Causes and Symptoms
Diverticulosis is an acquired condition of the colon that involves a few to hundreds of blueberry-sized outpouchings of its wall, called diverticuli. Diverticular disease is usually manifested by the presence of multiple diverticuli that are at risk of causing abdominal pain, inflammation, or bleeding.
Although the wall of the colon is thin, microscopically it has four layers. The innermost layer is called the mucosa. Its main function is to absorb fluids from the substance entering the colon, turning it into a semisolid material called feces. Outside the mucosa is the submucosa, a layer that contains blood vessels as well as nerve cells that control the functions of mucosal cells. Outside the submucosa is the muscularis, which contains muscle cells that are able to contract, pushing feces along the colon and eventually out through the rectum. Outside the muscularis is the serosa, which forms a wrap around the colon and helps prevent infections in this organ from spreading beyond its walls.
The diverticuli that form in the colon are not true diverticuli, in that the entire wall is not present in the outpouching. Only the mucosal and submucosal layers pouch out through weakened areas in the muscularis layer. When examined by the naked eye, however, it appears as if the entire wall of the colon is involved in the tiny outpouching. The mucosa bulges out in the part of the colonic wall that is weakened; this is where arteries penetrate through clefts in the muscularis.
The large intestine begins with the cecum, which is connected to the small intestine. The cecum is a pouch leading to the colon, whose components are the ascending, transverse, descending, and sigmoid colon. The sigmoid colon leads to the rectum, which is connected to the outside of the body by the anal canal. Although diverticuli can appear at a variety of locations in the
gastrointestinal (GI) tract, they are usually located in the colon, most commonly in the sigmoid colon.
The most common form of diverticulosis is called spastic colon diverticulosis, which is a condition involving diverticuli that develop when the lumen (cavity) of the sigmoid colon is abnormally narrowed. Since the circumference of the colon alternately narrows and widens along its length, muscle contractions may result in local occlusions of the lumen at the narrowed sections. Occlusion may cause the lumen of the colon to become multiple, separate chambers. When this happens, the pressure within the chambers can increase to the point where the mucosa herniates out through small clefts in the muscularis, creating diverticuli.
Most people with diverticulosis never notice it. When abdominal pain related to painful diverticular disease develops, it is felt in the lower abdomen and may last for hours or days. Eating usually makes it worse, whereas passing gas or having a bowel movement may relieve it.
Besides causing abdominal pain, diverticuli may cause rectal bleeding, which may vary from mild to life threatening. Usually, there is a sudden urge to defecate followed by passage of red blood, clots, or maroon-colored stool. If the stool is black, the bleeding is probably from the upper GI tract.
Since the colon may be studded with multiple diverticuli, and the bleeding may stop by the time of evaluation, it is often difficult to tell which one bled. Diverticulosis is most common in elderly people, who may have other conditions of the colon that are associated with bleeding. Therefore, it is often impossible to confirm that the cause of bleeding was diverticular disease—even if the colon is lined with hundreds of diverticuli.
What is most important is to establish what part of the GI tract is bleeding. To find out if the bleeding could have come from the upper GI tract, a tube is passed through the nose into the stomach, and the contents are aspirated. If blood is not present, this suggests lower GI bleeding. In addition, the esophagus, stomach, and upper small intestine can be visualized with a flexible, snakelike instrument called an endoscope to exclude a source such as a bleeding ulcer.
It is more difficult to examine the lower GI tract. The simplest procedure is anoscopy, by which the physician can examine the inside of the anal canal for hemorrhoids. Proctosigmoidoscopy, a procedure similar to endoscopy, offers a view of the rectum and part of the sigmoid colon. It may reveal diverticuli or other lesions such as a bleeding growth called a polyp. Colonoscopy is most easily performed after bleeding has stopped. It requires cleaning out the contents of the colon and then inserting a long, flexible instrument called a colonoscope all the way to the cecum. The entire lining of the colon can be visualized while withdrawing the colonoscope.
Angiography
is a test done in the radiology department; it involves injecting dye into the vessels that lead to the colon. If there is active bleeding, it can help localize the source. Even if the bleeding has stopped, this procedure can sometimes identify abnormal blood vessel formations suggestive of cancer or a blood vessel abnormality called angiodysplasia.
