Colorectal Carcinoma

General characteristics

Adenocarcinoma of the colon is the most common gastrointestinal tract malignancy and the second most common visceral cancer.

Aetiology

The conditions that predispose to the development of colon cancer include heredity, familial adenomatous polyposis, Gardner syndrome, Lynch syndrome, ulcerative colitis, and Crohn’s colitis.

Location

Cancers occur most often in the rectosigmoid colon, but right-sided cancers tend to occur in increasing frequency.

Morphology

Tumors may be polypoid, circumferential (“apple core”), or plaque-like.

Imaging

Good correlation is observed between gadoliniumenhanced fat-suppressed MRI techniques and surgical specimens for tumor size, bowel wall involvement, peritumoral extension, and lymph node detection (Shoenut et al. 1993). Malignant lymph nodes are usually not enlarged in gastrointestinal adenocarcinoma. However, the presence of more than five lymph nodes that measure smaller than 1 cm in a regional distribution related to the tumor correlates well with tumor involvement. All segments of the colon and the appendix are well shown on MR images. The combination of T2-weighted single-shot echo-train spin-echo and gadolinium-enhanced fat-suppressed SGE images result in the most reproducible image quality for the colon above the rectum. Rectal and colon cancers benefit from the combined use of gadolinium- enhanced fat-suppressed SGE and high-resolution T2-weighted echo-train spin-echo images. MR colonography employing a bowel cleansing preparation and administration of rectal water enema has been shown effective in demonstrating small polyps and tumors (Ajaj et al. 2003).

Contrast enhancement

Gadolinium-enhanced fat-suppressed SGE imaging is valuable in demonstrating perirectal tumor extension, regional lymph nodes, and seeding of peritoneal by tumor. This reflects the high-contrast resolution of this technique for detecting enhancing diseased tissue. Image acquisition of T2-weighted echo-train spin-echo or single-shot echo train-spin echo after the administration of gadolinium is commonly done when abdomen and pelvis studies are combined in one examination.

Differential diagnosis

As an additional benefit to a shortened MR examination, dependent, concentrated gadolinium in the bladder, which is low in signal intensity, may increase the conspicuity of high-signal intensity rectal tumor invasion of the bladder wall. Endorectal coil imaging permits differentiation of the anatomic layers of the rectal wall on T2-weighted fatsuppressed images. Local staging of rectal carcinoma also benefits from endorectal coil imaging.



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