Colonic diverticulosis is among the most common diseases in developed Western countries. In the United States, diverticulosis occurs in approximately one third of the population older than age 45 and in up to two thirds of the population older than 85 years,^1,2 and it also affects a significant proportion of younger adults.

Definition and causes

A diverticulum is a saclike protrusion in the colonic wall that develops as a result of herniation of the mucosa and submucosa through points of weakness in the muscular wall of the colon. The colonic diverticulum is a false or pulsion diverticulum-that is, it does not contain all layers of the colonic wall. Diverticulosis indicates the presence of multiple diverticula and generally implies an absence of symptoms (Fig. 1). Diverticular disease implies any clinical state caused by diverticula, including hemorrhage, inflammation, or their complications. Diverticulitis describes the presence of an inflammatory process associated with diverticula. Its pathogenesis is attributed to genetic and environmental factors (Box 1).

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Prevalence

The actual prevalence of diverticulosis is difficult to measure because most individuals are asymptomatic. Comparisons of the earliest and most recent autopsies and barium enema studies have indicated that the worldwide prevalence is increasing over time (Box 2).^1,3,4

Studies so far include barium examinations and necropsy series. These may be misleading for determining the actual prevalence rate, however, mainly because barium studies may overestimate the prevalence of diverticulosis in people who have been referred for gastrointestinal (GI) symptoms, and necropsy series may either overestimate the frequency of diverticula in older age groups or miss the presence of small diverticula in younger populations.^5,6 Whether these findings are the results of increased numbers of older individuals in the population, increased screening, or an actual increase in prevalence is unknown. Younger patients presenting earlier than age 40 years have a prevalence rate of 5% and are more commonly male.^7-9

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Pathophysiology

Colonic diverticulosis in general is an acquired disease, developing as mucosal and submucosal herniations through the circular muscle layer at vulnerable weak points of the colonic wall. Diverticula are covered only by serosa, and tend to develop at four well-defined points around the circumference of the colon, where the vasa recta penetrate the muscular layer.^10,11 These vessels enter the colonic wall on either side of the mesenteric teniae and on the mesenteric border of the two antimesenteric teniae. Diverticula do not develop in the rectum, presumably because of the coalescence of the teniae with the longitudinal muscle layer that marks the junction between the sigmoid colon and the rectum. In the colon, the presence of anatomic and physiologic changes contributes to the development of diverticula (Box 3). Mycosis, a set of findings consisting of the thickening of the muscular layer, shortening of the teniae, and luminal narrowing, is found in most patients with sigmoid diverticula.

The mechanical features of the colonic wall change with increasing age.^12,13 Combined barostat-manometry studies of the entire colon have demonstrated that compliance is lowest in the sigmoid and descending colon and greatest in the transverse and ascending colon.¹³ This difference in mechanical properties between the right and left sides might partly account for the left-sided predominance of diverticulosis.¹⁴

Structural components of the extracellular matrix of the colonic wall, including collagen, elastin, and proteoglycans, are likely to be important in maintaining the strength and integrity of the colonic wall.^15,16 Changes in these components of the bowel wall, such as damage and breakdown of mature collagen, and consequently its immature synthesis can lead to a change in bowel consistency.¹⁷ These changes may be related to a genetic predisposition such as that seen in Ehlers-Danlos and Marfan’s syndromes, which may be responsible for the occurrence of diverticula at an early age, or to the natural course of the aging process itself. In one study, it has been reported that collagen fibrils in the left colon are smaller and more tightly packed than those in the right colon with increasing age, and that this difference is accentuated in diverticular disease.¹⁶

The thickening of longitudinal and circular muscles in diverticular disease is neither hyperplastic nor hypertropic, but appears to be related to a contractile state. An increase in the number of elastic fibers has been observed only in the longitudinal muscle.¹⁸ It has been suggested that this process is responsible for longitudinal contraction, with subsequent thickening of both muscle layers.¹⁸ All these changes, along with elastin deposition in the teniae coli, lead to an irreversible state of contracture, with substantial bowel shortening, which may result in decreased resistance of the colon wall to persistent intraluminal pressure.¹⁹

In addition to other predisposing factors, diverticula are believed to develop as a result of elevated intraluminal pressure generated by tonic and rhythmic contractions, resulting in segmentation. If contractions occur relatively close to each other and form an enclosed space, pressure within that intervening segment of colon may exceed 90 mm Hg. However, segmentation on its own separates the colonic lumen into a series of chambers, with each having a different amount of pressure that is closely related to the chamber’s diameter. These isolated increases of intraluminal pressure are believed to predispose to herniation through the previously mentioned weak points of the colon.

