Colonic diverticula are pouch-like protrusions outward from the colonic wall. They can be single, but more commonly appear as a series of sac-like bulges extending outward from the intestinal lumen. Colonic diverticula can be classified into two types: true and acquired. True diverticula are congenital weaknesses involving all layers of the colonic wall, with the diverticulum containing all layers of the intestinal wall. Acquired diverticula, on the other hand, result from the herniation of the mucosa through weak points in the muscular layer of the intestinal wall. Therefore, they are secondary to increased intraluminal pressure, which forces the mucosa to protrude outward through the weakened areas of the intestinal muscle.

bubble_chart Clinical Manifestations

(1) Colonic Diverticulosis

Approximately 80% of patients with colonic diverticulosis are asymptomatic. If eventually discovered, it is usually an incidental finding during barium enema X-ray or endoscopic examination. Symptoms associated with diverticula are actually manifestations of their complications—acute diverticulitis and bleeding. In uncomplicated colonic diverticulosis, symptoms such as occasional abdominal pain, constipation, and diarrhea are due to accompanying motility disorders, with the presence of diverticula being merely coincidental. Physical examination may reveal grade I tenderness in the left lower abdomen, and sometimes the left colon can be palpated as a firm, tubular structure. Despite abdominal pain, there is no fever or leukocytosis due to the absence of infection. Barium enema imaging may show not only diverticula but also segmental intestinal spasm and muscular thickening, leading to luminal narrowing and a sawtooth appearance.

During an acute episode, patients experience varying degrees of localized abdominal pain, which may be stabbing, dull, or colicky. The pain is mostly located in the left lower abdomen, though occasionally it may be suprapubic, in the right lower abdomen, or throughout the lower abdomen. Patients often report constipation or frequent bowel movements, or sometimes both, with pain relief after passing gas. Inflammation adjacent to the bladder may cause urinary frequency and urgency. Depending on the location and severity of inflammation, nausea and vomiting may also occur. Physical examination findings include low-grade fever, grade I abdominal distension and fullness, tenderness in the left lower abdomen, and a palpable mass in the left lower abdomen or pelvis. Stool tests may reveal occult blood, and in rare cases, gross blood, though massive bleeding is uncommon in the presence of peridiverticulitis. Additionally, mild to grade II leukocytosis may be observed.

Acute diverticulitis is the most common complication of colonic diverticulosis. According to Rodkey and Welch, 43% of colonic diverticulosis cases treated at Massachusetts General Hospital involved acute diverticulitis and localized infection. Acute diverticulitis can occur anywhere in the colon, including the rectum. In Western countries, the sigmoid colon is the most common site, whereas in Japan and China, the right colon is more frequently affected. Among patients known to have diverticulosis, about 10–25% will experience at least one episode of acute diverticulitis. Although massive rectal bleeding is rare during diverticulitis, 30–40% of patients with acute diverticulitis initially present with occult blood in their stool. Approximately 10–25% of patients show no improvement or even deteriorate after 48 hours of treatment, requiring emergency surgery. About 70% of patients undergoing emergency surgery present with severe initial symptoms. Immunocompromised patients respond poorly to medical treatment. Perkins et al. reported that such patients treated with fasting, fluid replacement, and antibiotics had a 100% failure rate, while surgery carried higher morbidity and mortality rates. Therefore, most transplant centers recommend elective colectomy for confirmed diverticulitis before transplantation. Acute diverticulitis is uncommon in patients under 40, and its clinical course is often severe. Freishlay et al. reported that 77% of patients under 40 required surgery during their first episode, often presenting with serious complications such as free perforation. Right-sided colonic diverticula may be part of generalized colonic diverticulosis, an isolated process involving a few diverticula in the right colon, or more commonly, a single true diverticulum. In young patients, right-sided diverticulitis often mimics acute appendicitis.

The most common complication of acute diverticulitis is the formation of an abscess or cellulitis, which may be located in the mesentery, abdominal cavity, pelvis, retroperitoneum, buttock, or scrotum. A tender mass is often palpable during abdominal or pelvic examination, including digital rectal examination. Abscesses caused by diverticulitis are also accompanied by varying degrees of sepsis.

