Colon Polyps and the Role of Therapeutic Gastro-Intestinal Endoscopy
Hervé C. Boucard, MD. July 2011.
Brief history of Endoscopy. In the early 1900s, the first attempts to view inside the body with ‘lighted telescopes’ were made. The initial devi- ces were often fully rigid. The next major step forward was made by Basil Hirschowitz who invented a glass fiber for flexible endoscopes. The technology resulted in not only the first useful medical endoscope, but revolutionized other endoscopic uses and led to fiber optics (fig. 1).
In the 1930s, semi-flexible gastroscopes were developed. A fiber optic cable is simply a bun- dle of microscopic glass or plastic fibers that allows light to be transmitted through curved structures. Fiber optic cables are also replacing metal wires as the backbone of the world’s telecommunications infrastructure (Internet, phones, high definition TV etc).
Colorectal polyps and cancer (CRC). In the US, both the incidence and mortality from colo- rectal cancer have been slowly but steadily de- creasing. In 2010, it was estimated that 142,600 new cases of colon cancer would be diagnosed,
102,900 from the colon; the rest from the rectum. Annually, 51,370 Americans die of CRC, accounting for about 9% of all cancer deaths. Age is a major risk factor for colorectal cancer. Colon cancer a rare diagnosis before the age of 40. Incidence of this cancer rises sharply between 40 and 50 years of age.
The lifetime incidence of CRC in patients at average risk is about 5%. Ninety percent of cases occur after the age 50. In the US, CRC incidence is about 25 % higher in men than in women. Incidence is 20% higher in African Americans than in whites.
Globally, the incidence of CRC varies over 10- fold; the highest incidence rates in North America, Australia, and northern and western Europe. Developing countries have lower rates, particularly Africa and Asia. Geographic differ- rences appear to be attributable to the diet and the environment added to a background of genetically determined susceptibility. A high fiber diet (vegetable, rice etc) as opposed to a high fat diet seem to confer a significant degree of protection. In the US, the incidence and mor- tality rates are highest in African-Americans.
Colon polyps and risk of cancer. About two- thirds of colon polyps are adenomas. Adeno- mas are by definition dysplastic and thus have malignant potential. Nearly all colorectal can- cers arise from adenomas but only a small mi- nority of adenomas progress to cancer (<5 %). The time for development of adenomas to cancer is about 7 to 10 years giving ample of time for detection and resection.
Older age is a major risk factor for adenoma. Prevalence of adenoma ranges from 1 to 4% at age 20 to 30 but increases to 25 to 30 % by age 50. Autopsy studies revealed rates of 50 % by age 70. Abdominal obesity is a risk factor for adenomatous polyps and is a better predictor than body mass index (BMI) or waist circumference in both sexes.
Adenomatous polyps are more common in men. Large adenomas (≥9 mm) are more common in African-Amerian than Caucasians. Blacks have a higher risk of right-sided colonic adenomas and present with cancer at a younger age (<50 years of age) than Whites.
Colonoscopy is a great tool for detection and removal of polyps. Gastroenterologists dispose of a several ingenious tools for detection and elimination of polyps. Their armamentarium include the biopsy forceps, the snare with cautery apparatus, submucosal injection needles etc. Large polyps of several centimeters whether sessile or pedunculated can be safely removed with good hemostasis by the skillful endoscopist. Endoscopic baskets allow retrieval of the samples for pathology (fig. 2). Inadvertent bleeding can be successfully controlled with heating probes, epinephrine injection or endoclipping all done through the endoscope. As long as high grade dysplasia is not encountered by pathology, the vast majority of polyp can be safely obliterated endoscopically thus preventing laparotomy.
Sessile polyps pose a real challenge to the endoscopist. First they are often located at the right colon where the preparation is often suboptimal due to remnant stools. Besides, they tend to be of the villous type giving them a rapid propensity for frank dysplasia development and carcinoma. Last but not least, they are much harder to detect by standard techniques. The recommendations nowadays is that the endoscopist spend a minimum of 6 minutes during scope withdrawal to maximize polyps detection.
The eradication of adenomas is important to decrease cancer risk; this is evidenced by the decrease in the incidence of colorectal cancer in the US with widespread colon cancer screening. Colonoscopy is considered to be the optimal examination for the detection of adenomatous polyps but is far from perfect. One report eva- luated the colonoscopy miss rate determined by two same-day endoscopic examinations in 183 patients. Miss rate was found to be 27 % for adenomas <5 mm, 13 % for those 6 to 9 mm, and 6 % for adenomas >1 cm.
With the advent of colonoscopy colon cancer is becoming a fully preventable disease. The challenge remains to convince the people at risk to be screened. For now we should at least emphasize the proven protective roles of low fat and high in fruits vegetable and fiber diet.
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