ラジアル型細径超音波プローブによる胆外胆管癌の進展度診断

Evaluation of Intra Bile Ductal Ultrasonography for the Diagnosis of Tumor Invasion in Cases of Bile Duct Cancer

要旨　ラジアル型細径超音波プローブを用いた胆管内超音波法（IBUS）の肝外胆管癌進展度診断における有用性につき検討した．基礎的検討では，胆管壁内側高エコー層は粘膜層を含む境界エコー，中間低エコー層は主に線維筋層と外膜層，外側高エコー層は漿膜下層に対応し，腫瘍は低エコー層の肥厚として観察された．腫瘍エコーと血管の接触状態を基準として大血管浸潤の有無が診断可能（正診率100％）であり，腫瘍エコーの外縁形状を基準に，外膜層を越えるか否かの壁深達度・膵浸潤診断が可能（正診率91.7％）であった．壁内進展診断は低周波数プローブでは困難な例が多く，今後の課題と思われた．現時点で本法は胆管横断面方向の進展度診断に有用と考えられた．

　Intra bile ductal ultrasonography (IBUS) is a new method to get ultrasonic images by scanning from the lumen of the bile duct with a miniature size ultrasonic probe. We made an evaluation of IBUS for the diagnosis of tumor invasion in cases of bile duct cancer.

　The ultrasonic image of the bile duct wall consisted of three layers; high-low-high echo areas, and bile duct cancer was shown as the thickness of the second low echoic layer. It was considered from comparison with the pathological section that the inner high echoic layer corresponds to the marginal echo and the mucosal layer (m), the low echoic layer corresponds to the fibromuscular layer (fm)～ adventitia fascia (af), the outer high echoic layer corresponds to the subserosal layer (ss).

　Clinically, based on these results, the depth of the tumor invasion (≦af or ss＜) and the pancreas invasion by the tumor was accurately evaluated in 91.7% of the operated cases of bile duct cancer from the shape of the outline of the tumor echo. IBUS also provided accurate diagnosis of the invasion to the large vessels in all of the operated cases from the state of contact between the tumor and the large vessels. But it is difficult to detect submucosal infiltration of the cancer by IBUS with a low frequency probe. In conclusion IBUS with a radial miniature probe is useful for the evaluation of the depth of the tumor and the invasion to the large vessels.