August 2004

Section 5 Gastrointestinal Tract and Abdomen

Figure 1. Colon segment containing diverticula

Diverticula are small (0.5 to 1.0 cm in diameter) outpouchings of the colon that occur in rows at sites of vascular penetration between the single mesenteric taenia and one of the antimesenteric taeniae. At the sites of most diverticula, the muscular layer is absent [see Figure 1]. Technically, such lesions are really pseudodiverticula; true diverticula (which are much less common than pseudodiverticula) involve all layers of the bowel wall. Nevertheless, both pseudodiverticula and true diverticula are generally referred to as diverticula.

The sigmoid colon is the most common site of diverticula: in 90% of patients with diverticulosis, the sigmoid colon is involved.¹ If a diverticulum becomes inflamed as a result of obstruction by feces or hardened mucus or of mucosal erosion, a localized perforation (microperforation) may occur—a process known as diverticulitis. The incidence of diverticulitis is about 10% to 25% in patients with colonic diverticula.¹ Both diverticulosis and variants of diverticulitis may be subsumed under the more encompassing term diverticular disease.

The incidence of diverticular disease increases with age. Diverticula are quite common in elderly patients, being present in more than 80% of patients older than 85 years.² Consequently, as the population of the United States continues to age, the overall risk of diverticular complications continues to increase.³ Before the 20th century, diverticular disease was rare in the United States. By 1996, however, 131,000 patients were being admitted to hospitals with diverticulitis each year.⁴

Figure 2. Schematic representation: segmentation in the colon

A diet containing refined carbohydrates and low-fiber substances, such as is currently widespread in many developed countries (especially in the West), has been associated with the emergence of this disease entity.^5,6 A low-residue diet facilitates the development of constipation, which can lead to increased intraluminal pressure in the large bowel. In addition, elevated elastin levels are commonly noted at colon wall sites containing diverticula,⁷ and this change causes shortening of the taeniae.¹ High-pressure zones or areas of segmentation may develop [see Figure 2], usually in the sigmoid colon, and diverticula begin to protrude at these locations. If microperforation of a thin-walled diverticulum takes place, local or, sometimes, widespread contamination with fecal organisms may ensue. The pericolonic tissue (typically, the mesentery and the pericolic fat) thus becomes inflamed while the mucosa tends to remain otherwise normal.

Several factors appear to promote the development of diverticular disease and its complications, including decreased physical activity,⁸ intake of nonsteroidal anti-inflammatory drugs (NSAIDs),^9,10 smoking,¹¹ and constipation from any cause (e.g., diet or medications). The well-known Western afflictions cholelithiasis, diverticulosis, and hiatal hernia frequently occur together (Saint's triad). Obesity has been associated with the intake of low-fiber diets,¹² and growing numbers of young, obese patients with diverticulitis are being seen by physicians.

History

Uncomplicated (Simple) Diverticulitis

The classic symptoms of uncomplicated acute diverticulitis are left lower quadrant abdominal pain, a low-grade fever, irregular bowel habits, and, possibly, urinary symptoms if the affected colon is adjacent to the bladder. If the sigmoid colon is highly redundant, pain may be greatest in the right lower quadrant. Diarrhea or constipation may occur, together with rectal urgency.

Figure 3. Napkin-ring carcinoma

The differential diagnosis includes gynecologic and urinary disorders, perforated colon carcinoma, Crohn disease, ischemic colitis, and, sometimes, appendicitis. Chronic diarrhea, multiple areas of colon involvement, perianal disease, perineal or cutaneous fistulas, or extraintestinal signs are suggestive of Crohn disease. Rectal bleeding should raise the possibility of inflammatory bowel disease, ischemia, or carcinoma; such bleeding is uncommon with diverticulitis alone. Given the prevalence of diverticula, it is not surprising that colon carcinoma may coexist with diverticular disease [see Figure 3].

