Radiological imaging techniques that are used in the diagnosis of acute diverticulitis are soluble contrast enemas, ultrasound, CT, and magnetic resonance imaging (MRI). Today, soluble contrast enemas are obsolete for diagnosing acute diverticulitis because of their low accuracy and the inability to determine the extent and complications of diverticular disease. The primary disadvantage of contrast enema examination in the evaluation of diverticulitis is that the inflammatory process is predominantly extramucosal. Therefore a contrast enema is often unsuccessful in delineating complications of acute diverticulitis and may underestimate the extent of pericolonic disease. Finally, and perhaps most important, a contrast enema has absolutely no role in the therapeutic intervention for diverticulitis.

Ultrasound is a real-time dynamic examination with wide availability and easy accessibility. Similar to CT, ultrasound is capable of evaluating the transmural involvement of diverticular disease using a ,quick noninvasive technique that eliminates the need for intravenous or intraluminal contrast. In some European countries, ultrasound is routinely used as the initial imaging technique in patients clinically suspected of having acute colonic diverticulitis [36, 37]. However, the use of CT in the evaluation of patients with acute diverticular disease has greatly increased. CT has the advantage of delineating the extent of the extraluminal disease process, provides an unlimited view, and may also direct therapeutic intervention in the case of complicated disease (e.g., CT-guided percutaneous drainage of intra-abdominal abscesses).

The most widely used diagnostic criteria to determine acute diverticulitis with ultrasound and CT are increased thickness of the colonic wall, pericolic fat stranding, and the presence of inflamed diverticula. A high diagnostic sensitivity and specificity are reported for both ultrasound (92 and 90 %, respectively) and CT (94 and 99 %, respectively) [38, 39]. However, abdominal ultrasound is often limited by overlying gas that obscures the diseased segment and may produce false-negative results. This problem is accentuated by obesity and acute diverticulitis, where inflammation may cause a localized ileus in neighboring small-bowel segments. Disease in the distal sigmoid colon is also more difficult to assess because it can be poorly accessible to the ultrasound as a result of interference from the bladder and other pelvic structures. Its main limitation lies in the operator variability inherent in ultrasonography compared with CT, in which subjective interpretation is much less problematic.

MRI has the advantage that no ionizing radiation or intravenous contrast medium is needed to achieve a higher soft-tissue contrast than CT. MRI produces quality images with subtle details superior to those from both CT and ultrasound [40, 41]. MRI does not require the intravenous, oral, and rectal contrast necessary for optimal CT scans. In addition, MRI is not limited by poor visualization caused by overlying gas and fat. However, the high cost and current limited availability of MRI do not make it feasible for routine use at this time. Furthermore, MRI takes significantly longer than CT and may not be acceptable for use in critically ill patients [40, 41].

In conclusion, CT should be the standard radiologic imaging technique for diagnosing acute diverticulitis. CT may be substituted by ultrasound under favorable conditions.

Colonoscopy is not recommended in the acute phase to diagnose acute diverticulitis because of the potential risk of converting a sealed perforation to a free perforation by insufflation of air [42, 43]. Colonoscopy should usually be done 4–6 weeks after an episode of acute diverticulitis in order to exclude a colonic malignancy.

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 intravenous antibiotics. This has been shown to be successful in 70–100 % of patients [46]. 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 follow-up is ensured. If these conditions are not met or the patient fails to improve with outpatient therapy, hospital admission is required. Antibiotics should be selected based on appropriate coverage for gram-negative and anaerobic bacteria [47]. Conservative treatment resolves acute diverticulitis in 85 % of patients [15]. After recovery from the first episode, fiber intake prevents recurrence in more than 70 % of patients [48]. Immunosuppressed or immunocompromised patients are more likely to present with perforation and fail medical treatment [49]. Approximately 15 % of patients develop pericolonic or intramesenteric abscess [50]. 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 a stoma [50].