Between 10 and 25 percent of people with diverticulosis suffer from one or more episodes of diverticulitis, which is an inflammatory condition that may progress to an infection. Initially, feces may become trapped and inspissated (thickened) in a diverticulum, irritating it and leading to inflammation. Inflammation is a tissue response to injury that involves local reactions that attempt to destroy the injurious material and begin the healing process. It is usually the first step in the body’s attempt to prevent infection and involves the migration of white blood cells out of blood vessels and into tissues, where they begin to fight off bacteria. The white blood cells release enzymes that cause tissue destruction. Because it is thin, the wall of the diverticulum may develop a tiny perforation.
Feces are made up of waste material and bacteria that normally do not cause problems when confined within the lumen of the colon. When a diverticulum perforates, however, they travel outside the colon and into other regions such as the peritoneal cavity, causing an infection. This infection along the outside of the colon is often limited, because many adjacent structures are able to wall off the bacteria, limiting their ability to extend through the peritoneal cavity. Although they become sealed off, they often form a pus-filled lesion called an abscess.
Fever and abdominal pain are the most common symptoms of diverticulitis. The fever may be high and associated with shaking chills. The pain is often sudden in onset, is often continuous, and may radiate from the left lower abdomen to the back. Laboratory findings usually include an elevated white blood cell count, a nonspecific finding that occurs with a variety of infections.
Radiographic studies are helpful for diagnosing and assessing the severity of diverticulitis. For example, a computed tomography (CT) scan can detect diverticuli or a thickening of the bowel wall associated with diverticulitis and can help assess whether abscesses are present.
Treatment and Therapy
There are two treatment goals in treating uncomplicated, painful diverticular disease: prevention of further development of diverticuli and pain relief. It is important to understand that the pressure that is able to develop inside the lumen of the colon is inversely related to the radius of the lumen. Therefore, if the lumen’s radius can be increased, the pressures within the lumen will lessen, theoretically decreasing the chance of diverticuli formation. One key to increasing the radius of the lumen of the colon is to increase the bulk of the stool by the addition of dietary
fiber.
A Western diet tends to be high in fiber-free animal products, and many foods that would ordinarily contain fiber, such as bread, lose much of their fiber during processing. This low-fiber diet may contribute to diverticulosis, which is prevalent in countries that have low-fiber diets. The typical American diet contains an average of ten to fifteen grams of fiber per day, whereas diets from regions such as Africa and Asia contain significantly more fiber. A high-fiber diet can increase stool bulk by 40 to 100 percent. Fiber adds bulk to the stool because it acts like a sponge, retaining water that would normally be reabsorbed by the colonic mucosa. Fiber also increases stool bulk because 50 to 70 percent of the fiber is degraded by the bacteria in the colon, and the products of degradation attract water by a process called osmosis.
The main fibers that increase stool bulk are the water-insoluble fibers, such as cellulose, hemicellulose, and lignin; they are derived from plants such as vegetables and whole-grain cereals. Diets high in these fibers have been shown to decrease the intraluminal pressure in the sigmoid colon as well as to relieve the pain associated with uncomplicated diverticular disease. Some research has suggested that adding ten to twenty-five grams per day of coarse, unprocessed wheat bran to various liquid and semisolid foods may provide the best results. The sudden addition of large amounts of bran to one’s diet, however, may cause bloating. Commercial preparations such as methylcellulose may be better tolerated during the first few weeks of therapy; their use may then be tapered off as bran is added to the diet. There are also various antispasmodic drugs available for inhibiting the muscle spasms of the colon, but many are not very effective for decreasing symptoms.
For diverticular bleeding, the most effective therapy is patience. Most episodes stop on their own, and conservative treatments such as maintaining the patient’s blood volume with intravenous fluids and possibly performing blood transfusions are all that is necessary. In those patients with continued active bleeding and in whom the source of the bleeding can be identified with angiography, a drug called
vasopressin may be administered into the artery over several hours. This causes constriction of the vessel and stops bleeding most of the time. Once the vasopressin is stopped, however, patients may resume bleeding.
If vasopressin fails, surgery may be necessary. Surgery is most often successful if the bleeding site has been well localized before the operation. In that case, only the involved segment of the colon needs to be removed. If the bleeding site cannot be identified, it may be necessary to remove a majority of the colon; this procedure is associated with a higher rate of postoperative complications.
Diverticulitis that warrants hospitalization is initially treated with intravenous antibiotics for seven to ten days. Antibiotics help prevent many patients from needing surgery. Most of those who respond to antibiotics will not have future attacks severe enough to warrant hospitalization.
