Background/aims: Diffusion-weighted imaging (DWI) is a new magnetic resonance (MR) imaging technique that evaluates the diffusion of water molecules. Its clinical usefulness in the acute stage of cerebral infraction has been established. Recent technical developments have enabled DWI for human body and the usefulness of DWI for detecting malignant tumors such as liver, kidney, ovary, and breast tumors has been reported. This study documents cases of colorectal cancer detected by DWI and discusses the efficacy of DWI for the evaluation of colorectal cancer.

Methodology: DWI, computed tomography (CT) and colonoscopy examinations were performed on 18 patients with colorectal cancer. MRI examinations were performed using a 1.5-T imager (Toshiba, Otawara, Japan). The signal intensity was measured in a series of DWI and the apparent diffusion coefficient (ADC) values were calculated in order to differentiate the cancers from normal tissues. Two experienced radiologists evaluated the depth of tumor invasion into the colorectal wall (tumor staging), the involvement of regional lymph nodes (nodal staging), and the presence or absence of metastasis (metastatic staging) on DWI and CT images according to the TNM classification system. TNM staging of each tumor was compared with the pathologic and surgical findings.

Results: There were no differences between the DWI and the CT images regarding their abilities to detect early colorectal cancer. However, DWI could detect advanced colorectal cancer and liver metastasis more sensitivity, or accurately than CT with no enhancing material. In one patient who did not undergo a surgical resection, a follow up DWI showed peritoneal seeding and bone metastasis.

Conclusion: Although DWI has a difficulty to detect early colorectal cancer, DWI has the potential to be clinically effective for the evaluation of preoperative TNM staging and the postoperative follow-up of colorectal cancer.