The classic and most obvious presentation of a small pleural effusion on a radiograph is blunting of the lateral or posterior costophrenic sulcus, a form of parietal-visceral pleural separation.
Additional signs include the "deep sulcus" sign, a deepening and widening of the costophrenic sulcus due to intrapleural gas tracking inferolaterally, (11) and the "double diaphragm" sign (Figure 9), the presence of two diaphragm-gas interfaces, classically at the dome and anterior costophrenic sulcus.
Free-flowing fluid first accumulates in the posterior costophrenic sulcus
, a location frequently occult in semi-recumbent patients.
(24) Radiographic findings include hyperlucency in the lower chest, depression of the ipsilateral diaphragm and deepening of the lateral costophrenic sulcus
. (23) Non-dependent crescentic lucency in the pleural space is seen on CT (deep sulcus sign).
A chest radiograph (Figure 1) showed pleural thickening in the region of the costophrenic sulcus
, enlargement of the hilar and paratracheal lymph nodes, and a mass in the right upper lobe.