Opaque hemithorax (whiteout): A literature review exploring its causes, potential use of thoracic ultrasound and the role of physiotherapy

Abstract

PURPOSE: Complete whitening of one half of the thorax on a chest radiograph (CXR) is termed an opaque hemithorax. It often indicates the presence of significant pathology resulting in respiratory compromise. There are numerous causes of an opaque hemithorax, but these are not immediately apparent on CXR. Thoracic ultrasound (TUS) has a higher accuracy to differentiate between opacities on CXR and may help to correctly identify underlying pathologies. The purpose of this literature review is to report the causes of an opaque hemithorax, identify how TUS can assist diagnosis and explore the role physiotherapy has opaque hemithorax management. METHODS: A systematic search was conducted (PubMed, Medline, Embase, CINAHL, AMED and BNI) up until March 2018. Inclusion: Adults. Primary research reporting a complete opaque hemithorax on CXR. RESULTS: 1117 papers were identified in search. Following inclusion and exclusion criteria: 58 papers were selected. 54 papers were case reports and four were observational studies. The causes of the opaque hemithorax were collated and divided into 16 categories. Eight studies included the use of TUS to differentiate the cause of the opaque hemithorax. Two studies reported the involvement of physiotherapy in opaque hemithorax. CONCLUSIONS: Numerous pathologies can cause an opaque hemithorax on CXR making differential diagnosis difficult. Even when mediastinal shift is present it does not appear to be a reliable way to identify the underlying cause. Thoracic ultrasound has the potential to much more accurately differentiate between pathologies. This would assist physiotherapists to identify patients amenable to physiotherapy treatment techniques.