Diffusion-weighted imaging is a feasible method for screening colorectal cancer: report of a case.

The liver is one of the most common sites for metastatic disease. It is sometimes difficult to detect the primary site. We describe herein the feasibility of diffusion-weighted imaging (DWI) for searching primary site of liver metastases. A 93-year-old male patient presented to us with the chief complaints of hematochezia. Ultrasonography (US) and computed tomography (CT) showed multiple masses in the liver. However, these examinations revealed no primary tumor. DWI showed bright signal mass in the rectum. Furthermore, the apparent diffusion coefficient (ADC) map in that area was depicted as a low ADC value. A histopathological analysis demonstrated the tumor to be moderately differentiated adenocarcinoma. We consider that DWI is a feasible method for screening colorectal cancer, especially for unknown primary site cancers.