Chest imaging in immunosuppressed patients

• Bacterial pneumonias have similar radiographic patterns in immunocompetent and immunosuppressed patients. Chest radiographs and CT show consolidation, which may be focal (segmental or lobar), patchy or diffuse. • Tuberculosis in immunocompetent patients most frequently manifests as the reactivation (secondary) pattern, whereas immunosuppressed patients present the primary pattern of the disease. • If a neutropenic febrile patient presents with pulmonary nodules or consolidation surrounded by ground-glass opacities (“halo sign”), angioinvasive fungal infection must be the first diagnosis. • Pneumocystis jiroveci pneumonia should be the main diagnosis when ground-glass attenuation is seen in patients with human immunodeficiency virus with CD4+ <200 cells per cubic millimetre. • High-resolution CT features in viral infections are similar and show small poorly defined centrilobular nodules and consolidation foci and/or ground-glass attenuation with peribronchial distribution, and are multifocal and often bilateral. The immunosuppressed patient is at great risk for developing infectious and non-infectious complications. The lungs are frequently involved with these complications, which are responsible for higher morbidity and mortality in these patients compared with the general population. Infections are the main complication in this group, because they are susceptible to infections by organisms that are generally non-virulent in immunocompetent individuals, the kind of infection is related to the type of immune system dysfunction: cellular immunity abnormalities, humoural immunity abnormalities, neutrophil dysfunction or neutropenia. This article discusses the main imaging aspects of the most important infections in immunocompromised patients: bacterial, mycobacterial, fungal and viral. The main non-infectious complications in these patients and their imaging features are also shown, with special attention to pulmonary oedema, pulmonary haemorrhage, drug-induced injury, idiopathic pneumonia syndrome, bronchiolitis obliterans and some acquired immunodeficiency syndrome-related neoplasms and neoplastic-like conditions. Infections represent 75% of these complications, whereas non-infectious processes are responsible for 25% of the pulmonary problems in immunocompromised patients. Early diagnosis helps in reducing morbidity and mortality, and imaging studies play a major role in identifying the probable diagnosis, allowing targeted treatment even before microbiological culture would be available for confirming the diagnosis of a specific germ. CT can detect pulmonary lesions earlier than chest radiographs, being the modality of choice in these patients. Therefore, CT scan should be performed early in the course of disease, even when chest radiographs are normal.