PLEURAL CYSTS are rare developmental anomalies which involve the parietal pleura, most commonly on the diaphragmatic surface. These cysts contain serous fluid of low specific gravity and are composed of a thin fibrous wall with an inner mesothelial layer. They are analagous to the "spring-water" cysts (pericardial coelomic, pleuropericardial cysts) which arise from the parietal pericardium.
A pleural cyst is radio-opaque and if sufficiently large and appropriately situated, may be visible on the chest roentgenogram. Depending upon its location, it may simulate a chest-wall tumor, a diaphragmatic tumor, a mediastinal tumor, or a subpleural intrapulmonary solitary circumscribed mass.
In 1936, Freedman and Simon1 reported a case of a simple cyst of the parietal pleura situated on the left diaphragm, and reviewed 16 cases of pleural cysts in the German literature. Only a few scattered reports have appeared subsequently. Because of the rarity of these lesions, it is of interest
Jamplis RW, Lillington GA, Mills W. Pleural Cysts Simulating Mediastinal Tumors. JAMA. 1963;185(9):727-728. doi:10.1001/jama.1963.03060090059023