“…In many publications, PP and DPT are not distinguished or diagnostic criteria are not described [Ohlson et al, 1985;Oliver et al, 1985Oliver et al, , 1988Hilt, 1987;Anton-Culver et al, 1989;Delclos et al, 1990;Balmes et al, 1991;Levin and Selikoff, 1991;Selikoff et al, 1991;Anderson et al, 1992;Ehrlich et al, 1992;Oksa et al, 1992;Welch et al, 1994]. Some authors quote the ILO classification, without any other details [Cotes and King, 1988;Hessel et al, 1988;Demers et al, 1990;Kilburn and Warshaw, 1990;Kouris et al, 1991;Bresnitz et al, 1993;Fischbein et al, 1993;Rey et al, 1993]. In order to facilitate the reading of pleural abnormalities and to reduce inter-and intra-reader variability, obliteration of costophrenic angle has been proposed to characterize DPT on postero-anterior chest-X-rays [Sargent et al, 1978;Bourbeau and Ernst, 1988;Bourbeau et al, 1990, Kennedy et al, 1991Lilis et al, 1991Lilis et al, , 1992Miller et al, 1992;Schwartz et al, 1994;Garcia-Closas and Christiani, 1995].…”