Location and appearance of two example colorectal tumors
Colonoscopy being performed
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.
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.
Colon cancer with extensive metastases to the liver
Schematic overview of colonoscopy procedure
Relative incidence of various histopathological types of colorectal cancer. The vast majority of colorectal cancers are adenocarcinomas.
Polyp is identified.
Micrograph of colorectal adenocarcinoma, showing "dirty necrosis".
A sterile solution is injected under the polyp to lift it away from deeper tissues.
A diagram of a local resection of early stage colon cancer
A portion of the polyp is now removed.
A diagram of local surgery for rectal cancer
The polyp is fully removed.
Colon and rectum cancer deaths per million persons in 2012

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

- Colonoscopy

Bowel cancer may be diagnosed by obtaining a sample of the colon during a sigmoidoscopy or colonoscopy.

- Colorectal cancer
Location and appearance of two example colorectal tumors

10 related topics

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The three most common sites of intestinal involvement in Crohn's disease (left) compared to the areas affected by colitis ulcerosa (right).

Crohn's disease

Type of inflammatory bowel disease that may affect any segment of the gastrointestinal tract.

Type of inflammatory bowel disease that may affect any segment of the gastrointestinal tract.

The three most common sites of intestinal involvement in Crohn's disease (left) compared to the areas affected by colitis ulcerosa (right).
An aphthous ulcer on the mucous membrane of the mouth in Crohn's disease.
A single lesion of erythema nodosum
Endoscopic image of colon cancer identified in the sigmoid colon on screening colonoscopy for Crohn's disease
NOD2 protein model with schematic diagram. Two N-terminal CARD domains (red) connected via helical linker (blue) with central NBD domain (green). At C-terminus LRR domain (cyan) is located. Additionally, some mutations which are associated with certain disease patterns in Crohn's disease are marked in red wire representation.
Distribution of gastrointestinal Crohn's disease.
Endoscopic image of Crohn's colitis showing deep ulceration
CT scan showing Crohn's disease in the fundus of the stomach
Endoscopic biopsy showing granulomatous inflammation of the colon in a case of Crohn's disease.
Section of colectomy showing transmural inflammation
Resected ileum from a person with Crohn's disease

Bowel obstruction may occur as a complication of chronic inflammation, and those with the disease are at greater risk of colon cancer and small bowel cancer.

Checking for bowel cancer via colonoscopy is recommended every few years, starting eight years after the disease has begun.

Front of abdomen, showing the large intestine, with the stomach and small intestine in gray.

Large intestine

Last part of the gastrointestinal tract and of the digestive system in vertebrates.

Last part of the gastrointestinal tract and of the digestive system in vertebrates.

Front of abdomen, showing the large intestine, with the stomach and small intestine in gray.
Illustration of the large intestine.
Inner diameters of colon sections
Colonic crypts (intestinal glands) within four tissue sections. The cells have been stained to show a brown-orange color if the cells produce the mitochondrial protein cytochrome c oxidase subunit I (CCOI), and the nuclei of the cells (located at the outer edges of the cells lining the walls of the crypts) are stained blue-gray with haematoxylin. Panels A, B were cut across the long axes of the crypts and panels C, D were cut parallel to the long axes of the crypts. In panel A the bar shows 100 µm and allows an estimate of the frequency of crypts in the colonic epithelium. Panel B includes three crypts in cross-section, each with one segment deficient for CCOI expression and at least one crypt, on the right side, undergoing fission into two crypts. Panel C shows, on the left side, a crypt fissioning into two crypts. Panel D shows typical small clusters of two and three CCOI deficient crypts (the bar shows 50 µm). The images were made from original photomicrographs, but panels A, B and D were also included in an article and illustrations were published with Creative Commons Attribution-Noncommercial License allowing re-use.
Histological section.
Colonoscopy image, splenic flexure,
normal mucosa. You can see spleen through it : the black part
Micrograph of normal large instestinal crypts.
Anatomy of normal large intestinal crypts
Intestines
Colon. Deep dissection. Anterior view.

A significant indirect health consequence is that use of a standard adult colonoscope is difficult and in some cases impossible when a redundant colon is present, though specialized variants on the instrument (including the pediatric variant) are useful in overcoming this problem.

