Colonic diverticulosis is among the most common diseases of developed Western countries. An increase in its prevalence has been documented, and a low-fiber diet has been shown to be the major etiologic factor among other predisposing factors.^1,2 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 age 85^3,4 and it also affects a significant proportion of younger adults. Diverticulosis is often asymptomatic; however, 10% to 25% of patients with diverticulosis will ultimately progress to diverticulitis and present with symptoms ranging from minor complaints to life-threatening sequelae.^5,6 Patients with acute complications may require hospital admission and treatment varying according to the stage of disease.

In this educational article, we summarize colonic diverticular disease, its pathogenesis and treatment in accordance with the literature and guidelines prepared and recommended by the Standard Task Force of the American of Colon and Rectal Surgeons,⁷ and the ad Hoc Practice Parameters Committee of the American College of Gastroenterology.^3,8,9

The true prevalence of diverticulosis is difficult to measure since most individuals are asymptomatic. A comparison of the earliest and most recent autopsy and barium enema studies indicate that the prevalence is increasing over time throughout the world.^7,10,11 Other than this, studies so far include barium examinations and necropsy series that may be misleading for determining the actual prevalence rate, 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.^12,13 Whether these results are due to increased numbers of older individuals in the population, increased screening, or a true rise in prevalence is not known.

Diverticulosis is most prevalent in industrialized countries, where studies have confirmed the findings of diverticula in about 5 to 10% of the population by age 50, 30% of those aged over 50, in 50% of those over 70 and in 66% of people over 85 years of age. (Table 1)¹⁴

Younger patients presenting below the age of 40 have a prevalence rate of 5% and are more commonly male.^15,17 Symptomatic and complicated disease affects only a small proportion of those individuals with anatomic diverticulosis coli. There are also some predisposing factors such as obesity, decreased physical activity, corticosteroids, alcohol and caffeine intake, cigarette smoking, and renal failure resulting from polycystic kidney disease.^8,18,19 Studies have shown that genetic as well as environmental factors play a role in the pathogenesis of the disease.

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.^20,21 These vessels enter the colonic wall on either side of the mesenteric taenia and on the mesenteric border of the two antimesenteric taeniae. Diverticula do not develop in the rectum, presumably because of the coalescence of the taenia with the longitudinal muscle layer that marks the junction between the sigmoid colon and the rectum. Mychosis, a set of findings consisting of the thickening of the muscular layer, shortening of the taeniae, and luminal narrowing, is to be found in most patients with sigmoid diverticula.
The mechanical features of the colonic wall change with increasing age.^22,23 Combined barostat-manometry studies of the entire colon demonstrated that compliance is lowest in the sigmoid and descending colon and greatest in the transverse and ascending colon.²³ This difference in mechanical properties between the right and left sides might partly account for the left-sided predominance of diverticulosis.²⁴

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 the integrity of the colonic wall.^25,26 Changes in the quality and quantity of 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.²⁷ These changes may be either related to a genetic predisposition such as seen in Ehlers-Danlos and Marfan's syndromes, which may be responsible for occurrence of diverticula at an early age, or to the natural course of aging process itself.

In a study, it was reported that collagen fibrils in the left colon were smaller and more tightly packed than those in the right colon with increasing age, and that this difference was accentuated in diverticular disease.²⁶

The thickening of longitudinal and circular muscles in diverticular disease is neither hyperplasia nor hypertrophy, but appears to be related to a contractile state. An increase in the number of elastic fibers was observed only in the longitudinal muscle.²⁸ It was suggested that this process was responsible for longitudinal contraction with subsequent thickening of both muscle layers.²⁸ All these changes, along with elastin deposition in teniae coli, lead to an irreversible state of contracture with substantial bowel shortening that may result in decreased resistance of the colon wall to persistent intraluminal pressure.²⁹

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. But segmentation on its own separates the colonic lumen into a series of chambers, each having a different amount of pressure closely related to the chamber's diameter. These isolated increases of intraluminal pressure are thought 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 within the colon leading to bulkier and more voluminous stools. Thereby fiber decreases the frequency of contractions and prevents exaggerated form of segmentation.^13,30,31 In addition, dietary fiber influences the content of colonic bacterial flora, forms the main substrate for the bacterial carbohydrate fermentation and produces energy-yielding substrates, i.e. the short-chain fatty acids, for growth and maintenance of colonic cellular function. Therefore, 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.^13,32

After development of colonic diverticula, either a spectrum of inflammatory changes or bleeding due to the traumatic injury to penetrating vessels may take place.^20,21 Changes 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 range from localized subclinical inflammation to generalized peritonitis with free perforation. (Figure 2) This, in turn, leads to hyperplasia of the lymphoid tissue within the mucosa at the base of the diverticulum, which is one of the earliest signs of diverticulitis.

