This can be remembered by the 4 'S': straight line dullness, shifting dullness, splash, sound of coin.
Diagnosis can be via CXR. CT is better for outlining borders of air-fluid levels, however, CT has a greater radiation exposure.
Ultrasound imaging has also proven to be a useful tool for hydropneumothorax diagnoses by looking for the absence of the characteristic "curtain sign" usually seen in ultrasound images at the base of healthy lungs.2
Treatment includes intercostal drainage (ICD) of fluid and air and treatment of underlying conditions.
Clarke, Christopher; Dux, Anthony (2017). Chest X-rays for Medical Students. John Wiley & Sons. p. 82. ISBN 9781119426721. Retrieved 6 November 2017. 9781119426721 ↩
Targhetta, Rémi; Bourgeois, Jean-Marie; Chavagneux, Roseline; Marty-Double, Christiane; Balmes, Pierre (1992-04-01). "Ultrasonographic Approach to Diagnosing Hydropneumothorax". Chest. 101 (4): 931–934. doi:10.1378/chest.101.4.931. ISSN 0012-3692. https://www.sciencedirect.com/science/article/abs/pii/S0012369216327040?casa_token=dzKB5EIxmOYAAAAA:9ql5J-ExM4ueaLglvVarQPCpwGpcEfMMwm4AELnUoxOUCsR7pZhFKUbJSj3kuULpPaKilPVWqd8 ↩