Porth's Essentials of Pathophysiology, 4e

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Disorders of Gastrointestinal Function

C h a p t e r 2 9

Diagnosis andTreatment. Cancer of the colon may be detected with a high degree of reliability with barium enema or colonoscopy. Colonoscopy permits biopsy for pathologic confirmation. CT scans, pelvic magnetic resonance imaging (MRI), and ultrasonography may be used to determine the extent of the lesions and whether metastasis has occurred. The only recognized treatment for cancer of the colon and rectum is surgical removal. 65 Preoperative radiation therapy may be used and has in some cases demonstrated increased 5-year survival rates. Postoperative adjuvant chemotherapy may be used. Radiation therapy and che- motherapy are used as palliative treatment methods. The prognosis for persons with colorectal cancer depends largely on the stage of the cancer. Colorectal can- cer commonly is classified into four TNM (tumor, node, and metastasis) stages. 6,7 In this system, a stage I tumor is limited to invasion of the mucosal and submucosal lay- ers of the colon and has a 5-year survival rate of 90% to 100%. Stage IV (metastatic) tumors penetrate the serosa or adjacent organs and have a much poorer prognosis. Screening. The single most important prognostic indi- cator of colorectal cancer is the extent (stage) of the tumor at the time of diagnosis. The challenge, therefore, is to discover the tumors at their earliest stages. Among the methods used for early detection of colorectal can- cers are the digital rectal examination and the fecal occult blood test, usually done during routine physical examinations; x-ray studies using barium (e.g., barium enema); and flexible sigmoidoscopy and colonoscopy. 58,59 Almost all cancers of the colon and rectum bleed intermittently, although the amount of blood is small and usually not apparent in the stools. It therefore is feasible to screen for colorectal cancers using com- mercially prepared tests for occult blood in the stool. The sensitivity of fecal occult blood tests is improved by performing stool tests on three different occasions. Digital rectal examinations are most helpful in detecting neoplasms of the rectum. Rectal examination should be considered a routine part of a good physical examina- tion. Flexible sigmoidoscopy involves examination of the rectum and sigmoid colon with a hollow, lighted tube that is inserted through the rectum. The procedure is performed without sedation and is well tolerated. Approximately 40% of cancers and polyps are out of the reach of the sigmoidoscope, emphasizing the need for fecal occult blood tests. Polyps can be removed or tissue can be obtained for biopsy during the procedure. Colonoscopy provides a means for direct visualiza- tion of the rectum and colon. The colonoscope con- sists of a flexible, 4-cm–diameter glass fiber bundle that contains approximately 250,000 glass fibers and has a lens at either end to focus and magnify the image. Light from an external source is transmitted by the fiber-optic viewing bundle. Instruments are available that afford direct examination of the sigmoid colon or the entire colon. This method is used for screening persons at high risk for development of cancer of the colon (e.g., those with ulcerative colitis) and for those with symptoms. Colonoscopy also is useful for obtaining a biopsy and

SUMMARY CONCEPTS ■■ Disorders of the small and large intestines include inflammatory bowel disease, infectious enterocolitis, diverticular disease, appendicitis, disorders of motility, peritonitis, alterations in intestinal absorption, and colorectal cancer. ■■ The term inflammatory bowel disease is used to designate two inflammatory conditions: Crohn disease, which affects the small and large bowel, and ulcerative colitis, which affects the colon and rectum. Both are chronic diseases characterized by remissions and exacerbations of diarrhea, weight loss, fluid and electrolyte disorders, and systemic signs of inflammation. ■■ Enterocolitis includes viral (e.g., rotavirus) and bacterial (e.g., C. difficile and E. coli O157:H7) infections. ■■ Diverticular disease is a condition in which the mucosa and submucosa of the colon herniate through the muscularis layer, and diverticulitis, in which there is inflammation and gross or microscopic perforation of the diverticulum. ■■ Diarrhea, constipation, and irritable bowel syndrome represent disorders of intestinal food intolerance, drugs, or intestinal disease. Constipation or the infrequent passage of stools is commonly caused by failure to respond to the urge to defecate, inadequate fiber or fluid intake, weakness of the abdominal muscles, inactivity and bed rest, or pregnancy. Irritable bowel syndrome is characterized by a variable combination of chronic and recurrent intestinal symptoms, that are not related to a structural or biochemical abnormality. motility. Diarrhea or excessively frequent passage of stools can be caused by infectious organisms, for removing polyps. Although this method is one of the most accurate for detecting early colorectal cancers, it is not suitable for mass screening because it is expensive and time consuming and must be done by a person who is highly trained in the use of the instrument. It is recommended that persons at average risk for colonic adenomatous polyps or cancer should undergo colonoscopy every 10 years or alternative screening tests at periodically prescribed intervals beginning at age 50. 59 Persons who are members of high-risk groups, such as those with a family history of adenomatous pol- yps or disorders that predispose to colon cancer (e.g., ulcerative colitis), should undergo periodic surveillance more frequently.

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