Inflammation usually begins at the apex of the diverticulum and seldom involves the neck or the 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, which can spread circumferentially and longitudinally and may be responsible for the pathologic picture of diverticular colitis. Especially, longitudinal tracking may result in fissuring along with the lymphoid aggregates, which resembles the distinctive feature of colonic colitis in Crohn's disease.³³ This may cause misinterpretation of the pathological study of the specimen. Therefore, the differential diagnosis of these two conditions in terms of pathological 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 present 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 that is indistinguishable from a neoplasm macroscopically. Another pathological entity that may be encountered along the progression of the disease with the recurrent attacks of diverticulitis is the formation of a localized abscess with chronic inflammation and involvement of other neighboring luminal organs such as bladder, small and large bowel loops, uterus and vagina. Fistulae within this containment between involved segment(s) of colon and these organs may develop. Fistulae occur in 2.4% to 20% of cases; 65% of these fistulae are colovesical and 20% are colovaginal fistulae.^34-36

Most people with uncomplicated colonic diverticulosis are asymptomatic. A small proportion of these patients may have troublesome symptoms such as colicky abdominal pain, bloating, flatulence, or altered bowel habit. Their 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), since these two clinical entities are mostly diagnosed after other pathologies are excluded. IBS-type symptoms are independent of the presence or absence of diverticulosis on double-contrast barium enema. Bleeding alone can sometimes be the one and only sign of diverticulosis.³⁷

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 (Table 2). Patients with acute uncomplicated diverticulitis classically present with left-sided lower abdominal pain, fever, and leukocytosis.⁷ 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 disturbance with alteration of bowel habits: constipation, either alone or alternating with bouts of diarrhea; anorexia; or nausea and vomiting. Urinary symptoms such as dysuria, frequency, and urgency may develop in a minority of patients, probably caused by 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 due to perforation and spreading of inflammation in the peritoneum. The 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.

Initial assessment of patients with suspected acute diverticulitis comprises a thorough history and physical examination including abdominal, rectal, and pelvic examinations. Useful initial examinations may include complete blood cell count, urinalysis, and flat and upright abdominal radiographs. If the clinical picture is clear enough to diagnose diverticulitis, no other tests are indicated.³ When the diagnosis is in question, other tests such as CT, water-soluble contrast enema, and ultrasound may be performed. One should also consider the differential diagnosis of acute diverticulitis, including colon cancer, appendicitis and cholecystitis, inflammatory bowel disease, IBS, ischemic colitis, and gynecologic and urologic diseases,³⁸ not only during examination of the patient but also while ordering the tests (Table 3). Especially, the differential diagnosis of colorectal cancer as well as the detection of its possible coexistence is very important.^39,40 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 the mortality related to barium-induced chemical peritonitis.⁴⁰ 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.^41,42 It is helpful, especially in female patients, for excluding pelvic and gynecologic pathology . CT, with a sensitivity of 69% to 95% and a specificity of 75% to 100%, is generally superior to contrast studies.^39,43-46 CT with triple contrast—eg, oral, rectal, and IV contrast—has become increasingly used as the initial imaging study especially in the acute setting, particularly whenever moderately severe disease or abscess is anticipated. It is also 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. CT is not useful in differentiating cancer from diverticulitis and must be supplemented by contrast enema or endoscopy. Although endoscopy is rarely indicated in an acute setting, if required it should be done with very gentle and cautious insufflation and manipulation because of the risk of perforation of acutely inflamed colon either by insufflation of air or by the instrument itself. It can be performed with better safety after the patient recovers from the acute attack.

