Few localized pneumothoraces can be diagnosed without the aid of the roentgen rays. Indeed, most recent observations on interlobar pneumothorax1 and pleural and pulmonary annular shadows2 are based solely on the routine roentgenologic study of patients suffering from pulmonary diseases.
There are rare cases, however, in which a rapid roentgenologic examination may suggest a localized pneumothorax or hydropneumothorax, when in reality neither condition exists. French writers, who were among the first to recognize this condition, applied the term "faux pneumothorax" to these supposed roentgenologic aberrations. These false pneumothoraces do not cause any definite subjective symptoms, and the physical findings over the area involved are those of thickened pleura with retraction of the lung tissue. There is usually a fluid level in the region of one or the other of the lower lobes of the lung, where these pneumothoraces usually occur. Their appearance either fluoroscopically or on flat or