CT Chest The major advantage of CT in the setting of ARI is its increased sensitivity relative to chest radiographs for the diagnosis of PNA. In comparative studies in which patients with PNA received both CT and chest radiograph, the rate of PNA missed by chest radiographs but detected by CT has been highly variable, ranging from 9.4% [6] to 56.5% [5]. CT has also been shown to be more specific than chest radiographs for the diagnosis of PNA [5,7]. US Chest There is a growing body of literature suggesting that bedside lung ultrasound (US) can be a useful tool in the diagnosis and management of PNA [8-12]. Nazerian et al [10] evaluated the accuracy of US relative to CT on 285 patients who had at least one respiratory complaint for which the ED physician ordered a CT. CT was considered positive if at least one typical consolidation was detected. US identified at least one consolidation in 81 patients versus 87 for CT. Relative to CT; US had a sensitivity of 82.8% and a specificity of 95.5%. While this study demonstrates impressive performance of US for detecting pulmonary consolidation, the study was limited by the fact that patients were enrolled based on whether or not they had a CT ordered rather than clinical suspicion of PNA. US is of limited value in patients with subcutaneous emphysema, in the setting of obesity/thick chest wall, and in patients with limited chest wall access related to bandages, prosthetic material, and skin disorders [13]. In addition, US has difficulty identifying PNAs that are not adjacent to the pleura. This limits its effectiveness for detecting more central infections, especially when there is aerated lung intervening between the transducer and the PNA [8,10,11]. MRI Chest Our literature search identified one recently published article evaluating the use of MRI in the setting of ARI in immunocompetent adult patients [14]. The study suggests a sensitivity for PNA that approaches that of CT.
Acute Respiratory Illness in Immunocompetent Patients. CT Chest The major advantage of CT in the setting of ARI is its increased sensitivity relative to chest radiographs for the diagnosis of PNA. In comparative studies in which patients with PNA received both CT and chest radiograph, the rate of PNA missed by chest radiographs but detected by CT has been highly variable, ranging from 9.4% [6] to 56.5% [5]. CT has also been shown to be more specific than chest radiographs for the diagnosis of PNA [5,7]. US Chest There is a growing body of literature suggesting that bedside lung ultrasound (US) can be a useful tool in the diagnosis and management of PNA [8-12]. Nazerian et al [10] evaluated the accuracy of US relative to CT on 285 patients who had at least one respiratory complaint for which the ED physician ordered a CT. CT was considered positive if at least one typical consolidation was detected. US identified at least one consolidation in 81 patients versus 87 for CT. Relative to CT; US had a sensitivity of 82.8% and a specificity of 95.5%. While this study demonstrates impressive performance of US for detecting pulmonary consolidation, the study was limited by the fact that patients were enrolled based on whether or not they had a CT ordered rather than clinical suspicion of PNA. US is of limited value in patients with subcutaneous emphysema, in the setting of obesity/thick chest wall, and in patients with limited chest wall access related to bandages, prosthetic material, and skin disorders [13]. In addition, US has difficulty identifying PNAs that are not adjacent to the pleura. This limits its effectiveness for detecting more central infections, especially when there is aerated lung intervening between the transducer and the PNA [8,10,11]. MRI Chest Our literature search identified one recently published article evaluating the use of MRI in the setting of ARI in immunocompetent adult patients [14]. The study suggests a sensitivity for PNA that approaches that of CT.