Location and appearance of two example colorectal tumors
Endoscopic image of a colon affected by ulcerative colitis. The internal surface of the colon is blotchy and broken in places. Mild-moderate disease.
Scheme of digestive tract, with rectum marked
Longitudinally opened freshly resected colon segment showing a cancer and four polyps. Plus a schematic diagram indicating a likely field defect (a region of tissue that precedes and predisposes to the development of cancer) in this colon segment. The diagram indicates sub-clones and sub-sub-clones that were precursors to the tumors.
Classification of colitis, often used in defining the extent of involvement of ulcerative colitis, with proctitis (blue), proctosigmoiditis (yellow), left sided colitis (orange) and pancolitis (red). All classes extend distally to the end of the rectum.
The inside of a normal human rectum in a 70-year-old, seen during colonoscopy
Colon cancer with extensive metastases to the liver
Gross pathology of normal colon (left) and severe ulcerative colitis (right), forming pseudopolyps (smaller than the cobblestoning typically seen in Crohn's disease), over a continuous area (rather than skip lesions of Crohn's disease), and with a relatively gradual transition from normal colon (while Crohn's is typically more abrupt).
Retroflexed view of the human rectum seen at colonoscopy showing anal verge
Relative incidence of various histopathological types of colorectal cancer. The vast majority of colorectal cancers are adenocarcinomas.
Aphthous ulcers involving the tongue, lips, palate, and pharynx.
A digital rectal exam is conducted to investigate or diagnose conditions including of the prostate.
Micrograph of colorectal adenocarcinoma, showing "dirty necrosis".
Pyoderma gangrenosum with large ulcerations affecting the back.
Arteries of the pelvis
A diagram of a local resection of early stage colon cancer
Endoscopic image of ulcerative colitis affecting the left side of the colon. The image shows confluent superficial ulceration and loss of mucosal architecture. Crohn's disease may be similar in appearance, a fact that can make diagnosing UC a challenge.
Blood vessels of the rectum and anus
A diagram of local surgery for rectal cancer
H&E stain of a colonic biopsy showing a crypt abscess, a classic finding in ulcerative colitis
Cross-section microscopic shot of the rectal wall
Colon and rectum cancer deaths per million persons in 2012
Colonic pseudopolyps of a person with intractable UC, colectomy specimen
Dog rectum cross-section (40×)
Biopsy sample (H&E stain) that demonstrates marked lymphocytic infiltration (blue/purple) of the intestinal mucosa and architectural distortion of the crypts.
Microscopic cross-section of the rectum of a dog (400×), showing a high concentration of goblet cells in amongst the column-shaped lining. Goblet cells can be seen as the circular cells with a clear inner material (cytoplasm).

Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine).

- Colorectal cancer

Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum.

- Ulcerative colitis

Another risk factor is inflammatory bowel disease, which includes Crohn's disease and ulcerative colitis.

- Colorectal cancer

Complications may include abnormal dilation of the colon (megacolon), inflammation of the eye, joints, or liver, and colon cancer.

- Ulcerative colitis

Ulcerative colitis, one form of inflammatory bowel disease that causes ulcers that affect the rectum. This may be episodic, over a person's lifetime. These may cause blood to be visible in the stool. the cause is unknown.

- Rectum

Rectal cancer, a subgroup of colorectal cancer specific to the rectum.

- Rectum
Location and appearance of two example colorectal tumors

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Colonoscopy being performed

Colonoscopy

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Endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus.

Endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus.

Colonoscopy being performed
A container of PEG (polyethylene glycol or macrogol) with electrolyte used to clean out the intestines before certain bowel exam procedures such as a colonoscopy.
Schematic overview of colonoscopy procedure
Polyp is identified.
A sterile solution is injected under the polyp to lift it away from deeper tissues.
A portion of the polyp is now removed.
The polyp is fully removed.

It can provide a visual diagnosis (e.g., ulceration, polyps) and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions.

In most cases the positive result is just due to hemorrhoids; however, it can also be due to diverticulosis, inflammatory bowel disease (Crohn's disease, ulcerative colitis), colon cancer, or polyps.

The endoscope is then passed through the anus up the rectum, the colon (sigmoid, descending, transverse and ascending colon, the cecum), and ultimately the terminal ileum.