الفهرس 
Anatomy of the rectumOnly 14 pages are availabe for public view
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Abstract
Colorectal cancer is the third most common cancer worldwide. Around 30-40% of colorectal cancers are located in the rectum. Over the past few years, significant progress has been made in the management of rectal cancer. The advances in preoperative therapies have led to the need of accurate preoperative staging to select those patients who are most likely to benefit from these interventions without subjecting others to unnecessary treatment. Rectal cancers are currently staged using a combination of CT, magnetic resonance imaging (MRI), FDG-PET/CT, and transrectal ultrasonography (TRUS), depending on available facilities and specialist experience.
MR imaging has become the most accurate technique in local staging of rectal cancer, this is due to advances in terms of imaging equipment, coils, and sequences that have progressively improved the technique, with a parallel increase in accuracy. MRI can provide information regarding the site of tumor, the depth of mural and extramural tumor spread, involvement of the circumferential resection margin and indicate the extent of any sphincteral involvement. MRI is superior to CT in detecting spread into surrounding organs, pelvic wall invasion, and subtle bone marrow invasion.
Identification of nodal disease continues to be a problem for radiologists. The problem for morphologic imaging is their dependence on size criterion for diagnosis. There is no significant difference in accuracy rates between CT and MRI. The ability to assess the internal architecture of lymph nodes is a major advantage of MR , the presence of an irregular contour and inhomogeneous signal were found to be the most reliable MRI criteria for lymph node metastasis. USPIO-enhanced MRI is a new promising approach to detect metastatic lymph nodes and are especially of additional benefit in the evaluation of small nodes.
For detection of hepatic metastases; which represent the commonest site for distant metastatic spread, the highest sensitivity is provided with intraoperative US, SPIO or Gd-BOPTA-enhanced MRI and contrast-enhanced CT during arterial portography. MRI can also be used after chemoradiotherapy for locally advanced rectal cancer to evaluate treatment response and to determine the new tumor extent.
The recent introduction of powerful whole-body MRI systems enables imaging of the whole body in a single session through repeated table movements. This technique may be used for rectal cancer staging in the future allowing for local staging and whole-body staging in a single session. Diffusion weighted imaging and perfusion MRI (DCE-MRI) have a growing role in rectal cancer staging .