The fiber content of the diet plays a large role in the pathogenesis of diverticular disease. Fiber has been found to be protective. Most fiber in the human diet is of plant origin and this type of fiber binds water and salt in the colon, leading to bulkier and more voluminous stools. Therefore, fiber decreases the frequency of contractions and prevents an exaggerated form of segmentation.^6,20,21 In addition, dietary fiber influences the content of colonic bacterial flora, forms the main substrate for bacterial carbohydrate fermentation, and produces energy-yielding substrates—short-chain fatty acids—for growth and maintenance of colonic cellular function. Consequently, a fiber-deficient diet increases the chances of intense, more frequent segmentation, thus predisposing to herniation of mucosa by allowing isolated increases of intraluminal pressure.^6,22

After the development of colonic diverticula, a spectrum of inflammatory changes or bleeding caused by the traumatic injury to penetrating vessels may occur.^20,21Changes within these vessel walls, such as eccentric intimal thickening and thinning of the media of the vessel facing the bowel lumen, result in segmental weakness of these vessels and render them vulnerable to injury and bleeding.

The term diverticulitis represents a spectrum of inflammatory changes that ranges from localized subclinical inflammation to generalized peritonitis, with free perforation (Fig. 2). In turn, this leads to hyperplasia of the lymphoid tissue within the mucosa at the base of the diverticulum, one of the earliest signs of diverticulitis. Inflammation usually begins at the apex of the diverticulum and seldom involves the neck or mucosa proximal to the neck. However, there is active inflammation of the pericolic and mesenteric fat, with peridiverticular abscess formation. These peridiverticular abscesses often involve areas of subserosa and are closely related to the outer aspect of the muscularis propria; they can spread circumferentially and longitudinally and may be responsible for the pathologic picture of diverticular colitis. Longitudinal tracking, especially, may result in fissuring, along with the lymphoid aggregates, which resembles the distinctive feature of colonic colitis in Crohn’s disease.²³ This may cause misinterpretation of the pathologic study of the specimen. Therefore, the differential diagnosis of these two conditions in terms of pathologic interpretation of the resected specimen is important. Persistent localized inflammation after diverticular rupture results in a phlegmon, a thickened, firm segment of bowel wall, which ultimately may manifest as acute or subacute large bowel obstruction. If left untreated or treated inadequately, it may result in extensive fibrosis around the affected segment of the colon, giving it a mass appearance indistinguishable macroscopically from that of a neoplasm.

Another pathologic entity that may be encountered during progression of the disease, with recurrent attacks of diverticulitis, is the formation of a localized abscess with chronic inflammation and involvement of other neighboring luminal organs, such as the bladder, small and large bowel loops, uterus, and vagina. Fistulae may develop within this contained area, between involved segment(s) of colon and these organs. Fistulae occur in 2.4% to 20% of cases; 65% of these fistulae are colovesical and 20% are colovaginal fistulae.^24-26

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Signs and symptoms

Most people with uncomplicated colonic diverticulosis are asymptomatic. A small fraction of these patients may have troublesome symptoms, such as colicky abdominal pain, bloating, flatulence, or altered bowel habit. The symptoms characteristically disappear after defecation or passage of flatus. On clinical examination, they may have tenderness in the left iliac fossa with no signs or symptoms of peritonitis or systemic illness, and all laboratory values may be within normal limits. The clinical picture of symptomatic uncomplicated diverticulosis often overlaps with that of irritable bowel syndrome (IBS), because these two clinical entities are usually diagnosed after other pathologies are excluded. IBS-type symptoms are independent of the presence or absence of diverticulosis on double-contrast barium enema studies. Bleeding alone can sometimes be the only sign of diverticulosis.²⁷

Signs and symptoms of acute diverticulitis may vary from local findings and manifestations to a wide variety of clinical pictures, with signs and symptoms of intra-abdominal sepsis, depending on the stage of disease (Box 4).

