High-resolution CT findings of idiopathic pneumonia syndrome after haematopoietic stem cell transplantation: based on the updated concept of idiopathic pneumonia syndrome by the American Thoracic Society in 2011

Idiopathic pneumonia syndrome (IPS) is an acute lung dysfunction of non-infectious aetiology and a severe complication following haematopoietic stem cell transplantation (HSCT). Recently, the American Thoracic Society (ATS) updated the concept of IPS and extended the concept to a wider range; it defined IPS as “an idiopathic syndrome of pneumopathy after HSCT, with evidence of widespread alveolar injury and in which infectious aetiologies and cardiac dysfunction, acute renal failure, or iatrogenic fluid overload have been excluded.” The ATS also categorised the presumed site of primary tissue injury into three patterns (pulmonary parenchyma, vascular endothelium, and airway epithelium), each of which has several entities. Since the therapeutic strategies for IPS are clearly different from those of infectious diseases, and therapeutic delay causes a poor prognosis, radiologists should be aware of some characteristic HRCT findings of IPS, which includes a wide spectrum of entities. In this article, the characteristic HRCT findings of these entities, including acute interstitial pneumonia/acute respiratory distress syndrome, eosinophilic pneumonia, non-cardiogenic capillary leak syndrome, diffuse alveolar haemorrhage, transfusion-related acute lung injury, organising pneumonia, and bronchiolitis obliterans syndrome, are shown.