[Current MRI staging of rectal cancer]

Colorectal carcinoma is the second most prevalent cause for cancer, and has very variable outcomes. Advancements in surgery, the change from adjuvant to neo-adjuvant radio-chemo-therapies as well as in clinical diagnostics have improved the prognosis for patients in a multi-modal therapy concept. An accurate primary staging including a reliable prediction of the circumferential resection margin (CRM) has established MR Imaging (MRI) beside intraluminal endoscopic ultrasound (EUS). MRI facilitates the selection of patients likely to benefit from a preoperative therapy, especially in cases of unfavorable factors. Currently the relationship of the tumor to the mesorectal fascia has become a more important prognostic factor than the T-staging, particularly for surgical therapy. In addition further prognostic factors like the depth of infiltration into the perirectal fat and the extramural venous infiltration (EMVI) have important impact on therapy and prognosis. High resolution MRI has proved useful in clarifying the relationship between the tumor and the mesorectal fascia, which represents the CRM at the total mesorectal excision (TME) especially in the upper and middle third. Preoperative evaluation of the other prognostic factors as well as the nodal status is still difficult. It is used increasingly not only for primary staging but also progressively for the monitoring of neoadjuvant therapy. The addition of diffusion weighted imaging (DWI) is an interesting option for the improvement of response evaluation. The following overview provides an introduction of MRI diagnosis as well as its importance for the evaluation of the clinically relevant prognostic factors leading to an improvement of therapy and prognosis of patients with rectal carcinoma.