Bacteroides are implicated in the initiation of colitis and colon cancer.

Endoscopic image of a colon affected by ulcerative colitis. The internal surface of the colon is blotchy and broken in places. Mild-moderate disease.

Ulcerative colitis

Long-term condition that results in inflammation and ulcers of the colon and rectum.

Long-term condition that results in inflammation and ulcers of the colon and rectum.

Endoscopic image of a colon affected by ulcerative colitis. The internal surface of the colon is blotchy and broken in places. Mild-moderate disease.
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.
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).
Aphthous ulcers involving the tongue, lips, palate, and pharynx.
Pyoderma gangrenosum with large ulcerations affecting the back.
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.
H&E stain of a colonic biopsy showing a crypt abscess, a classic finding in ulcerative colitis
Colonic pseudopolyps of a person with intractable UC, colectomy specimen
Biopsy sample (H&E stain) that demonstrates marked lymphocytic infiltration (blue/purple) of the intestinal mucosa and architectural distortion of the crypts.

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

Diagnosis is typically by colonoscopy with tissue biopsies.

Micrograph showing inflammation of the large bowel in a case of inflammatory bowel disease. Colonic biopsy. H&E stain.

Inflammatory bowel disease

Group of inflammatory conditions of the colon and small intestine, Crohn's disease and ulcerative colitis being the principal types.

Group of inflammatory conditions of the colon and small intestine, Crohn's disease and ulcerative colitis being the principal types.

Micrograph showing inflammation of the large bowel in a case of inflammatory bowel disease. Colonic biopsy. H&E stain.
Associated loci pane. Pink genes are in IBD associated loci, blue are not.

Diagnosis is generally by assessment of inflammatory markers in stool followed by colonoscopy with biopsy of pathological lesions.

Many studies identified that microRNAs dysregulation involved in IBD and to promote colorectal cancer.

Sigmoidoscopy

Minimally invasive medical examination of the large intestine from the rectum through the nearest part of the colon, the sigmoid colon.

Minimally invasive medical examination of the large intestine from the rectum through the nearest part of the colon, the sigmoid colon.

A sigmoidoscopy is similar to, but not the same as, a colonoscopy.

However, although in absolute terms only a relatively small section of the large intestine can be examined using sigmoidoscopy, the sites which can be observed represent areas which are most frequently affected by diseases such as colorectal cancer, for example the rectum.

Polyp of sigmoid colon as revealed by colonoscopy. Approximately 1 cm in diameter. The polyp was removed by snare cautery.

Colorectal polyp

Polyp occurring on the lining of the colon or rectum.

Polyp occurring on the lining of the colon or rectum.

Polyp of sigmoid colon as revealed by colonoscopy. Approximately 1 cm in diameter. The polyp was removed by snare cautery.
Incidences and malignancy risks of various types of colorectal polyps.
Microvesicular hyperplastic polyp. H&E stain.
Microvesicular hyperplastic polyp. H&E stain.
Traditional serrated adenoma. H&E stain.
Gross appearance of a colectomy specimen containing two colorectal polyps and one invasive colorectal carcinoma
Micrograph of a tubular adenoma, the most common type of dysplastic polyp in the colon.
Micrograph of a sessile serrated adenoma. H&E stain.
Micrograph of a Peutz–Jeghers colonic polyp – a type of hamartomatous polyp. H&E stain.
Micrograph of a tubular adenoma – dysplastic epithelium (dark purple) on left of image; normal epithelium (blue) on right. H&E stain.
Micrograph of a villous adenoma. These polyps are considered to have a high risk of malignant transformation. H&E stain.
Paris classification of colorectal neoplasms.<ref>{{cite book|title=Colonoscopy and Colorectal Cancer Screening: Future Directions|author=Luis Bujanda Fernández de Piérola, Joaquin Cubiella Fernández, Fernando Múgica Aguinaga, Lander Hijona Muruamendiaraz and Carol Julyssa Cobián Malaver|contribution=Malignant Colorectal Polyps: Diagnosis, Treatment and Prognosis|year=2013|doi=10.5772/52697|isbn=9789535109495}} Creative Commons Attribution 3.0 License</ref>

Untreated colorectal polyps can develop into colorectal cancer.

