Focal lesions of the liver are a commonly encountered incidental finding. Focal lesions could be benign or malignant, representing a diagnostic dilemma, especially with the high prevalence of viral hepatitis in Egypt. Thus, early diagnosis is warranted to ensure optimal and timely management of hepatic focal lesions. Currently, the guidelines are dependent on ultrasonography and computed tomography; MR is reserved for further characterization since it has higher contrast resolution, safe in vulnerable groups of patients due to radiation-free technique and a safe contrast agent .
Diffusion imaging carries the advantage of using non-contrast agent, in addition to being dependent on tissue cellularity, organization, and integrity of cell membranes. These factors render it useful for detecting malignant lesions and differentiating tumorous from non-tumorous tissues .
In the current study, we aimed to demonstrate the use of diffusion MRI in differentiating benign from malignant liver lesions using the current sequence and comparing it to previously published literature. We used 3 b values 0, 200, and 800 as used in several studies including Demir et al. in 2007, Koike et al. in 2009, and Hosny et al. in 2010 [18,19,20].
In our study, the lesions were detected on DWI. Interestingly, the smallest detected lesion was 0.5 cm, thus demonstrating its capability of detecting small lesions. While cysts and hemangiomas showed facilitated diffusion, solid neoplastic lesions showed restricted diffusion. This came in agreement with Taouli and Koh who reported that cellular hepatic lesions such as tumors demonstrated restricted diffusion at b values higher than 500 s/mm2 . This could be explained by the fact that DWI depends on several factors including tissue cellularity. Since the main target of DWI is extracellular diffusion, high cellular tissue leads to a short diffusion path, resulting in low ADC values as seen in solid malignant lesions. On the other hand, low cellular lesions with less structural barriers as seen in cysts enhance longer diffusion path [21,22,23].
The absolute ADC values of different types of lesions were variable due to differences in techniques applied by b values, different breath measurement techniques, and mathematical logarithms. Petra and Eric stated similar findings in 2010 . The authors compared their findings with previous studies that used different DWI techniques, and reported that some publications preferred using breath-hold, or in other words respiratory triggered DWI, rather than using the conventional T2-weighed MRI, while others favored both modalities in conjunction to obtain better results especially in atypical lesions, in order to avoid artifacts that might occur with measuring techniques of DWI.
The ADC measurement of benign and malignant lesions was significantly different with p value < 0.0001, which comes in agreement with a previous study by Onur et al. 2012. The authors found the mean ADC values differentiating benign and malignant lesions were statistically significant . According to another study, although the authors recommended that the value of DWI should be highly considered, and showed the importance of ADC in focal lesions, they advised it careful interpretation since overlaps may occur between focal lesions as hemangiomas and metastases .
Some studies have indicated that AFP has substantially limited diagnostic accuracy in detecting small HCC . As mentioned previously, AFP may be normal. We hence speculate that combination of AFP and ADC together could be useful in predicting malignancy. Unfortunately, they cannot differentiate primary from secondary malignancy.
Our study has some limitations. First, the DW data set was only respiratory triggered which has some limitations including cardiac motion artifacts and noise contamination that may distort ADC values. Second, the small number of patients included, especially in the subgroups of benign and malignant groups respectively. Additionally, benign lesions were limited to hemangiomas and cysts, while adenomas, focal nodular hyperplasia, and abscesses were not studied. Future multi-center studies with a larger sample size and including more pathologies of benign liver focal lesions are warranted to confirm our findings.