(4) Acute Diverticulitis Complicated by Diffuse Peritonitis

When a confined abscess ruptures or a diverticulum freely perforates into the abdominal cavity, it can cause purulent or fecal peritonitis. Most of these patients present with acute abdomen and varying degrees of septic shock. It is reported that the mortality rate of purulent peritonitis is 6%, while that of fecal peritonitis is as high as 35%.

(5) Acute diverticulitis with fistula formation

Approximately 2% of all patients with acute diverticulitis develop fistulas, but among those who ultimately undergo surgery for diverticular disease, 20% have fistulas. Internal fistulas may arise from adjacent organs adhering to the inflamed colon and adjacent mesentery, with or without the presence of an abscess. As the inflammatory process worsens, the abscess in the diverticulum self-decompresses and ruptures into the adherent hollow organ, thereby forming a fistula. Since the abscess is effectively drained, this outcome often eliminates the need for emergency surgery. About 8% of patients will develop multiple fistulas, with males more likely than females to have multiple fistulas—likely because the uterus in females acts as a barrier separating the sigmoid colon from other hollow organs. Most patients with diverticular colovesical or colovaginal fistulas have previously undergone a hysterectomy. Fistulas caused by diverticulitis can invade many organs, and most colonic cutaneous fistulas—external fistulas—occur in patients who develop anastomotic complications after bowel resection for diverticular disease, specifically anastomotic fistula disease.

Abroad, diverticular disease accounts for about 10% of large intestine obstructions. In domestic cases, complete colonic obstruction caused by diverticular disease is rare, but partial obstruction due to edema, spasm, and inflammatory changes from diverticulitis is common.

bubble_chart Diagnosis

Accurate diagnosis is an extremely important step in determining the condition and deciding the treatment plan. Some patients with mild symptoms and signs of diverticulitis can be successfully treated in outpatient settings, while others presenting with acute life-threatening conditions require emergency resuscitation and life-saving surgery. Therefore, the most crucial assessment involves clinical examination and frequent reevaluation of the patient. This includes not only medical history and physical examination, pulse and temperature, but also serial blood tests, as well as upright and supine abdominal X-rays. When all typical symptoms and signs are present, the diagnosis of left-sided colon diverticulitis is straightforward. In such cases, no additional tests are needed, and treatment should be initiated based on the presumptive diagnosis. Unfortunately, most cases are often unclear, and neither the diagnosis nor the severity of the episode may be evident after the initial clinical examination. In cases of acute right-sided colon diverticulitis, only 7% are correctly diagnosed preoperatively. Preoperative studies are generally unhelpful for diagnosis and may only delay appropriate treatment.

Three tests are useful for confirming the clinical diagnosis of acute left-sided colon diverticulitis and detecting significant inflammatory complications: endoscopy, double-contrast barium enema, and abdominal and pelvic CT scans. In acute cases, endoscopy should generally be avoided because insufflation may induce perforation or exacerbate an existing perforation. If other rectosigmoid pathologies are suspected that could alter treatment, endoscopy may be performed but should avoid insufflation.

Barium enema can be used emergently to diagnose diverticulitis, but there is a risk of barium leakage into the peritoneal cavity, which can cause severe vascular collapse and death. Hackford et al. recommend performing a barium enema 7–10 days after the inflammatory process subsides to confirm the diagnosis. If a more urgent diagnosis is needed to guide treatment, a water-soluble contrast enema can be used, as leakage into the peritoneal cavity would not cause severe reactions.

CT scanning is a non-invasive test that can generally confirm clinically suspected diverticulitis. Enhanced rectal imaging during the scan makes it more sensitive than plain X-rays for detecting diverticular abscesses or fistulas. Labs et al. reported that CT scans are more effective in diagnosing complications of diverticulitis: CT scans identified 10 out of 10 abscesses and 11 out of 12 fistulas, whereas contrast enemas identified only 2 out of 8 abscesses and 3 out of 8 fistulas. Another advantage of CT scans is their ability to guide percutaneous abscess drainage.

