may have undiagnosed congenital anomalies.
Table 121-2 Differential
Diagnosis of Pneumonia |Favorite Table|Download (.pdf)
Table 121-2 Differential
Diagnosis of Pneumonia
|Infectious Causes||Noninfectious Causes||Extrapulmonary Causes|
|Upper respiratory tract infection (“cold”),
otitis media||Foreign-body aspiration||Sepsis|
|Inhalation pneumonitis (e.g., hydrocarbon
inhalation, chronic gastroesophageal reflux disease)||Cardiac anomalies (cyanotic heart disease,
congestive heart failure, myocarditis)|
|Intoxication (e.g., salicylate poisoning, carbon monoxide
exposure)||Endocrinopathies (e.g., diabetic ketoacidosis)|
|Congenital disorders (e.g., cystic fibrosis, sickle cell
disease with chest crisis)||Neuromuscular disorders|
|Anatomic abnormalities (e.g., congenital lobar
emphysema, pulmonary sequestration, tracheoesophageal fistula, congenital
cystic adenomatous malformation)||Inborn errors of metabolism|
|GI emergencies (e.g., appendicitis with grunting)|
For children with respiratory distress but no fever,
a search for causes other than pneumonia is required. Congenital
heart disease may present with cyanosis, quiet tachypnea, or signs
of respiratory distress related to congestive heart failure (see Chapter 122A, Pediatric Heart Disease: Congenital
Heart Defects, and Chapter 122B, Pediatric
Heart Disease: Acquired Heart Disease). Respiratory distress
and Kussmaul breathing should arouse suspicion of diabetic ketoacidosis
or other metabolic disease. Toddlers are particularly at risk for
foreign-body aspiration and ingestion of toxins. Adolescents may
intentionally or unintentionally take drug overdoses that speed
or slow breathing.
Because the results of most laboratory investigations are not
known in the ED, tests are usually initiated to guide future treatment.
Rapid bedside tests for specific viral infections are an exception. Nasopharyngeal assays
for RSV, influenza, and human metapneumovirus can be valuable, because
they are quick and specific, and results may obviate the need for
additional invasive testing, exposure to x-rays, or antibiotic therapy. Imaging
may also be deferred and antibiotics withheld for children who do
not have a toxic appearance and who have clinical bronchiolitis,
especially those with a positive nasopharyngeal swab finding.3
Bacterial cultures of nasopharyngeal samples are generally not helpful, because
results are delayed and oral flora correspond poorly with the organisms
causing disease in the lung. The majority of newer serologic and polymerase
chain reaction techniques to detect organisms such as H.
influenzae or C. pneumoniae have not been
validated in children and have produced variable results.3,5 In
patients with a toxic appearance and those destined for admission,
many clinicians draw blood samples for culture to help narrow the
spectrum of treatment in hospital, although the yield of such cultures
is low and routine use is not necessary.
When TB is suspected, obtaining induced sputum samples from older children
or gastric aspirates from infants for microscopy and confirmatory
culture is helpful.28 These tests require equipment
and expertise beyond the scope of the ED.
Along with the history and physical examination, the plain radiograph (“chest
x-ray”) is often used to diagnose pediatric pneumonia.
Used appropriately, it can help to distinguish between pneumonia
and other types of respiratory infection, and between respiratory
and nonrespiratory (e.g., cardiac) sources of symptoms. This section
discusses when to order a chest radiograph and how to recognize
some common and unusual findings.
When and Why
to Order a Radiograph
A chest radiograph should be ordered when clinically indicated
and when the results are likely to alter diagnosis, treatment, or
outcome. The chest radiograph is not the gold standard of diagnosis,
because it is neither 100% sensitive nor 100% specific.29 In
the ED, a small number of children may present with clinical signs
and symptoms of pneumonia before there are radiographic changes,
which leads to false negative diagnoses. More commonly, an image taken
with poor inspiration or rotation may give the false impression
of a pulmonary infiltrate (Figures 121-1 and 121-2), which leads to unnecessary treatment
with antibiotics. Clinicians who are unaccustomed to ordering and
interpreting pediatric radiographs may find this especially challenging.
