Background:
Colorectal liver metastasis (CRLM) sometimes diminish or disappear after chemotherapy and difficult to identify during operation.

Material and Methods:
Among consecutive 131 patients undergoing hepatic resection with curative intent, 86 underwent chemotherapy. Of them, 72 patients underwent contrast-enhanced CT, Gd-EOB-DTPA-enhanced MRI, intraoperative ultrasound (IOUS), and CE-IOUS using perflubutane. Disappearing liver metastases (DLM) and tumors 1 cm or less after chemotherapy were assessed.

Result:
A total of 31 DLMs were noted in 10 patients. Four DLMs were visible during IOUS, all of which were also visible during CE-IOUS, and 11 DLMs were visible during CE-IOUS though missed during IOUS. Sixteen DLMs were missed during both IOUS and CE-IOUS; 9 of them were resected using anatomical resection and 7 were not resected. One of the 9 resected DLMs were proven to be CRLM. Three of the 7 followed-up DLMs grew to be apparent CRLM. In summary, 19 of the 31 DLMs were not true complete remission. Fourteen tumors which were visible in preoperative images were 0.5 cm or less in diameter. The sensitivities of contrast- enhanced CT, Gd-EOB-DTPA-enhanced MRI, IOUS, and CE-IOUS for detecting these tumors were 93%, 93%, 86%, 100%, respectively. The sensitivities of those for 40 tumors between 0.6 and 1 cm in diameter were 88%, 93%, 90%, 100%, respectively.

Conclusion:
CE-IOUS would be necessary for the patients with CRLM undergoing preoperative chemotherapy even if Gd-EOB-DTPA-enhanced MRI was performed.