In many patients, neoadjuvant chemotherapy for colorectal liver metastasis shrinks metastatic tumors and simultaneously makes liver metastases undetectable on CT images (disappearing liver metastases [DLM]). This phenomenon occurs in 5–38% of patients with colorectal liver metastasis who receive neoadjuvant chemotherapy. Diagnostic imaging results may be often affected by image quality, there is only a 20–100% rate of agreement between cases of pathological (pCR) and radiologic complete response (rCR), showing that pCR and rCR are not equivalent.
Tani et al. compared EOB-MRI (Gd-EOB-DTPA enhanced MRI) and contrast-enhanced intraoperative ultrasound (CE-IOUS) for their ability to detect DLM after neoadjuvant chemotherapy for colorectal liver metastasis1). The results showed EOB-MRI diagnosed DLM with an accuracy of 0.88 compared to 0.68 for CE-IOUS. Tani et al. also evaluated clinical outcomes (residual lesion after DLM resection [yes/no], re-growth of non-resected DLM during follow-up [yes/no], etc.) when DLM were detected or not detected by EOB-MRI and CE-IOUS. EOB-MRI diagnosed residual DLM and DLM tumor re-growth with a positive likelihood ratio/negative likelihood ratio of 6.84/0.12 and CE-IOUS diagnosed the same with a positive likelihood ratio/negative likelihood ratio of 2.03/0.45, suggesting better detection performance by EOB-MRI. The DLM treatment algorithm created by Tani et al. based on these findings is shown in Fig. 1.
(1) Colorectal liver metastasis
Sofue et al. (2004) compared the diagnostic performance of contrast-enhanced CT and combined contrast-enhanced CT plus EOB-MRI in detecting colorectal liver metastasis and evaluated how initial treatment plans change when EOB-MRI is combined with contrast-enhanced CT13). The study was conducted in 39 patients with histologically veried liver metastasis (85 lesions). Colorectal liver metastases were detected with significantly higher sensitivity (91.0% vs. 79.2%) and a significantly higher Az value (0.929 vs. 0.853) in the group examined using both contrast-enhanced CT and EOB-MRI than in the group examined using only contrast-enhanced CT.
The surgical plan was also altered in 13 of 39 patients (Fig. 21).
(2) Pancreatic liver metastasis
Ito et al. (2017) studied 201 patients with pancreatic cancer diagnosed as resectable based on contrast-enhanced CT and ultrasonography who then underwent EOB-MRI before surgery. The utility of EOB-MRI in diagnosing liver metastasis was investigated in these patients18). Thirty-seven lesions in 17 patients were diagnosed as potential liver metastases based on EOB-MRI of which the final diagnosis was a liver metastasis for 31 lesions (12 patients) and a benign tumor for 6 lesions (5 patients; 3 hemangiomas and 3 abscesses). Pancreatic liver metastases were detected by EOB-MRI with 77.5% sensitivity, 94.7% specificity, 90.2% accuracy, 83.8% positive predictive value, and 92.3% negative predictive value.
Pancreatic cancer is often deemed incurable by resection based on the presence of liver metastasis or other distant metastases at diagnosis. Although finding distant metastases rules out surgery as an option, very small liver metastases can sometimes be missed by high-resolution CT, which is the current gold standard imaging method. Accordingly, more precise methods of detecting liver metastasis before surgery should be considered to avoid unnecessary surgery.