Complicated Diverticulitis

Figure 4. Major complications of diverticular disease

Some cases of diverticulitis are classified as complicated, meaning that the disease process has progressed to obstruction, abscess or fistula formation, or free perforation [see Figure 4]. Complicated diverticulitis may be particularly challenging to manage,^13,14 especially because patients may have no known history of diverticular disease.¹⁵ Lower gastrointestinal bleeding is also a complication of diverticular disease in 30% to 50% of cases¹⁶; in fact, diverticula are the most common colonic cause of lower GI bleeding.¹⁶ When diverticular hemorrhage occurs [see 5:6 Lower Gastrointestinal Bleeding ], it is usually associated with diverticulosis rather than with diverticulitis. Approximately 50% of diverticular bleeding originates in the right colon, despite the low incidence of diverticula in this segment of the colon. Patients tend to be elderly¹³ and to have cardiovascular disease and hypertension. Regular intake of NSAIDs may increase the risk of this complication. Although patients may lose 1 to 2 units of blood, the bleeding usually ceases spontaneously,¹⁷ and expeditious operative treatment generally is not necessary.

Figure 5. Hinchey classification

The most common form of complicated diverticulitis involves the development of a pericolic abscess, typically signaled by high fever, chills, and lassitude. Such abscesses may be small and localized or may extend to more distant sites (e.g., the pelvis). They may be categorized according to the Hinchey classification of diverticular perforations,¹⁸ in which stage I refers to a localized pericolic abscess and stage II to a larger mesenteric abscess spreading toward the pelvis [see Figure 5]. On rare occasions, an abscess forms in the retroperitoneal tissues, subsequently extending to distant sites such as the thigh or the flank. The location of the abscess can be defined precisely by means of computed tomography with contrast.

Some abscesses rupture into adjacent tissues or viscera, resulting in the formation of fistulas. The fistulas most commonly seen in this setting (50% to 65% of cases) are colovesical fistulas. This complication is less common in women because of the protection afforded by the uterus. Symptoms of colovesical fistulas tend to involve the urinary tract (e.g., pneumaturia, hematuria, and urinary frequency). Fecaluria is diagnostic of colovesical or enterovesical fistulas. Colovaginal fistulas (which account for 25% of all diverticular fistulas) are usually seen in women who have undergone hysterectomies.¹⁹ The diseased colon is adherent to the vaginal cuff. Most commonly, patients complain of a foul vaginal discharge; however, some patients present with stool emanating from the vagina.

About 10% of colon obstructions are attributable to diverticulitis. Acute diverticulitis can cause colonic edema and a functional obstruction that usually resolves with antibiotic infusion and bowel rest. Stricture formation is more common, usually occurring as a consequence of recurrent attacks of diverticulitis. Circumferential pericolic fibrosis is noted, and marked angulation of the pelvic colon with adherence to the pelvic sidewall may be seen. Patients complain of constipation and narrowed stools. Colonoscopy can be difficult and potentially dangerous in this setting. Differentiating a diverticular stricture from carcinoma may be impossible by any means short of resection.

The term malignant diverticulitis has been employed to describe an extreme form of sigmoid diverticulitis that is characterized by an extensive phlegmon and inflammatory reaction extending below the peritoneal reflection, with a tendency toward obstruction and fistula formation.²⁰ Malignant diverticulitis is seen in fewer than 5% of patients older than 50 years who are operated on for diverticulitis.²⁰ The process is reminiscent of Crohn disease, and CT scans demonstrate extensive inflammation. In this setting, a staged resection might be preferable to attempting a primary resection through the pelvic phlegmon. The degree of pelvic inflammation may subside significantly after diversion.²⁰

A dangerous but rare complication of acute diverticulitis (occurring in 1% to 2% of cases) is free perforation,²¹ a term that includes both perforation of a diverticular abscess throughout the abdomen leading to generalized peritonitis (purulent peritonitis; Hinchey stage III) and free spillage of stool thorough an open diverticulum into the peritoneal cavity (fecal peritonitis; Hinchey stage IV). The incidence of free perforations may be increasing, at least in the southwestern United States.²² The overall mortality in this group is between 20% and 30%; that for purulent peritonitis is approximately 13%, and that for fecal peritonitis is about 43%.²¹

