CT provides enhanced characterization of pulmonary parenchymal abnormalities that are due to its superior spatial resolution and cross-sectional display of findings. Consequently, certain infections can be identified on CT with a higher degree of confidence than on radiographs ARI in Immunocompromised Patients [15-17]. Common CT patterns of disease in patients with ARI include pulmonary nodules, tree-in-bud pattern, lung consolidation, and ground-glass opacities [4]. These patterns have been described in the literature to represent the appearances of a number of pulmonary infections in the immunocompromised host, including P. jirovecii [8,15,16], invasive pulmonary aspergillosis [15,17-20], mucormycosis [21,22], candidiasis [22,23], cytomegalovirus pneumonia [15,24,25], human metapneumovirus [26-28], and mycobacterial pneumonias [29- 32]. CT shows the detailed morphology of parenchymal opacities, as well as the pattern and distribution of disease. For example, in febrile patients having undergone recent stem cell transplantation, the ability of CT to detect halos of ground-glass opacity around pulmonary nodules is helpful in making the early presumptive diagnosis of invasive aspergillosis, thus prompting initiation of empiric antifungal therapy with improved prognosis [17,19]. Furthermore, CT may show the presence of infection complications, such as empyema or abscess that may not be visible on radiographs. MRI Chest CT is preferable to MRI in immunocompromised patients with ARI who have chest radiographs showing multiple, diffuse, or confluent opacities. CT remains superior to MRI in the detection and characterization of pulmonary parenchymal infection [9,10]. However, when the aerated parenchyma is replaced by consolidation, nodules, or masses, MRI can be considered as an alternative imaging modality, albeit less sensitive. Recent studies have shown that MRI can be used for the diagnosis of pulmonary infection [9,12,33].
Acute Respiratory Illness in Immunocompromised Patients. CT provides enhanced characterization of pulmonary parenchymal abnormalities that are due to its superior spatial resolution and cross-sectional display of findings. Consequently, certain infections can be identified on CT with a higher degree of confidence than on radiographs ARI in Immunocompromised Patients [15-17]. Common CT patterns of disease in patients with ARI include pulmonary nodules, tree-in-bud pattern, lung consolidation, and ground-glass opacities [4]. These patterns have been described in the literature to represent the appearances of a number of pulmonary infections in the immunocompromised host, including P. jirovecii [8,15,16], invasive pulmonary aspergillosis [15,17-20], mucormycosis [21,22], candidiasis [22,23], cytomegalovirus pneumonia [15,24,25], human metapneumovirus [26-28], and mycobacterial pneumonias [29- 32]. CT shows the detailed morphology of parenchymal opacities, as well as the pattern and distribution of disease. For example, in febrile patients having undergone recent stem cell transplantation, the ability of CT to detect halos of ground-glass opacity around pulmonary nodules is helpful in making the early presumptive diagnosis of invasive aspergillosis, thus prompting initiation of empiric antifungal therapy with improved prognosis [17,19]. Furthermore, CT may show the presence of infection complications, such as empyema or abscess that may not be visible on radiographs. MRI Chest CT is preferable to MRI in immunocompromised patients with ARI who have chest radiographs showing multiple, diffuse, or confluent opacities. CT remains superior to MRI in the detection and characterization of pulmonary parenchymal infection [9,10]. However, when the aerated parenchyma is replaced by consolidation, nodules, or masses, MRI can be considered as an alternative imaging modality, albeit less sensitive. Recent studies have shown that MRI can be used for the diagnosis of pulmonary infection [9,12,33].