MRI Chest Our literature search failed to identify any data that suggest that MRI serves any significant role in the initial imaging of immunocompetent patients with a high pretest probability of PNA. The role of MRI for patients with a negative or equivocal initial chest radiograph is discussed in Variant 3. Variant 3: Acute respiratory illness in immunocompetent patients with positive physical examination, abnormal vital signs, organic brain disease, or other risk factors and negative or equivocal initial chest radiograph. Next imaging study. Radiography Chest There is no indication in the literature to suggest that repeat chest radiograph serves any significant role in imaging patients with a high pretest probability of PNA and a negative or equivocal initial chest radiograph. CT Chest There are several studies that assess the use of CT as a subsequent study in patients who have already had a chest radiograph. One of the larger reviews by Hayden et al [32] identified 97 of 1,057 ED patients with a diagnosis of PNA who had both a chest radiograph and CT. Within this selected group, 26 patients (27%) had PNA that was not detected with chest radiograph but was subsequently detected with CT. Maughan et al [33], in a retrospective review designed to evaluate the false-negative rate of chest radiographs in ED patients with PNA, identified 49 cases (11.4%) where PNA was diagnosed with CT, despite a normal chest radiograph. Haga et al [6] also demonstrated the improved ability of CT to assess the severity of PNA relative to chest radiographs. Bilateral PNA, as detected by CT, was associated with a higher degree of mortality. The presence of multilobar opacities, which is a minor criterion in the IDSA/ATS guidelines for intensive care unit admission, is best assessed with CT [4]. One of the more recent studies assessing the use of CT for ED patients with suspected PNA is Claessens et al [7], a prospective multicenter study that enrolled 319 patients.
Acute Respiratory Illness in Immunocompetent Patients. MRI Chest Our literature search failed to identify any data that suggest that MRI serves any significant role in the initial imaging of immunocompetent patients with a high pretest probability of PNA. The role of MRI for patients with a negative or equivocal initial chest radiograph is discussed in Variant 3. Variant 3: Acute respiratory illness in immunocompetent patients with positive physical examination, abnormal vital signs, organic brain disease, or other risk factors and negative or equivocal initial chest radiograph. Next imaging study. Radiography Chest There is no indication in the literature to suggest that repeat chest radiograph serves any significant role in imaging patients with a high pretest probability of PNA and a negative or equivocal initial chest radiograph. CT Chest There are several studies that assess the use of CT as a subsequent study in patients who have already had a chest radiograph. One of the larger reviews by Hayden et al [32] identified 97 of 1,057 ED patients with a diagnosis of PNA who had both a chest radiograph and CT. Within this selected group, 26 patients (27%) had PNA that was not detected with chest radiograph but was subsequently detected with CT. Maughan et al [33], in a retrospective review designed to evaluate the false-negative rate of chest radiographs in ED patients with PNA, identified 49 cases (11.4%) where PNA was diagnosed with CT, despite a normal chest radiograph. Haga et al [6] also demonstrated the improved ability of CT to assess the severity of PNA relative to chest radiographs. Bilateral PNA, as detected by CT, was associated with a higher degree of mortality. The presence of multilobar opacities, which is a minor criterion in the IDSA/ATS guidelines for intensive care unit admission, is best assessed with CT [4]. One of the more recent studies assessing the use of CT for ED patients with suspected PNA is Claessens et al [7], a prospective multicenter study that enrolled 319 patients.