Colovesical fistulas due to diverticulitis are best diagnosed by CT scans, which can confirm the diagnosis in over 90% of cases. Cystoscopy may also be necessary, revealing focal inflammatory changes at the fistula site. Barium enema and flexible sigmoidoscopy are less effective, with positive results in only about 30–40% of cases.

Abdominal plain films may reveal colonic obstruction secondary to sigmoid pathology. A water-soluble contrast enema can confirm the diagnosis.

bubble_chart Treatment Measures

(1) Medical Treatment

For uncomplicated acute diverticulitis, medical treatment can be initially adopted, including fasting, gastrointestinal decompression, intravenous fluid replacement, broad-spectrum antibiotics, and close clinical observation. Generally, gastrointestinal decompression is only used when there is vomiting or evidence of colonic obstruction. There are many antibiotics available to control gram-negative aerobic and anaerobic bacilli, and cases of acute diverticulitis resolving spontaneously without antibiotics are also frequently observed. Dietary fiber supplementation and antispasmodics have no role in managing patients with acute diverticulitis. In most cases, symptoms will rapidly improve with medical treatment.

(2) Indications for Surgery

Currently, conditions requiring surgical intervention can be divided into two major categories: one involves uncomplicated diverticular disease, and the other involves various complications caused by diverticulosis. In summary, surgery should be considered for patients with the following conditions: (1) First episode of acute diverticulitis unresponsive to medical treatment; (2) Recurrent acute diverticulitis—even if the first episode responded well to medical treatment, elective resection should be considered upon recurrence; (3) Patients under 50 years old who have had one episode of acute diverticulitis successfully treated medically should undergo elective surgery to avoid emergency surgery later; (4) Immunocompromised patients with diverticulitis cannot mount an adequate inflammatory response, making it a potentially fatal condition, with perforation and rupture into the free peritoneal cavity being very common. Therefore, patients with a history of acute diverticulitis who require long-term immunosuppressive therapy should undergo elective resection beforehand to eliminate the risk of recurrence and complications; (5) Acute diverticulitis complicated by abscess or cellulitis; (6) Acute diverticulitis with diffuse peritonitis; (7) Acute diverticulitis complicated by fistula formation; (8) Acute diverticulitis complicated by colonic obstruction.

Among the above surgical indications, special caution must be taken, particularly in uncomplicated cases, to avoid misdiagnosing patients with irritable bowel syndrome (IBS) and colonic diverticulosis as having diverticulitis and subjecting them to unnecessary surgery. According to Morson, about one-third of specimens from elective surgeries for diverticulitis showed no pathological evidence of inflammation. Therefore, in the absence of objective signs of inflammation such as fever or leukocytosis, IBS with colonic diverticulosis should be managed as a functional colonic disorder and not as a candidate for unnecessary resection.

(3) Surgical Treatment

1. For elective surgery cases, preoperative comprehensive examination and thorough preparation are required, including bowel cleansing and antibiotic prophylaxis. Since the sigmoid colon is the most commonly affected site, it is the primary segment to be resected. The extent of resection is debated, but the appropriate proximal and distal margins must be determined. The colon should be fully mobilized, ensuring good blood supply to the anastomotic segments and tension-free anastomosis. Benn et al. suggest that placing the anastomosis in the rectum significantly reduces the recurrence of diverticulitis. Not all colonic diverticula need to be removed, but no diverticula should remain distal to the anastomosis. The colon previously affected by diverticulitis will show changes on the serosal surface and infiltration in the mesocolon due to prior inflammation, aiding identification. However, even after satisfactory resection, many patients experience enlargement of pre-existing diverticula, progression of diverticulosis, and recurrence of acute diverticulitis in about 7–15% of cases. The recurrence rate of symptoms over time is similar between medically treated and surgically treated patients.

