Limitations of intraductal ultrasonography in differentiating between bile duct cancer in stage T1 and stage T2: In-vitro and in-vivo studies

Background and Study Aims: We investigated whether intraductal ultrasonography (IDUS) could distinguish between stage T1 and T2 bile duct cancer. Materials and Methods: In-vitro study. Resected bile duct specimens (n = 8) were immersed in a water tank and were pierced with straight pins to clarify the normal layer structure. Ultrasonosgraphic images (20MHz) of the positions of pin echoes were compared to the positions of pin holes as seen on histologic analysis of the specimens. In-vivo study. A thin-caliber high-frequency (6Fr, 20MHz) ultrasonic probe was inserted into the bile duct via a transhepatic route or a transpapillary route in 26 patients with bile duct cancer who underwent surgical resection. Results: In-vitro study. The inner hypoechoic layer on the IDUS image corresponded not only to the fibromuscular layer but also to a part of fibrous layer of the perimuscular loose connective tissue on histologic analysis, especially in the cases with moderate to severe bile duct wall fibrosis. The outer hyperechoic layer corresponded to the subserosal fat tissue. In-vivo study. In four of six patients with tumor limited to the inside hypoechoic layer on IDUS images, the histologic findings showed tumor invasion to the fibrous layer of the perimuscular loose connective tissue. Due to this limitation, accuracy of IDUS in T-staging was only 20/26 (77%). Conclusions: IDUS cannot reliably distinguish bile duct cancer in stage T1 from that in stage Ti.