無黄疸で診断された早期胆管癌の1例―超音波診断（US，EUS，術中US）を中心に

Early Bile Duct Carcinoma Diagnosed in an Anicteric Stage: Assessment of Cancer Invasion by Different Ultrasound Modalities, Report of a Case

要旨　無黄疸で診断された65歳，男性の早期胆管癌（深達度fm）症例について，US，EUS，術中USなどの超音波検査所見を中心に報告した．本例は，糖尿病治療中に腹部USスクリーニング検査で無症状，無黄疸で診断され，胆管癌の拾い上げ診断におけるUSの有用性を示唆する症例であった．また，USでは胆管壁に対応する高エコー層が温存されており壁外浸潤はないものと考えられた．EUSでは胆管壁の3層構造が描出され，腫瘤直下で外膜（af）を含む線維筋層（fm）を示す低エコーの第2層が温存されていることから深達度はfm以浅と診断でき，また第1層（粘膜を含む境界エコー）の不整・肥厚の所見から壁内浸潤が診断された．これらの所見は，術中USでも同様であり，切除標本の水浸下USでも確認された．EUS，術中USの所見は病理組織所見によく一致し，胆管癌の深達度・進展度診断におけるEUSおよび術中USの有用性が示された．

　A65-year-old male asymptomatic but with a history of diabetes mellitus underwent, on admission to the hospital, abdominal ultrasonography (US) as a part of the general screening, which revealed a probable bile duct tumor. The patient was forwarded for a close examination with endoscopic ultrasonography (EUS). With EUS, the bile duct was visualized as a three-layer tubular structure: the innermost (1'st) hyperechoic layer corresponding to the border echo including echo from the mucosa, the middle (2'nd) hypoechoic layer corresponding to the fibromuscularis, and the outermost (3'rd) hyperechoic layer corresponding to the subserosa and serosa plus the border echo. The tumor was identified as a papillary hypoechoic mass protruding into the ductal lumen immediately cephalic to the pancreas. The ductal wall from which the tumor had originated presented a derangement (irregular thickening) of the 1'st sonographic layer but the 2'nd and 3'rd layers remained intact. Longitudinal extension of the derangement, i.e., intramural spread, was also detected. However, no other involvement was demonstrated with EUS. Thus, a preoperative diagnosis of early bile duct cancer was established. Laparotomy disclosed a bile duct tumor with neither extramural infiltration nor liver metastasis 〔N (-), S₀, V₀, P₀, H₀, Hinf₀, Panc₀, D, ₀Ginf₀; Stage I〕. The bile duct was resected and the biliary passage was reconstructed with hepaticojejunostomy. Images from intraoperative US and sonograms of the resected specimen immersed in water were perfectly compatible with those from preoperative EUS, thus exemplifying the diagnostic accuracy yielded by preoperative EUS. Histology of the specimen was a papillary adenocarcinoma measuring 15×23 mm with a limited permeation into the fibromuscular layer. The patient has been well without recurrent disease for four years and eight months after surgery.