CTによる胃癌のstage診断の試み

Computed Tomography for Staging of Gastric Cancer

要旨　胃癌症例88例のCT所見を再検討し，CTによる胃癌のstage診断につき検討した．漿膜面浸潤の程度に関しては全体での正診率77％（68/88）を得た．ただしS₀とS₁とは区別していない．誤診例の中ではS₃の偽陽性例が多かった．腹膜播種性転移の検出率は20％（2/10）であり，肝転移の検出率は83％（5/6）であった．リンパ節転移の程度に関する全体での正診率は59％（47/80）であったが，リンパ節転移陽性例に限ると正診率は37％（17/46）であった．

　Eighty-eight cases of gastric cancers (26 early gastric cancers and 62 advanced cases) were evaluated for staging by computed tomography (CT). Serosal extension of the tumor, intraperitoneal dissemination, liver metastasis, and lymph node metastasis on CT were evaluated according to “The General Rules For The Gastric Cancer Study”, and compared with operative findings.

　Concerning serosal extension of the tumor, the following criteria were used in CT diagnosis. S₂ is defined as protrusion of the serosal surface of the tumor site and/or irregularity of the serosal surface. Smooth and flat serosal surface on CT suggests S₀ or S₁. Differentiation between S₀ and S₁ cannot be made by CT. S₃ is diagnosed by obliteration of fat planes between the tumor and adjacent organs. Comparison between CT and operative findings is shown in Table 1. The overall accuracy of CT diagnosis was 77% (68/88), but for advanced gastric cancer cases, accuracy fell to 68% (42/62). Among misdiagnosed cases, false positive for S₃ was prominent. This will be improved by using decubitus or oblique position scan or thin slice scanning.

　For the diagnosis of intraperitoneal dissemination, CT could detect only 2 of 10 intraperitoneal dissemination cases. Without ascites, intraperitoneal dissemination was difficult to diagnose by CT. Detecting rate for liver metastasis was 83% (5/6).

　Regarding lymph node metastasis, diagnostic ability of CT is limited because CT can detect only the size of lymph nodes. Lymph node metastasis without enlargement cannot be diagnosed by CT and CT cannot differentiate metastatic lymph nodes from inflammatory enlarged nodes. Comparison between CT findings and operative findings for the degree of lymph node metastases is presented in Table 2. The overall accuracy was 59% (47/80), but accuracy fell to 37% (17/46) for cases with positive lymph node metastases. And as for the detectability of each regional lymph node, the detecting rate was even lower. Although diagnostic accuracy is still not satisfactory, CT gives unique information and can be a useful modality for the staging of gastric cancer.