Diagnosis

The test of choice for the determination of the source of lower GI bleeding is colonoscopy. Adequate bowel preparation with an oral sulfate purge to clear the bowel of blood, clots, and stool increases the yield in diagnosing colonic bleeding sites. Angiography and technetium-labeled colloid or red blood cell scans may be of value if colonoscopy cannot be performed or if heavy bleeding prevents adequate visualization of the colon. However, the magnitude of bleeding required to show the bleeding site limits their usefulness. Sigmoidoscopy with air-contrast barium enema x-rays may be an alternative when colonoscopy is unavailable or if the patient refuses colonoscopy. If the initial sigmoidoscopy is negative, a colonoscopy must be performed. If both of these studies are negative, panendoscopy should be carried out.

Always consider the possibility of upper GI bleeding as a source of hema-tochezia. An aspirate from a nasogastric tube can help to make this determination. An aspirate that shows bile but not blood will help to confirm that the bleeding is from a lower GI source.

Etiologies Hemorrhoids

Hemorrhoids are dilated veins in the hemorrhoidal plexus of the anus. They are defined as "internal" if they arise above the dentate line and "external" if they arise below the dentate line; both can be the cause of hematochezia. Chronic-constipation, straining for bowel movements, pregnancy, and prolonged sitting (e.g., truck drivers) are risk factors. Along with bleeding, external hemorrhoids can cause pain, irritation, and a palpable lump. Internal hemorrhoids can cause bleeding and can prolapse through the anus. Conservative treatment with a high-fiber diet, stool softeners, and precautions against prolonged straining are usually successful. When necessary, various surgical procedures can be performed for definitive treatment.

Diverticular Disease

Diverticula are outpouchings of the colonic mucosa through weakened areas of the colon wall. They occur most often where blood vessels penetrate through the muscles of the colon. They are most often asymptomatic and found on endoscopy or bowel imaging studies. They can cause symptomatic, and occasionally massive, bleeding that is usually painless. Diverticular bleeding usually stops spontaneously. When the bleeding is extremely heavy or fails to stop, surgical resection of the affected portion of the colon may be necessary. Asymptomatic diverticulosis is managed with dietary modification, primarily a high-fiber diet.

Diverticulitis is a painful inflammation and infection of a diverticulum. Diverticulitis frequently causes left lower quadrant abdominal pain along with fever, nausea, diarrhea, and constipation. Perforation of a diverticulum resulting in peritonitis or intraabdominal abscess formation can be a complication. Diverticulitis is typically treated with bowel rest and antibiotics effective against gut flora. A combination of a quinolone and an agent for anaerobic organisms, such as metronidazole, is one commonly used regimen. In severe cases, or when perforation occurs, surgery may be indicated.

Inflammatory Bowel Disease

Ulcerative colitis and Crohn disease are the two primary diagnoses considered in the category of inflammatory bowel disease (IBD). Ulcerative colitis causes continuous inflammation of the large bowel, starting from the rectum and extending proximally. Severe disease can cause pancolitis, affecting the entire colon. Crohn disease causes areas of focal inflammation, hut can occur anywhere in the gastrointestinal tract. Both diseases can cause recurrent episodes of abdominal pain, diarrhea, weight loss, rectal bleeding, fistulas, and abscesses. The definitive etiology of IBD is not known, but these are autoimmune syndromes and a family history of IBD is a major risk factor. Along with GI symptoms, numerous extraintestinal manifestations may occur, most frequently arthritis. Other extraintestinal manifestations include sclerosing cholangitis, cirrhosis, fatty liver, pyoderma gangrenosum, and erythema nodosum. Ulcerative colitis is a significant risk factor for the development of colon cancer. Patients with ulcerative colitis require frequent surveillance colonoscopic examinations. IBD can be managed with symptomatic therapy, such as antidiarrheal medications, along with antiinflammatory medications (aminosalicylates, corticosteroids) given orally or as enemas, and immunosuppressive medications. Ulcerative colitis can be definitively treated with a total colectomy, which is usually reserved for severe pancolitis, failure to respond to medical therapy, or because of the risk of colon cancer.

Colon Neoplasms

Polyps are benign neoplasms of the colon. Hyperplastic polyps tend to be small, smooth growths found incidentally during endoscopy and are of no prognostic significance. Adenomatous polyps are benign growths that have a potential to become malignant. Listed in order of potential for becoming cancerous (from least to most), the three types of adenomas are tubular adenomas, tubulovillous adenomas, and villous adenomas. Larger polyps have a higher risk of causing bleeding and becoming malignant than smaller polyps. Polyps can be identified and removed during a colonoscopy.

Colon cancer is the second leading cause of cancer death in men and women. The risk of colon cancer increases with age, with a history of colon polyps, a family history of colon cancer or a personal history of ulcerative colitis. Any patient older than age 50 years who has lower GI bleeding must be evaluated for the presence of colon cancer. Because of the presence of premalignant lesions (polyps) that can be identified and removed in asymptomatic patients, colon cancer screening is recommended for all adults older than age 50, and at younger ages for those with increased risks. The treatment and prognosis of colon cancer depends upon the stage in which it is found. The Dukes System stages colon cancer from A to D, depending on the penetration through the bowel wall layer, the presence of lymph node spread, and distant metastases. Dukes A colon cancer has an excellent prognosis with surgical resection: Dukes D cancer is usually not curable and is treated with combinations of surgery, chemotherapy and radiation.

Diverticular bleeding occurs in 10-20% of cases of lower GI bleeding, with most cases being increased by NSAID or aspirin use. In diverticular disease, bleeding is often self-limited and ceases approximately 75% of the time, while recurring at a rate of approximately 38%. More common causes include hemorrhoids (59%), colorectal polyps (38-52%). diverticulosis (34-51%), colorectal cancer (8%), ulcerative colitis, arteriovenous malformations and colonic strictures. These percentages vary amongst age groups and most serious causes are expected in the elderly.

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