Poor inspiration results in the appearance of pulmonary
infiltrates and cardiomegaly in this normal 4-month-old. (Courtesy of
BC Children’s Hospital, Vancouver, BC, Canada.)
The same child as in Figure 121-1,
with adequate inspiration. Note that persistent rotation (see clavicles)
causes a false difference in left and right lung density. (Courtesy
of BC Children’s Hospital, Vancouver, BC, Canada.)
Guidelines on the use of routine chest radiography are contradictory.3,30 There
are risks and benefits to ordering chest radiograph in febrile infants.
Benefits include diagnosis or confirmation of pneumonia and occasionally
the discovery of a significant congenital abnormality. Risks and
disadvantages include cost, delay, repeated exposure to ionizing
radiation, and overdiagnosis of bacterial pneumonia.31 Young
children with straightforward viral bronchiolitis may still show
radiographic areas of atelectasis or patchy collapse, tempting emergency
physicians to initiate antibiotic therapy.32
Of note, a randomized trial involving children in Cape Town,
South Africa, found that chest radiography had
no statistically significant impact on clinical outcome in ambulatory children
with lower respiratory tract infections, and the authors recommended
against its routine use in children >2 months of age.33 Thus some
guidelines state that imaging should not be performed
routinely in children with mild, uncomplicated acute lower respiratory
tract infections.3 Most of these studies and guidelines
involved the review of data obtained in ambulatory care settings
in which children with prolonged cough, severe symptoms, and other “red
flag” features were excluded, so these recommendations
must be applied to the ED with caution. If imaging is deferred,
or radiographs are read as “negative” for pneumonia, follow-up
at 24 to 48 hours should be arranged.
Although routine radiographs are not usually necessary, some
potential indications for chest radiography include the following12,30,34,35:
1. Age of 0 to 3 months, as part of a workup for sepsis
2. Age of <5 years in a child with a temperature of >39°C (102.2°F),
white blood cell count of ≥20,000/mm3, and no clear
source of infection
3. Ambiguous clinical findings
4. Suspicion of a complication, such as pleural effusion
5. Pneumonia that is prolonged or unresponsive to
6. Suspicion of foreign-body aspiration
7. Suspected congenital lung malformation (e.g., sequestration or
congenital cystic adenomatous malformation)
8. Follow-up of “round pneumonia” to ensure resolution
and exclude an underlying mass
Note that the child with a toxic appearance
who has respiratory findings should always undergo chest radiography,
and some infants may merit imaging as part of a workup for sepsis,
even if no clinical signs are present.
Numerous reviews of the literature have concluded that the chest
radiograph cannot reliably distinguish between
bacterial and viral causes.36,37 Practically speaking,
most children presenting to the ED with clinical symptoms of pneumonia
and obvious lobar or segmental consolidation receive antibiotics.
Tips on Interpreting
the Pediatric Chest Radiograph
Physicians accustomed to reviewing adult radiographs may find
some elements of the pediatric image confusing, and a systematic
and age-appropriate approach to the pediatric chest radiograph is
helpful. An exhaustive list of potential abnormalities is neither
possible nor necessary, but the following discussion and images
should help the emergency physician to develop such an approach
and recognize significant pathology.
The chest of a neonate (<1 month of age) has a more pyramidal
or trapezoidal shape than the long, rectangular form of the adult.
The cardiac silhouette may occupy up to 60% or 65% of
the chest width on the posterior-anterior view and still be considered
normal. In infants, bronchial branching may be seen beyond the level
of the carina, giving the false impression of pathologic air bronchograms.
The normal thymus can be seen as a large, dense, anterior mediastinal “sail” until
involution occurs around age 6. A normal thymus can often be recognized
by the sharp inferior edge of its silhouette and occasionally by
a “wave” or “sail” sign at the
lateral edge, where the adjacent ribs indent this soft, solid organ.
