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. In the subgroup of patients who also had a chest radiograph, US demonstrated sensitivity and specificity of 81.4% and 94.2%, respectively, versus 64.3% and 90% for chest radiographs. The increased sensitivity of US implies additional value of US in cases in which the initial chest radiograph is discordant with clinical suspicion; however, 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. Given the difficulty of obtaining an accurate history and physical examination as well as the high incidence of PNA in patients with organic brain disease, US is a reasonable alternative to empiric treatment with antibiotics in the setting of a negative or equivocal initial chest radiograph. The ability of the patient to tolerate an US examination, presence of an adequate acoustic window, and the limited ability of US to detect all but peripheral PNAs would be additional considerations. MRI Chest Syrjala et al [14] compared the sensitivity and specificity of noncontrast MRI (respiratory-triggered T2 fast spin- echo) to chest radiographs using CT as a gold standard. The patient population consisted of immunocompetent adult ambulatory outpatients with ARI who were febrile and symptomatic for <7 days. CT detected 32 cases of PNA out of 77 prospectively enrolled patients. MRI detected 30/32 cases (sensitivity 94%) with no false-positives (specificity 98%), whereas chest radiographs only detected 23 cases (sensitivity 72%) and gave 4 false-positive results (specificity 91%). These data suggest a potential role for MRI in detecting PNA in situations where initial chest radiographs findings are negative or equivocal; however, the sensitivity of CT appears to be slightly superior to that of MRI.
Acute Respiratory Illness in Immunocompetent Patients. 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. In the subgroup of patients who also had a chest radiograph, US demonstrated sensitivity and specificity of 81.4% and 94.2%, respectively, versus 64.3% and 90% for chest radiographs. The increased sensitivity of US implies additional value of US in cases in which the initial chest radiograph is discordant with clinical suspicion; however, 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. Given the difficulty of obtaining an accurate history and physical examination as well as the high incidence of PNA in patients with organic brain disease, US is a reasonable alternative to empiric treatment with antibiotics in the setting of a negative or equivocal initial chest radiograph. The ability of the patient to tolerate an US examination, presence of an adequate acoustic window, and the limited ability of US to detect all but peripheral PNAs would be additional considerations. MRI Chest Syrjala et al [14] compared the sensitivity and specificity of noncontrast MRI (respiratory-triggered T2 fast spin- echo) to chest radiographs using CT as a gold standard. The patient population consisted of immunocompetent adult ambulatory outpatients with ARI who were febrile and symptomatic for <7 days. CT detected 32 cases of PNA out of 77 prospectively enrolled patients. MRI detected 30/32 cases (sensitivity 94%) with no false-positives (specificity 98%), whereas chest radiographs only detected 23 cases (sensitivity 72%) and gave 4 false-positive results (specificity 91%). These data suggest a potential role for MRI in detecting PNA in situations where initial chest radiographs findings are negative or equivocal; however, the sensitivity of CT appears to be slightly superior to that of MRI.