[Imaging modalities in the preoperative staging of rectal carcinoma].

Thorough clinical examination, endorectal ultrasound, and magnetic resonance tomography (MRI) are decisive tools in the pretherapeutic work-up of patients with rectal cancer. Depth of infiltration to the rectal wall as well as involvement of perirectal lymph nodes by the tumor are the key questions to be answered. To receive adequate information from imaging procedures, the right questions need to be asked. The extent of invasion of the rectal wall and exact location of tumor infiltration to neighboring structures can be demonstrated by MRI very well, particularly if imaging planes are acquired at 90 degrees to the position of the rectum. Recent developments in computed tomography (CT) using isotrope voxels allow three-dimensional reconstructions of tumors without loss of imaging quality. Assessment of the primary tumor and its nodal metastases after preoperative radio-(chemo-)therapy is still seriously limited. Fusion of positron emission tomography and CT could be a step towards solving the problem of response assessment in the near future.