Uncomplicated acute diverticulitis refers to cases with clinical signs and symptoms of acute diverticulitis without associated abscess, fistula, obstruction, or free perforation. In the absence of systemic signs and symptoms, patients with mild abdominal tenderness may be treated conservatively on an outpatient basis. Treatment involves broad-spectrum antibiotics for 7 to 10 days (Table 4) along with a low-residue diet.^7,9 However, patients with increasing abdominal tenderness, fever, or inability to tolerate an oral diet need to be hospitalized. Treatment of this group usually involves bowel rest along with IV fluids and broad-spectrum antibiotics covering mainly gram-negative rods and anaerobes. For analgesia, meperidine is preferred over morphine since morphine may increase intracolonic pressure in the sigmoid colon. The initiation of medical therapy usually results in rapid clinical improvement with resolution of pain, fever, and ileus within 48 to 72 hours. Antibiotics are again continued for 7 to 10 days, and oral feedings initially as residual diet are gradually reintroduced. Patients who recover from an attack should be placed on a high-fiber diet to decrease the likelihood of repeated attacks.

After discharge, patients need further evaluation with either a combination of flexible sigmoidoscopy and contrast enema or with colonoscopy.⁴⁷ Patients meeting the criteria for elective or semielective surgery include (1) those who have had two or more acute attacks successfully treated medically; (2) patients with one attack that included either contained perforation, colonic obstruction, or inflammatory involvement of neighboring organs such as the bladder with a fistula; or (3) patients with suspicious colonic carcinoma that cannot be excluded. Finally, although still controversial as a treatment option in younger patient populations, (4) patients less than 50 years old with a single attack requiring hospitalization may be treated surgically because this patient group has longer a life expectancy, which increases the possibility and the risk of subsequent episodes and related complications.⁴⁸ In general, patients receiving steroid or immunosuppressant therapy should not be treated on an outpatient basis. Semielective surgery should be performed during the same hospitalization.

Surgical treatment options are covered in Part 2 of this chapter.

More acute advanced disease can be treated surgically on an emergent basis where surgical options may vary according to the preoperative factors, the patient's condition, and intraoperative staging of peritonitis. These all contribute to the peritonitis scoring system (Table 5). There are many different staging systems that depend on the stage of presentation of intra-abdominal pathology for evaluating and treating. Among these systems, the Hinchey classification,^7,49 recommended in the guidelines for treatment of diverticular disease by the American Society of Colon and Rectal Surgeons (http://www.fascrs.org/
displaycommon.cfm?an=1&subarticlenbr=150) and the American Gastroenterological Association, is the most commonly used tool for making the surgical decision based on intraoperative findings (Table 6). Surgical treatment options, with the contribution of auxiliary methods like CT-guided drainage and on-table lavage to downstage the type and complexity of the surgical operations, may be based on the Hinchey classification.^7,50

The most commonly performed procedures are either single-stage or two-stage procedures that can be performed either laparoscopically (in experienced hands) or by the conventional open method, depending on the severity and stage of disease, the patient's overall condition, and comorbidities. Primary resection and anastomosis without a protective stoma is the so-called single-stage procedure that is usually the treatment of choice for patients without immunosuppression or immunocompromised status presenting with either uncomplicated diverticulitis or a clinical picture that could be downstaged by means of the above-mentioned methods (Figure 3). A two-stage procedure is commonly indicated for patients with substantial fecal contamination, inflammation, and immunocompromised or immunosuppressed status. The two-stage procedure consists of either initial resection of the diseased segment and elective restoration of the intestinal continuity later on (Hartmann's procedure) or resection and primary anastomosis with a proximal loop ileostomy that again is to be closed at a later appropriate time (Figure 4). The most commonly performed two-stage operation is Hartmann's procedure, which has great variability of morbidity and mortality related to the selection and application criteria to different patient populations (Figure 5). Mortality ranges from 2.6% to 36.8%.^51-56