Patients with acute uncomplicated diverticulitis classically present with left-sided lower abdominal pain, fever, and leukocytosis.²⁸ The site of pain often depends on the segment of colon affected. Right-sided symptoms may occur in the presence of right-sided diverticulosis, as well as in redundant sigmoid colon lying on the right side of the abdomen. Patients with left-sided pain may also have right-sided symptoms. Other common manifestations are frequently related to GI disturbances, with alteration in bowel habits, constipation, either alone or alternating with bouts of diarrhea, anorexia, and nausea and vomiting. Urinary symptoms such as dysuria, frequency, and urgency may develop in a minority of patients, probably because of the proximity of the bladder to the inflamed sigmoid colon. In acute presentations, fever is almost always present, but high fever must suggest the possibility of advanced disease and sepsis from generalized peritonitis caused by perforation and spreading of inflammation in the peritoneum.

Abdominal findings reflect the severity and localization of the disease. In cases of diffuse peritonitis, generalized tenderness, involuntary guarding, or decreased or absent bowel sounds are noted. Severe abdominal distention with nausea and vomiting suggests bowel obstruction. The presence of pneumaturia and fecaluria signifies the presence of a colovesical fistula.

Immunocompromised and immunosuppressed patients constitute the most important group needing special attention in diagnosis and treatment. This patient group may lack a normal inflammatory response and present with minimal classic signs and symptoms, which may delay the diagnosis and treatment. This may result in sepsis and death. It is preferable to operate semielectively on these patients during the first episode of their initial hospitalization.

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Diagnosis

The initial assessment of patients with suspected acute diverticulitis is comprised of a thorough history and physical examination, including abdominal, rectal, and pelvic examinations. Useful initial examinations may include a complete blood cell count, urinalysis, and flat and upright abdominal radiography. If the clinical picture is clear enough to diagnose diverticulitis, no other tests are indicated.¹ When the diagnosis is in question, other tests such as computed tomography (CT), water-soluble contrast enema, cystography, endoscopy, and ultrasound may be performed. The differential diagnosis of acute diverticulitis should also be considered,²⁹ not only during examination of the patient but also while ordering the tests (Box 5). In particular, the differential diagnosis of colorectal cancer, as well as the detection of its possible coexistence, is important.^30,31 A barium enema examination should be avoided in acute presentations in patients with suspected acute diverticulitis and localized peritoneal signs because of a possible extravasation of barium into the peritoneal cavity, which can increase the morbidity and mortality related to barium-induced chemical peritonitis.³¹ In the emergency setting, water-soluble enemas are safer.

Abdominal ultrasound, with a sensitivity of 84% to 98% and a specificity of 80% to 97%, is a noninvasive screening tool with the potential drawback of the interpretation of the study, which may differ from one examiner to another.^32,33 It is helpful, especially in female patients, to exclude pelvic and gynecologic pathology. CT, with a sensitivity of 69% to 95%, a specificity of 75% to 100%, and a low false-positive rate, is generally superior to contrast studies.^30,34-36 CT with triple contrast—oral, rectal, and IV contrasts—is being used more frequently as the initial imaging study, especially in the acute setting, particularly whenever moderately severe disease or abscess is anticipated. In addition to the identification of complications such as phlegmon, abscess, adjacent organ involvement and distant septic complications, it also is a useful therapeutic tool for percutaneous drainage of intra-abdominal abscesses, providing the opportunity to downstage the intra-abdominal pathology so that it can be treated with a single-stage surgical procedure. The positive predictive value for diverticulitis by CT scanning is 73% for the presence of sigmoid diverticula, 88% for pericolic inflammation, 85% for wall thickness of 7 to 10 mm, and 100% for wall thickness more than 10 mm.³⁴ Severity staging by CT scanning may allow not only the selection of patients most likely to respond to conservative treatment, but may also predict the risk of failure of medical therapy and of secondary complications after initial conservative treatment. The incidence of subsequent complications is highest in patients with severe disease on initial CT.^37-39 CT is not useful in differentiating cancer from diverticulitis and must be supplemented by contrast enema studies or endoscopy. Although endoscopy is rarely indicated in an acute setting, if required, it should be done with gentle and cautious insufflation and manipulation because of the risk of perforation of an acutely inflamed colon, either by insufflation of air or by the instrument itself. It can be performed more safely after the patient recovers from the acute attack.