Colorectal polyps can be detected using a faecal occult blood test, flexible sigmoidoscopy, colonoscopy, virtual colonoscopy, digital rectal examination, barium enema or a pill camera.

Scheme of digestive tract, with rectum marked

Rectum

Final straight portion of the large intestine in humans and some other mammals, and the gut in others.

Final straight portion of the large intestine in humans and some other mammals, and the gut in others.

Scheme of digestive tract, with rectum marked
The inside of a normal human rectum in a 70-year-old, seen during colonoscopy
Retroflexed view of the human rectum seen at colonoscopy showing anal verge
A digital rectal exam is conducted to investigate or diagnose conditions including of the prostate.
Arteries of the pelvis
Blood vessels of the rectum and anus
Cross-section microscopic shot of the rectal wall
Dog rectum cross-section (40×)
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).

Colonoscopy and sigmoidoscopy are forms of endoscopy that use a guided camera to directly view the rectum.

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

Blood smear showing iron-deficiency anemia, with small, pale red blood cells.

Anemia

Blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin.

Blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin.

Blood smear showing iron-deficiency anemia, with small, pale red blood cells.
Main symptoms that may appear in anemia
The hand of a person with severe anemia (on the left, with ring) compared to one without (on the right)
Figure shows normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a normal red blood cell with normal hemoglobin.
Peripheral blood smear microscopy of a patient with iron-deficiency anemia
A Giemsa-stained blood film from a person with iron-deficiency anemia. This person also had hemoglobin Kenya.

In the United States, the most common cause of iron deficiency is bleeding or blood loss, usually from the gastrointestinal tract. Fecal occult blood testing, upper endoscopy and lower endoscopy should be performed to identify bleeding lesions. In older men and women, the chances are higher that bleeding from the gastrointestinal tract could be due to colon polyps or colorectal cancer.

Modern CT scanner

CT scan

Medical imaging technique used in radiology (x-ray) to obtain detailed internal images of the body noninvasively for diagnostic purposes.

Medical imaging technique used in radiology (x-ray) to obtain detailed internal images of the body noninvasively for diagnostic purposes.

Modern CT scanner
Drawing of CT fan beam and patient in a CT imaging system
Computed tomography of human brain, from base of the skull to top. Taken with intravenous contrast medium.
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Bronchial wall thickness (T) and diameter of the bronchus (D)
Example of a CTPA, demonstrating a saddle embolus (dark horizontal line) occluding the pulmonary arteries (bright white triangle)
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Types of presentations of CT scans:
- Average intensity projection
- Maximum intensity projection
- Thin slice (median plane)
- Volume rendering by high and low threshold for radiodensity
Typical screen layout for diagnostic software, showing one volume rendering (VR) and multiplanar view of three thin slices in the axial (upper right), sagittal (lower left), and coronal planes (lower right)
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3D human skull from computed tomography data
Left image is a sinogram which is a graphic representation of the raw data obtained from a CT scan. At right is an image sample derived from the raw data.

It has more recently been used for preventive medicine or screening for disease, for example, CT colonography for people with a high risk of colon cancer, or full-motion heart scans for people with a high risk of heart disease.

CT scanning can perform a virtual colonoscopy with greater accuracy and less discomfort for the patient than a traditional colonoscopy.

Cards and bottle used for the Hemoccult test, a type of stool guaiac test

Fecal occult blood

Not visibly apparent (unlike other types of blood in stool such as melena or hematochezia).

Not visibly apparent (unlike other types of blood in stool such as melena or hematochezia).

Cards and bottle used for the Hemoccult test, a type of stool guaiac test
A LabCorp fecal occult blood immunoassay testing kit.
A positive traditional guaiac fecal occult blood test

Positive tests ("positive stool") may result from either upper gastrointestinal bleeding or lower gastrointestinal bleeding and warrant further investigation for peptic ulcers or a malignancy (such as colorectal cancer or gastric cancer).

In 2009 the American College of Gastroenterology (ACG) suggested that colon cancer screening modalities that are also directly preventive by removing precursor lesions should be given precedence, and prefer a colonoscopy every ten years in average-risk individuals, beginning at age 50.