[Thoracic pathology without apparent radiographic sign: re-interpretation basis].

A chest radiograph may falsely be initially read as being normal or "apparently" normal. The clinical settings where such a false reading may occur are numerous and variable. The most significant situation is the initially missed single pulmonary nodule, with a reported estimated incidence ranging between 30% and 50%. Airway diseases are also typically silent on chest radiographs. The trachea and main bronchi are not well evaluated and some small airways diseases may have very little manifestations, even when advanced. Vascular diseases, when diffuse with bilateral symmetrical hypo- or hyperperfusion, are difficult to detect along with localized but symmetrical vascular disorders and endo- or transthoracic extracardiac shunts. Finally, any disease involving the pleura, pericardium, mediastinum, or lung interstium may be undetectable radiologically at the time of presentation. This paper reviews and illustrates these various diseases and their radiological findings.