[Imaging in respiratory infections].

The conventional X‑ray image is the method of choice for suspected pneumonia. Computed tomography (CT) is indicated for treatment refractory or recurrent infiltrates, difficult differential diagnostics, suspected complications and in immunocompromised patients. Thoracic sonography can be used as an alternative method for initial diagnostics and in the intensive care unit to monitor progress. In addition to the detection of infiltrates the radiological classification can help to limit the pathogen spectrum. Radiologically, three forms of pneumonia can principally be differentiated: lobar pneumonia, bronchopneumonia and interstitial pneumonia. Furthermore, there are special forms of pneumonia with certain pathogens, such as aspergilloma, invasive mycosis, postprimary tuberculosis and nontuberculous mycobacteriosis or in a specific clinical context, such as aspiration pneumonia, postinfarction pneumonia, retention pneumonia and septic emboli. The most frequent complications of pneumonia are lung abscesses and pleural empyema. Both can sometimes but not always be seen in the X‑ray image. If clinically suspected the indications for CT should be generously applied. Certain pre-existing diseases, such as immunodeficiency or structural alterations of the lungs can predispose to pulmonary infections, frequently with unusual pathogens or manifestation forms and must be taken into account in the diagnostics.