Other measures may be necessary for the care of someone with diverticulitis, because the inflammation around the colon may be associated with problems such as narrowing of the bowel lumen to the point where it causes a partial or complete colonic obstruction. In this case, nothing should be given by mouth, and a tube should be passed through the nose into the stomach in order to suck out air and the stomach contents. This suction helps to reduce the amount of material that can pass through the colon and worsen the dilation of the colon that occurs proximal to the obstruction.
If the fever persists for more than a few days, the diverticulitis may be associated with complications. One complication is the formation of a large
abscess outside the colon, which may be detected by a CT scan. An abscess has a rim around it that makes it difficult for antibiotics to penetrate the liquid center. If it does not go away despite antibiotic therapy, surgery may be necessary. If the abscess is small, it is possible to remove the involved segment of bowel and reattach the two free ends. If the abscess is very large, it may be necessary first to drain the abscess and then to cut across the colon proximal to the diseased segment, attaching the free end of the proximal segment to the abdominal wall, a procedure called a diverting colostomy. Later, the diseased segment of colon can be removed, and the remaining two free ends of colon can be joined. Another option is to drain the abscess with the aid of visual guidance by the CT scan and then operate on the colon. Draining the abscess in this manner helps get the infection under control before surgery is performed. Other indications for surgery in diverticulitis include complications such as a persistent bowel obstruction. In this case, it is often necessary to use a two-stage approach rather than cure the problem in one operation.
Another complication of diverticulitis is a generalized infection of the peritoneal cavity, called
peritonitis. Surgery for peritonitis involves removing the leaking segment of bowel and attaching the remaining two free ends of the colon to the abdominal wall. In addition, the peritoneal cavity is rinsed with a sterile solution in an attempt to clean out the contaminating materials.
Diverticulitis may also be complicated by the presence of a perforation of a diverticulum leading to a fistula, an abnormally existing channel connecting two hollow organs. When there is a fistula between the colon and the bladder, stool can travel into the bladder. The bacteria in the stool can cause severe, recurrent urinary tract infections. Another symptom is that bowel gas gets into the bladder; when the patient urinates, there is an intermittent stream because of colonic gas being passed along with the urine. When a fistula exists, it is necessary to remove the diseased segment of colon, the fistula tract, and a small portion of the bladder where the tract entered it.
Even if a patient with diverticulitis seems to improve and is able to return home from the hospital without needing surgery, there is still a chance that surgery will be necessary in the future. Surgery may be needed if the patient continues to have repeated, severe attacks of diverticulitis or if a fistula between the colon and bladder causes recurring urinary tract infections. Another reason for surgery is persistent partial colonic obstruction and no possibility of inspecting the narrowed region of colon to exclude a constricting cancerous lesion as the cause of the obstruction.
Perspective and Prospects
Diverticuli are quite common in the United States and other countries in which much of the population tends to eat processed, low-fiber foods. Although residents of countries where a high-fiber diet is common tend to have a low prevalence of diverticulosis, their risk of developing this disease increases within ten years of moving to a country with a low-fiber diet. The prevalence of diverticulosis and diverticulitis appears to be increasing. For example, before 1900, colonic diverticuli were considered a curiosity in the United States, whereas by the early twenty-first century, they were found in more than half of Americans over the age of sixty. There are a few possible explanations for why this increasing prevalence is seen.
First, the change in the American diet probably plays a large part in the pathogenesis of diverticular disease. Fiber consumption may have fallen off by as much as 30 percent during the twentieth century. Many people in the United States eat foods such as quick-cooking rice, highly processed cereals, and processed flour, all of which contain less fiber than their unprocessed counterparts. In addition, the population tends to eat more fats and proteins and fewer carbohydrates. Many fibers are from food sources rich in carbohydrates and are carbohydrates themselves.
The increasing prevalence of diverticular disease may also be attributable to the changing survival pattern. The average life expectancy in the United States rose significantly over the course of the twentieth century, and the proportion of people over sixty-five has likewise risen. Thus, the American population is not only growing but also getting older. Since diverticulosis is seen in increasing frequencies with aging, it is understandable that more of it was seen in the late twentieth century and early twenty-first century than during the early twentieth century.
Another reason for the increase in the prevalence of diverticular disease could be improvements in detection. Now it is detected not only at autopsy but also by barium enema, during sigmoidoscopy, and during surgery. Thus, there are more opportunities for discovering diverticulosis.
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