Imaging Diagnosis of ARDS: How Can We Know the Severity and Prognosis from the Lung Imaging?

Abstract

Acute respiratory distress syndrome (ARDS) is a critical syndrome and its mortality remains high. Based on Berlin criteria for ARDS, chest imaging plays an important role. For clinicians, evaluation of disease severity and prediction of prognosis are quite helpful for management of ARDS. Chest radiograph is a simple test and first stage of diagnosis for ARDS. Findings of chest radiograph are often affected by patient status, positive pressure ventilation, and stage of ARDS itself. Therefore, integration of clinical condition such as vital sign and ratio of partial pressure of oxygen and fraction of inspired oxygen (P/F ratio) is important. Most important differential diagnosis is congestive heart failure (CHF). Therefore, evaluation of lung water distribution is important. Most robust point of chest radiograph is detection of volume loss comparison with previous film. Chest high-resolution computed tomography (HRCT) is the most useful imaging tool for ARDS. HRCT can distinguish direct injury such as pneumonia, aspiration from indirect injury such as sepsis, burn. Direct injury often shows asymmetric distribution such as unilateral predominant consolidation with air bronchogram. On the other hand, indirect injury more often demonstrates gravity dependent consolidation with subtle ventral ground-glass opacity (GGO). In viewpoint of severity of ARDS, severe ARDS patients show more extensive shadow compared to mild or moderate ARDS. In prediction of prognosis, ARDS have three pathological stages which consist of exudative, fibroproliferative, and fibrotic phase. In chest HRCT, extent of fibrotic shadow such as reticulation and traction bronchiectasis and volume loss are crucial findings which are associated with poor prognosis.