Imaging

Figure 6. CT: acute diverticulitis

Figure 7. CT: thickened colonic wall and diverticulum

The most useful diagnostic imaging study in the setting of suspected diverticulitis is a CT scan with oral and rectal contrast.²³ Localized thickening of the bowel wall or inflammation of the adjacent pericolic fat is suggestive of diverticulitis; extraluminal air or fluid collections are sometimes seen together with diverticula [see Figure 6]. The most frequent findings (seen in 70% to 100% of cases) are bowel wall thickening, fat stranding, and diverticula.²⁴ In some cases, small abscesses in the mesocolon or bowel wall are not detected. The diagnosis of carcinoma cannot be excluded definitively when there is thickening of the bowel wall [see Figure 7].²

Figure 8. Local extravasion from sigmoid colon

Figure 9. Extravasation into abscess cavity

Although CT scanning has tended to replace contrast studies in the evaluation of diverticulitis, the latter may be more useful in differentiating carcinoma from diverticulitis. A contrast study can also be complementary when the CT scan raises the suspicion of carcinoma.²³ When diverticulitis is suspected, water-soluble contrast material should be used instead of barium because of the complications that follow extravasation of barium [see Figures 8 and 9]. Furthermore, in the acute setting, only the left colon should be evaluated. Carcinoma is suggested by an abrupt transition to an abnormal mucosa over a relatively short segment; diverticulitis is usually characterized by a gradual transition into diseased colon over a longer segment, with the mucosa remaining intact. If the contrast study reveals extravasation of contrast outlining an abscess cavity [see Figure 9], an intramural sinus tract, or a fistula, diverticulitis is likely.¹

Figure 10. Colonoscopic view of sigmoid diverticula

Colonoscopy is avoided when acute diverticulitis is suspected, because of the risk of perforation. It may, however, be done 6 to 8 weeks after the process subsides to rule out other disorders (e.g., colon cancer) [see Figure 10]. If diverticular disease is advanced, the endoscopic procedure may be difficult; the diverticular segment must be fully traversed for the examiner to be able to exclude a neoplasm with confidence. When major lower GI bleeding occurs, colonoscopy is done to search for polyps, carcinoma, or a site of diverticular bleeding. In the case of massive bleeding, selective arteriography is useful for localizing the source, and superselective embolization frequently quells the hemorrhage. The actual risk of bowel ischemia is low when superselective techniques are employed. Bleeding at the time of arteriography may be facilitated by the infusion of heparin or urokinase; however, this is a risky approach that should be taken only when other attempts at localization have failed and recurrent bouts of bleeding have occurred.

Figure 11. CT: colovesical fistula

When a colovesical fistula occurs, contrast CT with narrow cuts in the pelvis can be very helpful. The classic findings are sigmoid diverticula, thickening of the bladder and the colon, air in the bladder, opacification of the fistula tract and the bladder, and, possibly, an abscess [see Figure 11]. Cystoscopy is less specific, showing possible edema or erythema at the site of the fistula. A contrast enema helps rule out malignant disease. The diagnostic tests that are most useful for detecting colovaginal fistulas are contrast CT and vaginography via a Foley catheter. Charcoal ingestion helps confirm the presence of colovesical or colovaginal fistulas. On rare occasions, colocutaneous fistulas may develop, causing erythema and breakdown of the skin. Colouterine fistulas may occur as well; these are also quite rare.²⁵

Uncomplicated diverticulitis is usually managed on an outpatient basis by instituting a liquid or low-residue diet and administering an oral antibiotic combination that covers anaerobes and gram-negative organisms (e.g., ciprofloxacin with metronidazole or clindamycin) over a period of 7 to 10 days. Provided that symptoms and signs have subsided, the colon may be evaluated more fully several weeks later with a contrast study or colonoscopy if the diagnosis of diverticular disease has not already been established. If symptoms worsen, hospitalization should be considered. Over the long term, patients should be maintained on a high-fiber diet, though it may take months for the diet to have an effect on symptoms.²⁶

