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Rectal cancer can be accurately staged using preoperative magnetic resonance imaging if the technique and sequence parameters are optimized, and the reader is familiar with the anatomy, limitations of the technique, and features of the disease.
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Many centers currently perform only noncontrast imaging owing to the fact that gadolinium does not significantly aid in the T staging or differentiation of benign from malignant lymph nodes.
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The circumferential resection margin, as well as presence of
Magnetic Resonance Imaging of Rectal Cancer
Section snippets
Key points
Anorectal anatomy
The rectum extends cranially over a distance of approximately 16 cm from the anocutaneous line (anal verge) and is divided into upper (12–16 cm), middle (6–12 cm), and lower thirds (<6 cm).4 The lower two-thirds form the rectal ampulla. The rectum is divided into thirds by the valves of Houston, which are transverse folds 12 mm in thickness composed of the circular layer of the rectal wall. Their function is to support the weight of fecal matter and prevent the urge to defecate. The rectum
Patient Preparation
Before the MRI examination, the patient is asked to prepare the rectum by a sodium biphosphonate and sodium-phosphate enema. Thereafter, a 16 F Foley catheter is inserted into the rectum, and 60 cc of a mixture of a 8:1 dilution of barium sulfate suspension 15% weight per volume (200 cc) and ferumoxsil (25 cc) (are injected. If the study is being completed on a 3T magnet, then the recommended dilution is 16:1. The Foley catheter is left in place for the remainder of the examination. The rectal
T Stage
T (tumor) stage stands for depth of rectal wall invasion by tumor. In general, rectal tumors are minimally hyperintense on T2-weighted imaging relative to the adjacent bowel wall. This is why a positive contrast agent can help when distending the rectum, as it allows for better delineation of the mass. The rectal tumor can present as a polypoid, flat or carpet-like, semicircumferential, or fully circumferential lesion. Rectal cancers typically demonstrate avid enhancement after contrast
Summary
Rectal cancer can be accurately staged using preoperative MRI if the technique and sequence parameters are optimized and the reader is familiar with the anatomy, limitations of the technique, and features of the disease. Many centers currently only perform noncontrast imaging owing to the fact that gadolinium does not significantly aid in the T staging or differentiation of benign from malignant lymph nodes. The CRM, as well as presence of EMVI, is currently not part of the TNM staging but
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