Efficacy of two-phase helical CT emphasizing gastric mucosal phase in detection of early gastric cancer with atypical enhancement pattern

To evaluate the efficacy of two-phase dynamic helical CT, including the gastric mucosal phase, for the detection of atypical non-hyperattenuating early gastric carcinoma(EGC). In 32 patients, we evaluated the two-phase helical CT findings of endoscopically suspected EGC for changes of the inner hyperattenuaing mucosal layer, the hypoattenuating outer layer and the serosal surface. Two gastrointestinal radiologists working together reached their conclusions before pathologic diagnosis had been made. The first, so-called gastric mucosal, phase was obtained 38-45 sec after the start of IV injection of 150ml/sec contrast material at a rate of 4ml/sec to obtain maximum enhancement of the mucosal layer. Among 32 patients, EGC was confirmed in 30 and AGC(T2) in two. Using two-phase helical CT, the detection rate for typical hyperattenuaing EGC was 27%(8/30). Lesions showing focal interruption of the mucosal layer without abnormal enhancement of the outer layer(EGC atypical enhancement pattern type 1) were detected in five patients during the mucosal phase, and were pathologically confirmed as 3 EGC IIc + III, 1 IIc + IIa, and I IIb + IIc. Lesions showing a locally protruding lesion of the inner and preserved outer layers, with a smooth serosal surface (EGC atypical enhancement pattern type 2) and which could be distinguished from normal folds, were detected in six patients during the mucosal phase, and were pathologically confirmed as 2 EGC IIb + IIc, 1 IIc + IIa, and 3 IIc + IIb. Lesions were less distinct during the equilibrium phase, and there was no change in the enhancement pattern. The overall detection rate for EGC in which an atypical enhancement pattern was added to the typical one showed improvement (19/30, 63%). Helical CT using two-phasic scan technique including the mucosal phase was efficient for various combinations of EGC II and/or III, including IIc. The findings were atypical and non-hyperattenuaing, but reliable, and improved the overall detection rate