Hydropneumothorax is defined as the presence of both air and fluid within the pleural space. An upright chest x-ray will show air fluid levels. The horizontal fluid level is usually well defined and extends across the whole length of one of the hemithorax. Signs and symptoms
This can be remembered by the 4 S:
straight line dullness,
shifting dullness,
splash,
sound of coin. Causes
Iatrogenic: Introduction of air during pleural fluid aspiration in effusion
Presence of a gas-forming organism
Thoracic trauma

Diagnosis
Diagnosis can be via CXR. CT is better to outline borders of air fluid levels, however, CT has a greater radiation exposure. Treatment
Treatment includes ICD (intercostal drainage) of fluid and air and treatment of underlying conditions. References


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Lesions
Primary lesions
Macule: A macule is a change in surface color, without elevation or depression, so nonpalpable, well or ill-defined, variously sized, but generally considered less than either 5 or 10 mm in diameter at the widest point. Patch: A patch is a large macule equal to or greater than either 5 or 10 mm across, depending on ones definition of a macule. Patches may have some subtle surface change, such as a fine scale or wrinkling, but although the consistency of the surface is changed, the lesion itself is not palpable. Papule: A papule is a circumscribed, solid elevation of skin, varying in size from less than either 5 or 10 mm in diameter at the widest point. Plaque: A plaque has been described as a broad papule, or confluence of papules equal to or greater than 10 mm, or alternatively as an elevated, plateau-like lesion that is greater in its diameter than in its depth. Nodule: A nodule is morphologically similar to a papule in that it is also a palpable spherical lesion less than 10 mm in diameter. However, it is differentiated by being centered deeper in the dermis or subcutis. Tumor: Similar to a nodule, but it is larger than 10 mm in diameter. Vesicle: A vesicle is a small blister, a circumscribed, epidermal elevation generally considered less than either 5 or 10 mm in diameter at the widest point.