For patients undergoing resection due to unresponsiveness to medical treatment, preoperative bowel preparation may not be feasible. In such cases, Hartmann’s procedure may be chosen, or intraoperative proximal colonic lavage followed by initial-stage (first-stage) end-to-end anastomosis without colostomy may be performed. Recent trends favor initial-stage anastomosis, even after abscess resection, without fecal diversion.

2. During surgery for acute inflammatory complications of diverticulitis, second or third-generation cephalosporins and metronidazole should first be administered intravenously. Some patients may require intravenous stress-dose steroids. The surgeon should anticipate pelvic anatomical factors before the operation, as temporary colostomy or ileostomy may be necessary. This should be explained to the patient and their family preoperatively for mental preparation. Additionally, due to acute inflammatory reactions, the ureters are often involved, increasing the risk of accidental injury during emergency surgery. Therefore, preoperative cystoscopy with ureteral catheter placement for support should be routinely performed.

Emergency surgery patients should be placed in the bladder lithotomy position, and exploration should be performed through a midline abdominal incision. The purpose of the exploration is to confirm the diagnosis, assess the extent of peritoneal inflammation, evaluate the adequacy of bowel preparation, and identify any other lesions. According to Colcock, up to 25% of patients preoperatively diagnosed with diverticulitis accompanied by abscess or fistula are found to have perforated carcinoma during surgery. Clearly, if it is carcinoma, the goals and extent of resection will change. For this reason, Hughes et al. (1963) classified the inflammatory complications of diverticular disease into four categories: (1) localized peritonitis; (2) localized pericolonic or pelvic abscess; (3) diffuse peritonitis following rupture of a pericolonic or pelvic abscess; (4) diffuse peritonitis secondary to free perforation of the colon. Later, Hinchey et al. (1978) proposed a similar classification: (1) pericolonic or mesenteric abscess; (2) walled-off pelvic abscess; (3) diffuse purulent peritonitis; (4) diffuse fecal peritonitis. This classification has been widely adopted. In 1983, Killingback proposed a more complex and refined classification.

For complicated diverticular disease, the best approach is to drain the abscess, control peritonitis, and resect the inflamed intestinal segment. Recent extensive data have shown that conservative drainage and ostomy procedures have significantly higher morbidity and mortality rates compared to resection. The traditional late-stage [third-stage] surgical approach has been replaced by initial-stage [first-stage] and intermediate-stage [second-stage] procedures. Current evidence indicates that initial-stage [first-stage] surgery is safe, but several critical factors must be considered when deciding between initial-stage [first-stage] and intermediate-stage [second-stage] surgery: (1) an empty bowel lumen free of fecal matter, indicating satisfactory bowel preparation or the ability to achieve this through intraoperative irrigation; (2) absence of bowel wall edema; (3) good blood supply to the intended anastomotic segment; (4) localized and not overly severe intra-abdominal infection or contamination; (5) the surgeon's understanding of the patient's overall condition and any other specific risk factors. The recent enthusiasm for initial-stage [first-stage] anastomosis is largely due to the difficulties encountered in restoring bowel continuity in patients who previously underwent Hartmann's procedure for diffuse peritonitis.

As for intermediate-stage [second-stage] surgery, there are two options. The first is the Hartmann procedure, where the distal end is closed, and a proximal colostomy is performed, with anastomosis carried out during the intermediate-stage [second-stage]. This approach is generally suitable for cases of resection due to diffuse purulent peritonitis or diffuse fecal peritonitis. The second option is initial-stage [first-stage] anastomosis with an adjunctive proximal colostomy, ileostomy, or intracolonic bypass. This is typically used for cases not involving diffuse purulent or fecal peritonitis but where other factors preclude initial-stage [first-stage] anastomosis.

There remains disagreement regarding surgery for right-sided colonic diverticulitis. According to Schmit et al., if carcinoma can be ruled out, limited colon resection is sufficient. If carcinoma cannot be excluded or bowel viability is in question, a right hemicolectomy should be performed. However, Fischer and Farkas argue that patients with acute diverticulitis and localized cellulitis can be successfully treated with antibiotics postoperatively, provided carcinoma is excluded and resection is not feasible.