In the current study, the majority of incidental findings on WB-MRI/DWIBS were considered as clinically non-significant. However, some incidental findings were clinically significant with higher prevalence in older patients, and these may have impacts leading to changes in treatment strategy. It should be emphasized that 19 of the 27 significant incidental findings (70.4%) in 26 patients were found on axial T2WI. We reconfirmed that T2WI plays an important role when reviewing DWI, as a previous study mentioned . Instead of focusing only on DWIBS, T2WI must also be carefully evaluated.
Some previous studies have evaluated incidental findings on WB-MRI [13–15, 18–20]. The prevalence of significant incidental findings in our study (21.0%) was similar to that in previous studies (2.9–36.8%). Of those six previous studies, only three applied DWI/DWIBS in the study protocols, and none of them mentioned the sequences from which incidental findings were identified. In a previous study of WB-MRI with DWIBS in patients with prostate cancer, incidental findings were found in only 31% (31/100) of them . This lower detection rate was probably due to the research focus, comparing DWIBS with bone scintigraphy and CT for the detection of bone metastasis. Actively searching for extraosseous lesions likely increase the detection rate of incidental findings.
In our study, only 1.6% of patients (2/124) showed lung nodule or pulmonary hilar mass, although these findings were reported to be found in 3.8% (4/104) and 4.4% (15/344) of patients on whole-body CT [22, 23]. This is probably due to the limited role of MRI in the detection of lung nodules, given the lower spatial resolution compared to multidetector-row CT and the physiologic noise associated with cardiac and respiratory motions.
The issues regarding incidental findings are not only how often they occur, but also how much impact they have clinically and how to report them. Radiologists should play critical roles in deciding whether a detected lesion is benign or having potential clinical importance. In this study, we categorized the incidental findings into two groups based on the necessity of further work-up—trying to classify the findings according to the most common situations in daily practice. In our study, six patients (4.8%) were considered as having lesions highly suggestive of second malignancy. This result was quite important, since these findings potentially lead to changes in treatment strategy of patients with prostate cancer. Furthermore, additional examinations such as CE-CT were required for further investigation of these findings, they can lead to increased healthcare costs and radiation exposure. Although WB-MRI/DWIBS can provide a comprehensive evaluation of whole-body in cancer patients—detecting metastasis not only in bone marrow, but also in lymph node or other organs—it is not an almighty technique, and additional work-up for evaluation of encountered incidental findings is inevitable. These kinds of suspected malignant lesions were also found in patients with other diseases such as lymphoma (4.4%), neurofiblomatosis (1.6%), and multiple myeloma (2.9%) in previous studies with WB-MRI [18–20]. Clinicians should inform patients of these possible incidental findings and the additional examination prior to WB-MRI/DWIBS as part of their informed consent process.
This study had several limitations. First, incidental findings in our study were diagnosed based on MRI features, in the absence of clinical or pathological confirmation. Second, we did not have access to clinical follow-up data for most patients, as all of our patients received primary care in other clinics or hospitals and visited the study site only for imaging consultations.