This post is part of the PEMBlog series on Community Acquired Pneumonia and is focused on imaging studies.

Before we begin know that per the 2011 Infectious Disease Society of America guidelines for community acquired pneumonia routine radiography is NOT REQUIRED to make the diagnosis. But, this post is about X-Rays (and more) and there are situations (many of them in fact) where radiographic studies can help you.

X-Rays

Again, if you think the child clinically has a pneumonia and does not have severe disease then you don’t need an X-Ray. At the very least obtain an anterior-posterior view. This is what your “portable” chest X-Ray gets you. However, the 2-view chest X-ray which includes AP and lateral views gives you a better look at the retrocardiac space.

When to get one?

The 2011 Infectious Diseases Society of America guidelines state that a patient with a clinical pneumonia that can be treated in the outpatient setting does not need an X-Ray. You should get an AP and lateral chest X-Ray in a patient with hypoxemia or respiratory distress, which includes the following;

What you’ll see?

Focal consolidation

This is what you will see most commonly, and is pretty specific for community acquired pneumonia. Of course focal areas of atelectasis can look like a consolidated pneumonia, and these areas on atelectasis are seen in 25% of bronchiolitis patients who had an X-Ray. But you’re not ordering an X-Ray in bronchiolitis right?  Overall, a lobar infiltrate is specific, but not sensitive for a bacterial pneumonia. Here are some specific examples of patterns you’ll see on plain radiographs:

Round pneumonia

Seen most commonly in young children (mean age 5 years) and classically associated with Streptococcus pneumoniae. The consolidation is focal and round, <3cm and more often posterior. They are sometimes completely circular, which is amazing! It is thought that this unique shape occurs in children because of the lack of inter-alveolar communication and collateral airways, which in adults leads to spread throughout the lobe. In young children you see more hyper-local spread, and the infection is well-contained within a circular space.

Case courtesy of A.Prof Frank Gaillard, Radiopaedia.org. From the case rID: 19638

Lobar consolidation

What most folks think of when they think of pneumonia. This is where one lobe or more have a focal area of opacity. Sometimes they can be subtle. Remember that X-rays are a 2D picture of 3D structures. Things of the same density (thick lung pus and the mediastinum) will appear to be the same opacity. That’s why the heart border can be hard to differentiate from the lung.

Case courtesy of Dr Jeremy Jones, Radiopaedia.org. From the case rID: 30652

Case courtesy of Dr Jeremy Jones, Radiopaedia.org. From the case rID: 30652

Pleural effusion

A pleural effusion is a complication of community acquired pneumonia and consists of fluid in the potential pleural space. You’ll generally see them inferiorly, and they will obscure the diaphragm.

A large pleural effusion from Pediatrics in Review

Necrotizing pneumonia

A very serious complication of community acquired pneumonia – often seen in pandemic influenza and in association with S. aureus infection. The following image is from a very sick child. Note the pneumatoceles (bracket), opacification in the right middle lobe (black arrow) and depression of the right hemidiaphragm (white arrow).

From http://www.cmaj.ca/content/183/2/215/F1.expansion.html

Other modalities

Ultrasound & Computed Tomography

These are most useful when you are trying to identify a pleural effusion that is not clear based on H&P and chest X-Ray. If a child is sick enough to need one of these to evaluate an effusion then it is safe to say that they need to be admitted.

Recent studies have shown that lung ultrasound may be helpful in making the diagnosis of uncomplicated pneumonia as well. A meta analysis from Pereda et al. showed a a sensitivity of 96% (95% CI 94%–97%) and specificity of 93% (95% CI 90%–96%), and positive and negative likelihood ratios were 15.3 (95% CI: 6.6–35.3) and 0.06 (95% CI: 0.03–0.11). The included studies did have a small sample size overall. So ultrasound is not ready to replace chest X-ray quite yet. Pneumonia when identified on ultrasound will have some of the following findings in this cool video courtesy of JAMA Pediatrics.

References

Bradley JS, Byington CL, Shah SS, et al. The management of community-acquired pneumonia in infants and children older than 3 months of age: clinical practice guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America. Clin Infect Dis 2011; 53:e25.

Harris M, Clark J, Coote N, et al. British Thoracic Society guidelines for the management of community acquired pneumonia in children: update 2011. Thorax 2011; 66 Suppl 2:ii1.