食道癌リンパ節転移診断の進歩―CT・MRIの立場から：diffusion weighted imageを中心に

Improved Detection of Lymph Node Metastasis in Esophageal Cancer ― Evaluation by Computed Tomography and Magnetic Resonance Imaging : Focus on the Diffusion Weighted Image

要旨　食道癌と診断され，MRIおよびCT施行後に手術が行われた20症例についてDWI，T2WI，CTのリンパ節転移診断能について検討を行い，特にDWIの結果について組織学的所見との対比を行った．DWIの感度，特異度はそれぞれ55.9％，77.4％，T2WIでは23.5％，93.6％，CTでは29.4％，93.1％であった．隔清リンパ節の組織学的検討において，転移陰性群の平均短径は陽性群よりも有意に小さい結果が得られたが，転移陽性群のうち10mm以上のものは2群のみであり，5mm以上10mm未満が26群，5mm未満のものが6群存在した．転移陰性リンパ節は短径5mm未満が125群と最も多く認められたが，一方で10mm以上のものが8群確認された．また転移陽性群のうち4群にmicrometastasisが証明された．リンパ節の肉眼的形状に特異な傾向は認められなかった．DWIの描出能はリンパ節の大きさに依存している可能性があり，非特異的であるが，感度が比較的高く，撮像法の改良とともに今後の有用性が期待される．

　20 patients with esophageal cancer underwent MRI and CT before esophagectomy and lymph node dissection. The detectability of lymph node metastasis by DWI (diffusion weighted image), T2WI and CT were compared, and all images were correlated with the histopathological findings.

　A total of 238 lymph node groups were dissected in 20 patients, of which 34 node groups were malignant on histologic examination. For assessing metastasis in individual groups, DWI showed 55.9％ sensitivity, 77.4％ specificity, whereas T2WI and CT showed 23.5％ and 29.4％ sensitivity, 93.6％ and 93.1％ specificity, respectively.

　In our histological investigation, the mean short axis diameter of non-metastatic lymph nodes were significantly smaller than metastatic lymph nodes. However 6 groups of metastatic lymph nodes were less than 5 mm in short axis diameter and micrometastasis were proved in 4 groups. On the other hand, 8 groups of non-metastatic lymph nodes were greater or equal to 10 mm in short axis diameter in microscopic specimens. In DWI, the depiction of each lymph node group was inclined to be nodal size and not specific for histological feature. The sensitivity of DWI was relatively high, compared with T2WI and CT, and we anticipate that its advantage will lead to improvement in nodal staging.