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Treatment

Medical Treatment

Complicated diverticulitis refers to acute diverticulitis accompanied by abscess, fistula, obstruction, or free intra-abdominal perforation. In the absence of complications and systemic signs and symptoms, patients with mild abdominal tenderness may be treated conservatively. Conservative treatment typically includes dietary modification and oral or IV antibiotics. This has been shown to be successful in 70% to 100% of patients.^37,38,40

Uncomplicated diverticulitis may be managed in the outpatient setting with dietary modification and oral antibiotics for those without fever, excessive vomiting, or marked peritonitis, as long as there is the opportunity for follow-up. If these conditions are not met or the patient fails to improve with outpatient therapy, hospital admission is required.

Antibiotic selection should be based on appropriate coverage for gram-negative rods and anaerobic bacteria.⁴¹ Conservative treatment will resolve acute diverticulitis in 85% of patients, but approximately one third will have a recurrent attack, often within a year.^5,42,43

After recovery from the first episode, use of fiber prevents recurrence in more than 70% of patients.^44,45 Immunosuppressed or immunocompromised patients are more likely to present with perforation and fail medical treatment.^41,42,46

Approximately 15% of patients develop pericolonic or intramesenteric abscess.^47,48 Abscesses smaller than 2 cm in diameter may resolve with antibiotic treatment without any further intervention, whereas larger abscesses may require percutaneous drainage. This may prevent an emergency operation and multistaged surgeries involving the creation and closure of stoma.^42,48,49

After resolution of the initial acute attack, the colon should be thoroughly evaluated with colonoscopy or contrast enema radiography.

Surgical Treatment

Surgical treatment of the disease can be evaluated emergently or electively, based on the stage of the disease and clinical presentation. Emergent sigmoid colectomy is required for patients with the following:

• Diffuse peritonitis
• Failure of conservative treatment
• Persistent sepsis despite percutaneous drainage
• Very low threshold, immunosuppressed, and immunocompromised patients who are likely to fail medical treatment and present with perforation.

Intraoperative surgical options are based on the status of the patient and the severity of intra-abdominal contamination (Hinchey classification; Box 6 and Figs. 3 to 6).⁵⁰ The desired surgical option is resection of the diseased segment with primary anastomosis, with or without intraoperative lavage or resection, and anastomosis with a temporary diverting ileostomy (Figs. 7 and 8). In advanced stages of peritonitis, Hartmann’s procedure (sigmoid colectomy, end colostomy, and closure of the rectal stump; Fig. 9) is the preferred operation, but it has been shown that the closure operation (Hartmann’s reversal) is not only technically challenging, but may be also associated with significant postoperative morbidity and mortality.⁵¹

The decision for elective colectomy after recovery from acute diverticulitis should be made on a case by case basis. After the first attack, about one third of the patients will have a later, second attack. After the second attack, another one third of patients will have another attack.^40,42 Factors affecting decision making for elective surgery include the following:

• Age
• Medical condition of the patient
• Frequency, persistence, and severity of the attacks
• CT-graded severity of the attack as a predictor of failure of medical treatment and possible risk of secondary complications
• Inability to exclude carcinoma.
• Conservative treatment of a complicated diverticulitis attack

There is no clear consensus regarding two widely debated points in management. First, the number of attacks of uncomplicated diverticulitis is not necessarily a determinant for appropriateness of surgery, because it has been shown that elective surgery after recovery from uncomplicated episodes might not decrease the likelihood of later emergency surgery or overall mortality.^40,46,52-54Second, patients younger than 50 years may have a higher cumulative risk for recurrent diverticulitis; however, whether they are at increased risk of complications or recurrent attacks remains debatable.^{5,28,40-42,54}

There are several important points regarding surgical technique. From a technical standpoint, the resection should be carried proximally to the compliant bowel and extend distally to the upper rectum. After sigmoid colectomy, an important predictor of recurrence is a colosigmoid rather than colorectal anastomosis. The proximal margin of resection should be in an area of pliable colon without hypertrophy or inflammation. Resection of the diseased colon must be the desired goal, along with removal of the entire thickened colonic segment(s) but not necessarily all the proximal diverticula-bearing colon. Laparoscopic colectomy is appropriate in select patients and has advantages over open laparotomy, including less pain, smaller incisions, and shorter recovery. There is no increase in early and late complications^55,56 and cost and outcome are comparable with those of open resection.⁵⁷

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Prevention

Prevention can be achieved by elimination of the factors involved in the pathogenesis of this disease (see Box 1). Increasing the proportion of fiber in the diet, along with an increase in fluid intake, will help keep more diverticula from forming and also will help keep the existing condition from worsening. Additionally, alteration of lifestyle by weight reduction and exercise can limit the contribution of other causative factors.

