Chest Radiograph vs. Computed Tomography Scan in the Evaluation for Pneumonia

Abstract

To determine, in an Emergency Department (ED) population, the incidence of pneumonia diagnosed on thoracic computed tomography (CT) in the setting of negative or non-diagnostic chest radiographs (CXR). This is a retrospective chart review of all ED visits of adult patients ultimately diagnosed with “pneumonia” in whom both CXR and CT were obtained. We note cases in which the CXR was either negative or non-diagnostic for pneumonia and the CT noted a definitive infiltrate consistent with pneumonia. Of the 1,057 patients diagnosed with pneumonia, both CXR and CT were performed in 97 cases. Of this group, there were 26 patients (27%), in whom the CXR was either negative or non-diagnostic, but the CT noted an infiltrate/consolidation consistent with pneumonia. In our retrospective review of ED patients, we find that in 27% of cases in which both a CXR and a CT scan were performed in the work-up of varied chief complaints, pneumonia was demonstrated on CT in the face of a negative or non-diagnostic CXR. This analysis demonstrates the need for further studies regarding the appropriate radiographic evaluation of pneumonia, particularly in high-risk patients.

Introduction

In the United States, there are over 5 million cases of community-acquired pneumonia (CAP) each year, with approximately 2 million requiring hospitalization; almost 50,000 deaths are attributed to CAP (sixth leading cause of death from infectious diseases). The estimated annual cost of treatment is over $20 billion (1).

Chest radiography is the usual standard for diagnosing pneumonia in the Emergency Department (ED), and virtually all studies looking at the diagnosis and disposition of patients have used plain chest X-ray study interpretation (by a Radiology attending) as the reference standard (2, 3). Further, the standard of care in the ED is to treat adult patients with radiographic evidence of an infiltrate with antibiotics, because this illness continues to have an overall high mortality (4). When patients with cough or fever have a normal lung examination and a negative chest X-ray study, “pneumonia” is ruled out and oftentimes “bronchitis” is diagnosed. The use of antibiotics to treat “bronchitis” in adults is discouraged (5). Our study was performed to assess the incidence of pneumonia diagnosed on thoracic computed tomography (CT) scan in the setting of negative or non-diagnostic chest radiographs (CXR).

Unfortunately, chest radiography, the most common imaging modality in the diagnosis of pneumonia, has been shown to be somewhat unreliable in the definitive diagnosis of pneumonia. Although the significance of this is unknown, there is a demonstrable superiority of thoracic CT scan over CXR in the diagnosis of pneumonia in particular patient populations. Studies have favorably compared CT scan vs. CXR in populations of immunocompetent children, neutropenic patients, and patients with human immunodeficiency virus (HIV) (6, 7, 8). At present, there have been no studies that specifically look at an ED population with regard to pneumonia evident on thoracic CT scan in the setting of a negative or non-diagnostic chest X-ray study.