Liver cancer is the tenth most common cancer among men and is eighth among women.1 It is estimated that 42,220 adults will be diagnosed with liver cancer this year. Despite what these statistics appear to mean, men are more likely to develop primary liver cancer. The overall five year survival rate is 18%, with slightly improved chances if the disease is caught in an early stage. There are three main types of liver cancer: hepatocellular carcinoma (HCC,) cholangiocarcinoma (bile duct cancer) and angiosarcoma.2 Each type of liver cancer affects different aspects of the liver. HCC is cancer in the main portion of the liver and affects 80% of people with liver cancer. Bile duct cancer comes from cells in the bile duct, or thin tubing from the liver to the small intestine, and affect 10-20% of liver cancer patients. Angiosarcoma is cancer in blood vessels and spreads quickly. Angiosarcoma affects about 1% of liver cancer patients. Imaging tests, including magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound (US) are conducted to diagnose, stage, and monitor liver cancer.3
US is most commonly used in screening exams since it is easily available and inexpensive. However, studies have shown that US has a lower sensitivity than MRI. A retrospective study was conducted on 35 patients with surgically removed or biopsy-proven tumors to compare US, CT, and MRI.4 Multiple types of MR imaging were examined, including gadolinium-enhanced, STIR, and conventional. MRI was shown to have an advantage over US in 16 of these cases, while US had an advantage for only two cases. US and MRI were equally accurate in 17 other cases. This shows how MRI can be more effective for screening for cancer. Likewise, researchers conducted a prospective study of 407 patients in which both MRI and US were used to screen for liver cancer.5 The study found that of the 43 patients with HCC, MRI with gadoxetic acid enhancement identified 37 total cases, meaning MRI had a detection rate of 86%. US only detected a total of 12 cases, with 11 of those cases overlapping between the two methods, giving US a detection rate of 27.9%. US only picked up one case that MRI did not, though five cases were detected on neither method. Doctor's should consider replacing US with MRI for screening of high-risk patients due to ultrasound's inferior detection rate.
CT and MRI are both commonly used in diagnosing and staging liver cancer, though some prefer CT to MRI due to cost effectiveness. However, the study of 35 patients mentioned above also compared CT and MRI and found MRI to be more advantageous.4 MRI was more informative in 10 cases and equally informative in 21 of the cases. CT was more informative in four cases. Although it is a much smaller margin than with US, MRI proved substantially more sensitive than CT. James P. Earls conducted a review of comparison studies of MRI and CT that was published on June 1st, 2000.6 Although he emphasizes that MRI is more expensive, Earls identifies MRI as the superior imaging method in a variety of areas. He states that MRI has greater accuracy at detecting hepatic lesions, has greater specificity, and greater accuracy in detecting focal hepatic neoplasms. MRI should be used when possible to diagnose and monitor liver cancer due to its higher accuracy, sensitivity and specificity compared to CT.
What MR imaging tells physicians
Early HCC diagnosis is hindered by the sensitivity of imaging tests in relation to the size of a nodule. Nodules first are noted on US, since this is the typical screening method for HCC. Once they have been noted, nodules are usually biopsied, because this is the only way to be sure that the results are sound. However, biopsies are not one hundred percent accurate either and can be affected by sampling error.7 Therefore, it is important to resolve this issue, preferably with a non-invasive technique. In a comparison study, contrast-enhanced US (CEUS) and dynamic MRI were used to monitor 89 nodules that were smaller than 20 mm in size. Of these nodules, 13 were less than 10 mm, and only two of these were HCC, meaning that the likelihood of smaller nodules being HCC is low. The larger nodules are easier to diagnose due to obvious variations in the test. MRI had an extremely high accuracy rate (96.77%) on its own. In cases larger than 15 mm, MRI was 100% accurate. Based on this evidence, MRI could easily be used as a more accurate method of confirming malignancy in small nodules and help with the early diagnoses of HCC.
MRI not only helps to diagnose and monitor tumors but also to monitor radiotherapy. To do this, radiologists use diffusion-weighted MR imaging (DWI.)8 DWI is a form of MRI used to monitor the changes in molecular motion during MR sequences. The changes are measured as apparent diffusion coefficients (ADC) and can help measure tumor control and tissue injury. Studies have found that DWI has been able to identify whether a tumor will respond to a treatment based on how the tumor's mean ADC changed. If the ADC increases, the treatment is likely to work well. These changes are most evident in the first week of treatment and predate the first obvious representation of treatment response. DWI could be used to determine how well a tumor will respond sooner than regular imaging and could prevent a patient staying on a treatment that will not be beneficial.
MRI has proven useful in every stage of cancer diagnosis and treatment. Although ultrasound is currently the preferred method to screen for liver cancer, MRI is more sensitive to developing cancers and could help with early diagnosis and increased survival five-year survival rate for patients. Once cancer shows up on a screening exam, CT and MRI are both used. However, MRI again shows a higher sensitivity rate than CT. Not only does MRI show more than CT, but it also can be used to determine malignancy, even at a size of 20 mm and smaller. Finally, DWI can be used to determine how a patient will respond to therapy once treatment has begun. Through each of these uses, MRI could be used for early detection and thus increase the five-year survival rate. This could help not only the 42,220 newly diagnosed men and women but also those previously diagnosed with liver cancer.
1. Cancer.Net Editorial Board. "Liver Cancer: Statistics." Cancer.Net. January 2018. Web. 31 October 2018. <https://www.cancer.net/cancer-types/liver-cancer/statistics>.
2. Cancer.Net Editorial Board. "Liver Cancer: Introduction." Cancer.Net. May 2015. Web. 31 October 2018. <https://www.cancer.net/cancer-types/liver-cancer/introduction>.
3. The American Cancer Society medical and editorial content team. "Tests for Liver Cancer." cancer.org. 31 March 2016. Web. 31 October 2018. <https://www.cancer.org/cancer/liver-cancer/detection-diagnosis-staging/how-diagnosed.html>.
4. Walter L. Curati, et al. "Ultrasound, CT, and MRI comparison in primary and secondary tumors of the liver." Gastrointestinal Radiology. December 1988; 13(1): 123-128. Web. 6 November 2018. <https://link.springer.com/article/10.1007/BF01889040>.
5. Dave Pearson. "MRI bests ultrasound for cancer screening of cirrhotic livers, but is it fiscally feasible?" Oncology Imaging. 22 September 2016. Web. 6 November 2018. <https://www.healthimaging.com/image-category/oncology-imaging/mri-bests-ultrasound-cancer-screening-cirrhotic-livers-it-fiscally>.
6. James P. Earls. "Comparison Studies of CT and MRI in Patients With Hepatic Metastases." Oncology. 1 June 2000; 14(6). Web. 31 October 2018. <http://www.cancernetwork.com/review-article/comparison-studies-ct-and-mri-patients-hepatic-metastases/>.
7. Alejandro Forner, et al. "Diagnosis of hepatic nodules 20 mm or smaller in cirrhosis: Prospective validation of the noninvasive diagnostic criteria for hepatocellular carcinoma." Hepatology. 26 December 2007; 47(1): 97-104. Web. 5 November 2018. <https://aasldpubs.onlinelibrary.wiley.com/doi/full/10.1002/hep.21966>.
8. Cynthia L. Eccles, et al. "Change in diffusion weighted MRI during liver cancer radiotherapy: Preliminary observations." Acta Oncologica. 8 October 2009; 48(7): 1034-1043. Web. 31 October 2018. <https://www.tandfonline.com/doi/full/10.1080/02841860903099972?scroll=top&needAccess=true>.