Imaging evaluation
Case 201
【Progress】
She was scheduled to receive tumor resection for hepatic metastases at S6. However, enhanced CT and diffusion WIMRI showed total three metastases; one at S6 and two at S4. Accordingly, the treatment option was altered from surgical resection to chemotherapy.
【Discussion】
Although hyper-vascular liver metastases arise from gastro-intestinal stromal tumor (GIST), melanoma or others, most metastatic liver tumors would rather be categorized into hypo-vascular metastases. Non-enhanced CT and/or Contrast-enhanced CT is often routinely conducted to investigate liver metastases, especially after surgical resection of digestive organ cancer. The relatively large nodule more than 10 mm can be found in irrespective of non-enhanced CT or enhanced CT (Figs 1, 2). However, minute liver metastasis sized less than 5 mm, can be overlooked by interpreters. It is important to recognize which phase image on CT is most sensitive to show the minute liver metastases. From our results of Figs 3 and 4, minute metastasis of 3 mm and 5mm were demonstrated only on the portal phase of contrast-enhanced CT.
Thereafter, EOB-enhanced MRI was conducted to investigate liver metastases. There are many sequences for imaging liver metastases: T1WI (out of phase, in phase), T2WI, fat suppression T2WI, heavy T2WI, Diffusion WI, ADC values, Arterial phase, Portal phase, Delayed phase, and Hepatocyte phase. In the situation of relatively large nodule sized 10 mm or more, the nodule can be demonstrated on MRI with each sequence (Fig. 10). However, in the situation of the minute nodule less than 5 mm, the nodule cannot always be visualized. It is important to recognize which image on MRI is most sensitive to show the minute liver metastases. From our results of Figures 5-10, Diffusion WI is the most sensitive sequence to find the minute nodules as high signal intensity (Fig. 5). It is true that hepatocyte phase MRI also clearly demonstrates minute metastases but its signal intensity is low signal intensity, indicating the need to differentiate from portal branches or small cysts (Fig. 6). Other sequences MRI might demonstrate the minute metastases, but it is also difficult to differentiate from portal branches or small cysts (Figs 7-9). ADC values do not always become lowering because voxel size is coarse and the nodule is very small (Fig. 5). Then, of the many sequences MRI, Diffusion MRI is the most sensitive and reliable to find the minute liver metastasis sized less than 5mm, followed by hepatocyte phase MRI to assure the existence of the minute nodule.
In one literature, sensitivity for liver metastases from colon-rectal cancer is better on MRI than on CT: 91% vs 82% (1, 2). In another literature, EOB MRI is increased diagnostic confidence to 98.3%: contrast-enhanced CT 65.2% and Gd-enhanced MRI 85.7% (1, 3). This difference implies that the minute nodules are more demonstrated on EOB MRI than Gd enhanced MRI and contrast-enhanced CT.
The treatment option for liver metastases from colon-rectal should be decided by multidisciplinary discussion in each case (4-7). In our hospital, resection and chemotherapy are directed by gastrointestinal surgeon. She had previously resection for lung metastasis from sigmoid colon cancer. This time, three hepatic nodules were newly found: one of them existed at S4 area, adjacent to between right hepatic vein and middle hepatic vein, indicating deep site of the liver which is hard to resection. Then, treatment option was altered from surgical hepatic resection to chemotherapy.
【Summary】
We present a seventy seven-year-old female with two minute metastatic liver tumors sized 3 mm and 5mm at S4, and a relatively large nodule sized 28 mm at S6. Contrast-enhanced CT and EOB-enhanced MRI showed the existence of the minute nodules as well as the relatively large nodule. It is borne in mind that a portal phase on contrast-enhanced CT is more sensitive than any other phase to detect the minute liver metastases. Diffusion WI MRI is the most sensitive sequence of all the sequences of EOB enhanced MRI, followed by hepatocyte cell MRI.
【References】
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2020.8.19