Detectability of peripheral lung cancer on chest radiographs: effect of the size, location and extent of ground-glass opacity

The purpose of this study was to evaluate the effect of the size and location of lung tumour and the extent of ground-glass opacity (GGO) on thin-section CT for the detection of peripheral lung cancer on chest radiographs. 100 posteroanterior chest radiographs of peripheral lung cancer 20 mm in diameter or smaller were reviewed retrospectively by two chest radiologists individually. Lung cancer was detectable on chest radiographs in 51 (51%) cases. However, in six cases, the tumour was recognized not as a nodular opacity but as a subpleural linear or localized hazy opacity. The median size of detectable lung cancer (17 mm) was larger than that of undetectable lung cancer (14 mm; p<0.001). The frequency of tumours with extent of GGO less than 70% was 94% in detectable cases and 59% in undetectable cases (p<0.001). The frequency of tumours located in unobscured lung was 94% in detectable cases and 59% in undetectable cases (p<0.001). The detectability of peripheral lung cancer on chest radiographs is influenced by tumour size, location and extent of GGO seen on thin-section CT. It should also be noted that some tumours may not be recognized as a nodular opacity even if they are detectable.