肺野末梢の小型肺腺癌に対するMRI拡散強調画像による悪性度の評価 Diffusion Weighted Imaging (DWI) by MRI Evaluates the Subtypes of Peripheral and Small Lung Adenocarcinoma

目的．末梢型の小型肺腺癌を対象として，MRI拡散強調画像の画像解析と切除標本の病理学的な所見とを対比しその有用性を検討した．対象と方法．2005年5月から2007年12月までに当センターで手術を施行した，病理学的な腫瘍長径が2 cm以下の小型肺腺癌38例を対象とした．対象症例を，Noguchi分類のType A+Bを非浸潤癌（n=12），Type Cを初期浸潤癌（n=21），Type D+Eを浸潤癌（n=5）と定義した．病巣部の信号強度（DWI）を脊髄部の信号強度（SC）で割ることでえられた比率（DWI/SC比）を算出した．CTとDWI/SC比の画像解析データをもとにROC（receiver operating characteristic）曲線を作成し比較検討した．結果．各浸潤度別のDWI/SC比（平均値）は非浸潤癌が0.444±0.283，初期浸潤癌が0.985±0.513，浸潤癌が0.790±0.344であった．非浸潤癌と初期浸潤癌（p=0.0021），非浸潤癌と浸潤癌（p=0.0468）との間で有意差を認めた．DWI/SC比は比較的にROC曲線が左肩上がりの傾向を示し，より安定的な結果となった．結論．肺野末梢型の小型肺腺癌に対する高b値拡散強調画像は病変の悪性度（浸潤度）を見極めるのに有用であり，そして近い将来縮小手術の適応など治療方針の決定に関わる付加的な情報を提供するものと思われる．

Objective. We evaluated the usefulness of magnetic resonance imaging (MRI) by comparison of diffusion weighted imaging (DWI) studies and pathological findings in peripheral and small lung adenocarcinomas. Materials and Methods. From May 2005 to December 2007, 38 patients with lung adenocarcinomas measuring 2 cm or less in greatest dimension underwent a surgical operation including preoperative MRI study in Gunma Prefectural Cancer Center. Of all the tumors, 12 were bronchioloalveolar carcinoma (so-called Noguchi type A and B; type A+B group), 21 were adenocarcinomas with mixed subtypes (so-called Noguchi type C; type C group) and 5 were the other histological subtypes of adenocarcinoma (Noguchi type D and E in this study; type D+E group). The signal intensities of a lesion (DWI) and the spinal cord (SC) were severally analyzed in the region of interests (ROIs), and the DWI/SC ratio was calculated with the value of DWI divided by the value of SC. Results. The calculated mean DWI/SC ratio for the lesions were as follows: 0.444±0.283 (mean±standard deviation) for type A+B group, 0.985±0.513 for type C group, and 0.790±0.344 for type D+E group. The mean DWI/SC ratio of type A+B group was significantly lower than those of type C (p=0.0021) and type D+E group (p=0.0468). Conclusion. DWI could therefore be a useful diagnostic modality for differentiating the subtypes of lung adenocarcinomas, and the MRI findings may thus provide useful supplementary information before surgery enabling limited resections.