Occasionally the thymus may be confused with a lobar pneumonia, mediastinal
mass, or hilar lymphadenopathy (Figure 121-3). A lateral view can help to
confirm the anterior location of the thymus. (Figure 121-4). A silhouette that extends
behind the heart shadow or posterior to the vertical lucency of
the trachea should be investigated.
Arrows indicate a normal thymus. Rotation, apparent from
the location of the heart, trachea, and clavicles, makes this thymus appear
to be far right of midline. (Courtesy of BC Children’s
Hospital, Vancouver, BC, Canada.)
Lateral view confirms thymic density fully confined to the
anterior mediastinum (arrows). (Courtesy of BC
Children’s Hospital, Vancouver, BC, Canada.)
Occasionally parents may bring a very young newborn to the ED
because of real or perceived breathing difficulties. Noninfectious
causes of tachypnea and respiratory distress in the first few days of
life include “wet lung” or transient tachypnea
of the newborn, and chemical pneumonitis from meconium aspiration.
The former may cause increased vascular markings, linear interstitial
opacities, and even pleural effusions on radiographs due to interstitial
edema. Meconium aspiration can block small airways, leading to hyperinflation
and bilateral air space opacities on plain radiographs. A good birth
history, physical examination, and chest radiograph may help to
distinguish some of these noninfectious causes from infectious ones.
(Signs of interstitial opacities or edema should prompt observation
and/or consultation.) Premature babies, intensive care “graduates,” and
even healthy, term newborns are still at increased risk for bacterial
pneumonias. Neonatal pneumonia is always treated on an inpatient
basis with parenteral antibiotics.
In addition to contracting pneumonia from the infectious causes
noted earlier in Table 121-1, toddlers
are susceptible to choking and foreign-body aspiration from objects
they can reach. These may include organic materials (e.g., food)
or inorganic objects (coins, buttons, batteries), as well as volatile
toxins such as cleaning products, gasoline, or other hydrocarbons.
Retained foreign bodies can lead to respiratory distress and febrile
aspiration pneumonia. Careful review of the chest radiograph is
critical, and consultation may be necessary if a foreign body is
not seen but still suspected (e.g., air trapping or segmental collapse
past an obstructed bronchus). By contrast, inhaled hydrocarbons
and irritants may yield a pneumonitis with patchy lower air space
opacities, and even pneumatoceles, if the presentation is delayed.
Children symptomatic from an inhalation pneumonitis require admission
and/or close follow-up. Tachypnea, respiratory distress,
and fever with no radiographic findings may suggest
a toxic cause such as salicylate ingestion or a metabolic disorder,
including diabetic ketoacidosis.
By school age, the radiographic signs of chest infection in children
become more similar to the typical findings in adults. There may
be obvious lobar consolidation or patchy, multifocal findings. Younger
children can also present with “round pneumonia” (Figure 121-5), a sharply defined consolidation
often found in the posterior lower lobe, classically from pneumococcal
infection. Children with round pneumonias should have radiographic
follow-up to confirm resolution and ensure that this finding is
not actually a mass. Cavitation and pleural effusions should arouse
suspicion of infection with S. aureus or S.
pneumoniae, particularly penicillin-resistant pneumococcus
Anterior-posterior (A) and lateral views
(B) shows lower lobe consolidation (arrows).
(Courtesy of BC Children’s Hospital, Vancouver, BC, Canada.)
Complicated left-sided pneumonia. Note the pleural effusion
(white arrows) and cavitation (black arrows).
(Courtesy of BC Children’s Hospital, Vancouver, BC, Canada.)
Patchy atelectasis and air space consolidation
in the dependent zones of the lung should raise suspicion of aspiration
pneumonia or pneumonitis. Recurrent aspiration pneumonias may occur
in children with chronic gastroesophageal reflux disease, tracheoesophageal
fistula, developmental delay, immobility, or neuromuscular disorders.