Which other simple investigation can confirm a subpulmonic effusion seen on frontal x-ray ?
A simple Xray chest decubitus view will show the fluid gravitating into the lateral pleural margin, confirming the diagnosis.
There is another subtle sign to diagnose subpulmonic effusion here, can you see it ?
The lung markings stop abruptly at the left diaphragmatic outline, due to the dense fluid opacity, the normal translucency of the diaphragm is lost.
The left dome of diaphragm is higher than right with increased distance of diaphramatic outline to the fundal air bubble of stomach, suggestive of a subpulmonic pleural effusion.