[Comparison between endorectal MRI (EMRTI) and endorectal sonography (ES) after surgery or therapy for rectal tumors to exclude recurrent or residual tumor]

Preoperative staging of colorectal cancer--computed tomography and magnetic resonance imaging

Cross-sectional imaging techniques are increasingly being used in the preoperative evaluation of patients with colorectal cancer. Both computed tomography (CT) and magnetic resonance (MR) imaging have been improved with significant advances of the technological hard- and software. This has contributed to high patient acceptance due to shorter examination times and more open configuration of the systems, consistent high quality images with better delineation of the normal abdomino-pelvic anatomy and pathology. New techniques such as CT-colonography have emerged from a research application to a clinical tool which can be used in different clinical settings. Phased-array receiver coils have significantly increased the usefulness of MR in the evaluation of rectal neoplasms due to the high resolution that can be obtained. New organ specific contrast agents for magnetic resonance imaging have facilitated the preoperative evaluation of liver metastases in favour of more invasive techniques with similar sensitivities. However, preoperative staging criteria for colorectal cancer using computed tomography and magnetic resonance imaging has to be updated and the results of new techniques have to be confirmed in large trials. In the future, further development of CT and MR may offer 'one-stop-shopping' protocols for both diagnosis, local and distant staging of colorectal cancer. Diffusion weighted MR-imaging, in vivo spectroscopy as well as further targeted imaging, such as with lymph node specific agents for MR may also prove to be helpful in the preoperative evaluation of patients with colorectal cancer.

Magnetic resonance imaging predicts sphincter invasion of low rectal cancer and influences selection of operation

BACKGROUND

With the development of numerous sphincter-saving surgical techniques in the last 2 decades, the indication for abdominoperineal resection in radical-elective operations has been markedly reduced. The preoperative assessment of the extent of local tumor growth is essential for the planning of the optimal surgical procedure. Magnetic resonance imaging (MRI) proved to be a reliable method for local staging of low rectal carcinoma. The objective of this study was to determine the frequency of sphincter invasion in an unselected population with low rectal cancer.

METHODS

From 1997 to 1999, 40 patients with histologically verified adenocarcinoma of the lower rectum (+/-5 cm above the linea dentata) without evidence of metastases underwent a MRI with a body coil (no anal endocoil). The MRI results were compared with the operative situs and with pathohistologic findings.

RESULTS

An infiltration of the sphincter ani internus was observed in 11 cases (28%), and a combined infiltration of the sphincter ani internus and externus was found in 2 patients (5%). The median distance of the lower tumor edge to the upper border of the anal canal was 2.0 cm (range, 0-4.5 cm). No infiltration of the external sphincter was observed in patients with cancers above the anal canal. Nine patients (22%) were treated with intersphincteric resection and coloanal anastomosis, 12 (30%) with ultralow resection, and 11 (28%) with low anterior resection of the rectum in conjunction with coloanal anastomosis or a stapled anastomosis. Eight (17%) of the patients were treated with abdominoperineal resection.

CONCLUSION

An infiltration of the internal sphincter occurs only in 28% of low rectal cancers; an infiltration of the external anal sphincter is extremely rare and occurred only in patients with cancers located in the anal canal. Pelvic MRI offers a precise preoperative visualization of sphincter infiltration in patients with low rectal cancers and is therefore a valuable tool for planning of rectal surgery.