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CT and PET
Advances in imaging technology have greatly improved the ability of CT to stage gastric tumors. While not as extensively studied as EUS, multidetector row CT (MDCT), by which the wall of the stomach can be seen as 3 layers (an inner layer corresponding to the mucosa, an intermediate layer corresponding to the submucosa, and an outer layer of slightly higher attenuation corresponding to the muscularis propria and serosa), appears to have comparable accuracy to EUS in terms of both T and N staging. The loss of fat planes between the gastric mass and an adjacent organ suggests tumor invasion. The accuracy of MDCT for overall T staging ranges from 77% to 91%, and discriminates serosal involvement with an accuracy of 83% to 100%.340,341 Accuracy with respect to N staging may be as high as 89% with MDCT.342,343 As with all other imaging modalities, CT has difficulty discerning metastases in lymph nodes smaller than 5 mm. At present, the role of CT is mainly for the detection of distant metastases and as a complement to EUS for assessing regional lymph node involvement. It is not yet clear whether EUS or MDCT (or the combination) is superior for T and N staging in gastric cancer, and the underlying technology continues to evolve and improve.
PET scanning alone is not recommended as a sole imaging test for gastric cancer staging, largely because most gastric adenocarcinomas have low FDG uptake and there are false positives as well (see Chapter 52).344 However, in patients initially staged as having localized gastric cancer, combined PET/CT increases the detection of metastatic disease by 10%, thus altering clinical management.345