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Special circumstances

There are special circumstances in which the general recommendations for the diagnostic workup and treatment of diverticulitis may not apply. These are closely associated with the presence of factors such as manifestation of the disease, patient’s response to the disease, and treatment.

Diverticulitis in Young Patients

Diverticular disease is relatively uncommon before the age of 40 years and constitutes only 2% to 5% of the total number of patients in multiple large studies.^58,59 Diverticular disease in the younger age group occurs more commonly in men, with obesity (84%-96%) being a major risk factor.^60,61 There is ongoing controversy not only about the nature and course of the disease in this younger patient population, but also about the timing of the operation.^62-66 The disease trend in this patient group is toward more recurrence and an increased incidence of poor outcomes, ultimately requiring surgery.⁶⁷ This might be related to the fact that younger patients have a longer life expectancy, which increases the possibility and risk of subsequent episodes and related complications. Therefore, surgery may be often regarded as the treatment of choice for younger symptomatic patients.

Diverticulitis in Immunocompromised Patients

Conditions that represent an immunocompromised state include severe infection, steroids, diabetes mellitus, renal failure, malignancy, cirrhosis, and chemotherapy or immunosuppressive therapy. Although the incidence of diverticulitis does not appear to be increased in this population, the complications and sequelae of the diverticulitis are more severe. This group of patients may lack a normal inflammatory response and present with minimal or subtle signs and symptoms, which may delay the diagnosis and treatment. There is an increased rate of free perforation (43% vs. 14% in immunocompetent patients), increased need for surgery (58% vs. 33%), and increased postoperative mortality (39% vs. 2%).^68,69 Specifically, it is preferable to operate on transplant patients, immunocompromised patients, and patients under immunosuppression semielectively during the first episode of initial hospitalization. Primary resection with proximal diversion is the desired operation and should be attempted, whenever possible.

Recurrent Diverticulitis after Resection

Recurrent diverticulitis after surgical treatment is rare, with the incidence ranging from 1% to 10%. In general, the progression of diverticular disease in the remaining colon is approximately 15%.⁷⁰ In such cases, the previous diagnosis and treatment can be questioned and investigated. Important factors to be considered in terms of surgery are the adequacy of resection, meaning the degree of proximal resection and level of distal anastomosis.^69,71 The use of the rectum as the distal margin decreases the rate of recurrence.

Care also must be taken to exclude other components of differential diagnosis, especially irritable bowel syndrome, inflammatory bowel disease, and ischemic colitis.

Right-Sided Diverticulitis

Diverticulosis in Asia is predominantly a right-sided phenomenon. Diverticula of the right colon may be singular or multiple. The diagnosis of right-sided diverticulitis is difficult to differentiate from appendicitis with a similar clinical picture and presentation. An abdominal mass is usually found in 26% to 88% of cases.^72,73 Surgical treatment is reserved for recurrent and complicated episodes if the diagnosis of right-sided diverticulitis has been made with confidence. If extensive inflammation is present or multiple diverticula are found, a right hemicolectomy with primary anastomosis is indicated. In selected cases, a simple diverticulectomy may be done.⁷⁴

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Practice parameters and guidelines

The practice parameters and guidelines for sigmoid diverticulitis discussed in this chapter are based on guidelines for the treatment of diverticulitis published by the American Society of Colon and Rectal Surgeons (ASCRS) in 2000 and a recent revision, published in 2006.^28,75 Additional pertinent information was retrieved and reviewed from other studies.

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Summary

• The incidence of diverticular disease, particularly diverticulitis, has increased in industrialized countries.
• Diverticular disease can be classified as symptomatic uncomplicated disease, recurrent symptomatic disease, and complicated disease.
• Conservative or medical management is usually indicated for acute uncomplicated diverticulitis. Indications for surgery include recurrent attacks and complications of the disease.
• Surgical treatment options have changed considerably over the years, along with the development of new diagnostic tools and surgical approaches.
• Indications and timing for surgery of diverticular disease are determined mainly by the stage of the disease. In addition, individual patient risk factors, along with the course of the disease after conservative or operative therapy, play a significant role in decision making and treatment.
• In this context, the purpose of this chapter has been to review colonic diverticular disease and its treatment.

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