Surgical treatment of the disease can be emergent or elective, depending on the stage of the disease and the clinical presentation. Intraoperative surgical options are based on the patient’s status and the severity of intra-abdominal contamination [18] (Table 17.1). 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. In advanced stages of peritonitis, the Hartmann procedure (sigmoid colectomy, end colostomy, and closure of the rectal stump) is often performed, but it has been shown that the closure operation (Hartmann reversal) is not only technically challenging but also may be associated with significant postoperative morbidity and mortality [51]. Therefore, in an emergency situation because of free perforation, a primary anastomosis with a defunctioning ileostomy should be favored because the stoma reversal rate after primary anastomosis is higher than after the Hartmann procedure. The Hartmann procedure should be reserved for patients with perforated diverticulitis with severe septic complications. However, the final treatment decision – primary anastomosis or the Hartmann procedure – should depend on the patient’s situation. It is also important that the decision be based not only on intraoperative findings or the extent of peritonitis, but rather on the patient’s overall condition. Anastomotic healing may not occur in an unfit patient, even with mild inflammation, whereas patients with no or few comorbidities may fare well with primary anastomosis despite severe peritonitis [52].

A number of recent publications have discussed the use of laparoscopic peritoneal lavage and drainage for perforated sigmoid diverticulitis, as an alternative to resection [53, 54]. In the case of no localized diverticular bleeding, a subtotal colectomy should be performed if the diverticular bleeding site cannot be localized.

In this context, two prospective randomized studies from the Netherlands and Scandinavia are currently investigating the role of laparoscopic lavage with drainage for purulent and fecal peritonitis (Hinchey III and IV) compared with resection [55, 56]. Pending the results of these studies, laparoscopic lavage with drainage should be critically reviewed and subject to strict indications. According to the available datam the presence of fecal peritonitis or visible perforation is considered a contraindication for this procedure. Classical resection with abdominal lavage should also be performed if immunosuppression or septic disease is present.

The decision for elective colectomy after recovery from acute diverticulitis should be determined individually and with reference to the patient’s characteristics (age, general condition, severity of diverticulitis, and number/frequency of episodes of diverticulitis). In the case of recurrent diverticulitis with complications, such as stenoses or fistulas, surgical treatment is usually necessary.

There are several important points regarding surgical technique. From a technical standpoint, the proximal margin of resection should be in an area of pliable colon without hypertrophy or inflammation. Resection of the diseased colon along with removal of the entire thickened colonic segment is the desired goal. With respect to the extent of resection required, according to current data it is not necessary to remove the entire colonic segment bearing diverticula because such a strategy does not reduce the recurrence rate. The splenic flexure should be mobilized when necessary to perform adequate resection and anastomosis.

When a diverticular phlegmon or abscess extends or ruptures into an adjacent organ, fistulas can arise, the most typical being colovesicular fistulas [60]. The incidence of colovesical fistulas in diverticular disease has been reported to range between 2 and 23 % [61, 62]. Such fistulas have a two-to-one male predominance, attributable to protection of the bladder by the uterus, and a 50 % rate of hysterectomy in female patients with colovesical fistulas. The underlying mechanism is the direct extension of a ruptured diverticulum or erosion of a peridiverticular abscess into the bladder. While sigmoid diverticulitis accounts for the underlying pathology in approximately two-thirds of patients, colovesical fistula has also been reported as a result of cancer of the colon or bladder, radiation therapy, or Crohn’s disease [61, 63]. To date the diagnosis of colovesical fistula due to sigmoid diverticulitis remains a challenge, without a gold standard of treatment. Recurrent or persistent urinary tract infections, urinary frequency, dysuria, and hematuria are the most frequent clinical findings. These symptoms are unspecific, however, and thus diagnosis of colovesical fistula may be delayed. Pneumaturia and fecaluria are considered pathognomonic for colovesical fistulas, but these symptoms are not always present. Diagnostic procedures for colovesical fistulas are conducted to prove the existence of the fistula and to delineate the underlying etiology, as this determines further therapeutic strategy. Diagnostic tests and procedures range from the simple poppy seed test to the chromium nuclear study and the Bourne test to abdominal CT and MRI, cystoscopy, and colonoscopy [64–66]. Different from advanced cancer resection for colovesical fistula because of sigmoid diverticulitis, sigmoid segment resection and closure of the bladder defect is required for colovescial fistulas. In view of a spontaneous closure rate of only 2 % for colovesical fistulas [67, 68], and inflammatory complications in up to three-quarters of patients [69, 70], the existence of colovesical fistulas should be seen as an indication for surgery. Conservative or endoscopic procedures remain reserved for individual cases.