Chest ImagingInterlobar pleural effusion
collection of
pleural fluid between lobes, i.e. within the major and minor fissures. The
radiographic appearance depends on the shape and orientation of the fissure, the volume of fluid, its position within the fissure and the
radiographic projection. Interlobar fluid is particularly common in heart failure.
Fluid in the minor fissure produces an opacity with a lentiform shape and sharply defined margins on the lateral radiograph. There is an oval or round shape on the frontal view, superficially mimicking a pulmonary mass, hence the term pseudotumour (see pulmonary oedema (V:1), Fig. 1).
Fluid in the major fissure is less common. It is best identified on the lateral projection where it produces a triangular opacity along the line of the fissure, extending inferiorly to the anterior surface of the diaphragm. On the frontal view, there is hazy opacification of the lower hemithorax, more transradiant medially.
On CT interlobar pleural fluid appears as a well-defined opacity of fluid attenuation between the fissures.
CF - HM