To summarize, the surgical treatment options and their stage-related clinical applications are as follows.^7,9,57 Hinchey stage 1 disease (Figure 6) is initially treated conservatively using IV antibiotics for the first 48 hours. If the clinical condition of the patient fails to improve within this period, a repeat CT is usually indicated. An increase in abscess size on CT renders CT-guided drainage the next available treatment option in the treatment algorithm. Patients with abscesses that are not amenable to CT-guided drainage or in whom signs and symptoms of peritonitis persist despite appropriate antibiotic therapy and percutaneous drainage are candidates for surgical intervention. In stage 2, diverticulitis is associated with distant abscesses (retroperitoneal or pelvic) (Figure 7). Magnitude, location, patient's clinical factors determining timing of surgery and treatment modality. Again, small abscesses may resolve with antibiotic therapy and bowel rest. Large diverticular abscesses can be either percutaneously or surgically drained. Percutaneous drainage may allow stabilization of the patient and avoidance of a temporary stoma and a second operation. Abscesses that are not amenable to CT-guided percutaneous drainage and those that are resistant to conservative therapy in terms of clinical improvement require surgical treatment. In extraordinary conditions, as in an immunocompromised or toxic patient or in a patient with marked pelvic inflammatory residue after resection of a diseased colonic segment, a proximal loop ileostomy might be indicated (Figure 4) The occasional patient can undergo primary resection and anastomosis. Stage 3 disease (Figure 8) is a state of purulent peritonitis, which is a surgical emergency requiring preliminary optimization and immediate resuscitation with IV fluids, broad-spectrum antibiotics, cardiovascular support when indicated, and prompt surgical therapy. Depending on the degree of contamination, magnitude of sepsis, and timeliness of surgical intervention, a 6% to 35% mortality rate can be expected. The Hartmann procedure is still the main surgical option according to the literature (Figure 5); however, resection and anastomosis with loop ileostomy may still be an option in selected cases. Several retrospective analyses suggest that primary resection and anastomosis is preferable.^58-61 It is difficult to assess the relative safety of primary resection and anastomosis with or without loop ileostomy versus a Hartmann procedure. On the other hand, one must also consider the 30% possibility that Hartmann's procedure is irreversible and the additional morbidities that might be encountered related to this procedure. In patients with a score of IV/V on the scale of the American Society of Anesthesiologists, preoperative organ failure is best managed without an anastomosis. ASA score along with the other criteria mentioned in the peritonitis severity score (Table 5) are useful in decision making and treatment of these patients.⁵⁷

Again, patients with an immunocompromised status, those more than 70 years old, and those with signs and symptoms of systemic toxicity should have a diversion (Figure 4). In stage 4 disease, which is fecal peritonitis (Figure 9), patients require surgical intervention after preliminary optimization and resuscitation. Almost all patients should be treated with Hartmann's procedure and drainage. In rare prohibitive cases with adhesions and conditions that hinder effective segmental resection, peritoneal lavage, proximal fecal diversion, omentoplasty, and possible drainage may be considered (Figure 10).

The outcomes of stage-related surgical treatment modalities have been reviewed and reported in the literature. In a retrospective study, 53 (87%) patients were treated with resection and non-diverted coloproctostomy for stage I disease. In this group, only 2 (3.8%) anastomotic leaks occurred, and the observed overall morbidity rate was only 22%. In stage II disease, 27(69%) underwent primary resection with coloproctostomy. Eleven patients out of 27 had proximal diversion whereas 16 had none. The overall leak rate was identical at 3.8%, but the group's morbidity rate of 30% was slightly increased.⁶²

According to the literature, laparoscopic treatment of diverticulitis especially in Hinchey I and II disease can be performed without additional morbidity and mortality. In a comperative study, patients with Hinchey II disease had no statistical difference between complication rates for laparoscopic surgery versus conventional laparotomy.^63,64

In Stage III and IV disease, mortality rates of surgical treatment options such as diversion and suture closure, Hartmann's procedure (resection and end colostomy), primary resection and anastomosis, and finally resection with proximal diversion were reviewed and reported as 26%, 12%, 9% and 6% for each individual operation type respectively.⁵⁸ The outcomes as given favor resection with coloproctostomy over Hartmann's procedure. However, in most of these studies they considered using primary resection with coloproctostomy only in selected patients without any randomization. Therefore, in stage III and IV disease this still needs to be tested by means of prospective randomized trials before making any recommendation regarding its therapeutic application.

Laparoscopic surgery for acute complicated disease in association with Hinchey III and IV has not been generally accepted as the treatment of choice. However, evidence shows that laparoscopy has been used as a diagnostic tool along with the laparoscopy assisted- lavage procudere in Hinchey III patients.⁶⁵

In summary, diverticulitis is a commonly encountered clinical entity in daily practice and needs to be taken into consideration especially in the differential diagnosis of patients with abdominal complaints. The increase in morbidity and mortality is determined to be associated with the stage of the disease. It is worthwhile to emphasize that it requires a multidisciplinary approach for its staging, diagnosis and treatment.

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