In the usual situation, there is a similar retractile force applied to the entire pleural space by adjacent lung. When there is a pleural effusion, the elastic recoil of the lung causes each lobe to retract toward the hilum. This in turn can widen the fissure and can draw fluid into the fissure even in non-dependent locations.
The middle lobe (being the smallest lobe), has the greatest tendency to retract, and therefore the horizontal fissure is more to develop a pseudotumour.
Pseudotumors almost always occur with transudates: caused by congestive heart failure, cirrhosis, or renal insufficiency.
Diagnostic in most cases and can show a lenticular or biconvex opacity along an expected course of a fissure. The concurrent presence of a dependent pleural effusion aids in recognising of a pleural pseudotumour.
May be useful in difficult cases in which the fluid is situated along the edge of the lung, is difficult to relate to a fissure, or has an unusual shape, leading to misinterpretation as a pleural mass.
Treatment and prognosis
They usually resolve after therapy with diuretic agents or treatment of the underlying predisposing condition.