Figure 12. Treatment options for complicated diverticulitis

If more significant physical findings and symptoms of toxicity develop, hospitalization is warranted [see Figure 12]. Patients are placed on a nihil per os (NPO) regimen, and intravenous fluids and antibiotics are administered (e.g., a third-generation cephalosporin with metronidazole) until abdominal pain and tenderness have resolved and bowel function has returned. As a rule, resolution occurs within several days. If there is clinical evidence of intestinal obstruction or ileus, a nasogastric tube is placed. In most cases, ileus-related symptoms resolve with antibiotic treatment. CT scans are useful for establishing the correct diagnosis in the emergency department²⁷; furthermore, the severity of diverticulitis on CT scans predicts the risk of subsequent medical failure.²⁸ Following the sedimentation rate may be helpful in assessing the effectiveness of treatment. It has been estimated that 15% to 30% of patients admitted with acute diverticulitis will require surgical treatment during the same admission.¹

Figure 13. CT scan: pericolonic abscess

If fever and leukocytosis persist despite antibiotic therapy, the presence of an abscess should be suspected. Small (< 5 cm) abscesses may respond to antibiotics and bowel rest. Larger abscesses that are localized and isolated may be accessible to percutaneous drainage [see Figure 13].²⁸ Generally, this technique is reserved for abscesses greater than 5 cm in diameter in low-risk patients who are not immunocompromised. It often leads to resolution of sepsis and the resulting symptoms and signs (e.g., abdominal pain and tenderness and leukocytosis), usually within 72 hours, thereby facilitating subsequent elective surgical resection of the colon. In addition, percutaneous drainage offers cost advantages, in that it reduces the number of operative procedures required and shortens hospital stay.

Access to a pelvic collection may be difficult to obtain, and the drainage procedure typically must be done with the patient in a prone or lateral position. If the catheter drainage amounts to more than 500 ml/day after the first 24 hours, a fistula should be suspected. Before the catheter is removed, a CT scan is done with injection of contrast material through the tube to determine whether the cavity has collapsed. If this approach fails (as it usually does in patients with multiple or multiloculated abscesses), an expeditious operation may be necessary.²² An initial surgical procedure is required in about 20% of cases.²⁹

Overall, approximately 20% of patients with diverticulitis require surgical treatment.^2,30 Most surgical procedures are reserved for patients who experience recurrent episodes of acute diverticulitis that necessitate treatment (inpatient or outpatient) or who have complicated diverticulitis. The most common indication for elective resection is recurrent attacks—that is, several episodes of acute diverticulitis documented by studies such as CT. Estimates of the risk of such attacks range from 30% to 45%. A task force of the American Society of Colon and Rectal Surgeons recommended sigmoid resection after two attacks of diverticulitis.³¹ A cost analysis using a Markov model suggested that cost savings can be achieved if resection is done after three attacks.³² Efforts are made to time surgical treatment so that it takes place during a quiescent period 8 to 10 weeks after the last attack. Barium enema or colonoscopy may be employed to evaluate the diverticular disease and rule out carcinoma. The bowel can then be prepared mechanically and with antibiotics (e.g., oral neomycin and metronidazole on the day before operation).

Elective resection is a common sequel to successful percutaneous drainage of a pericolic abscess in an otherwise healthy, well-nourished patient. The timing of surgery may be guided by the extent of the inflammatory changes (as documented by CT scanning) and the patient's clinical course. Most patients can be operated upon within 6 weeks. Elective resection is the preferred approach to diverticular fistulas as well. Colovesical fistulas are usually resected because of the risk of urinary sepsis and the concern that a malignancy might be overlooked. Preferably, the operation is done when the acute inflammation has subsided.

Elective resection is done via either the open route or, increasingly, the laparoscopic route³³; a few telerobotic-assisted laparoscopic colectomies have also been attempted.³⁴ The learning curve for laparoscopic colectomy is 20 to 50 cases.³⁵ Obese patients with severe colonic inflammation are poorer candidates for laparoscopic resection.³³ In our institution, the development of hand-assisted procedures has widened the opportunities for utilizing minimally invasive surgery [see 5:32 Procedures for Diverticular Disease].^40,41

Some patients with complicated diverticulitis require emergency resection because of free perforation and widespread peritonitis. In such patients, the American Society of Anesthesiologists (ASA) physical status score and the degree of preoperative organ failure may be significant predictors of outcome.^42,43 Unfavorable systemic factors (e.g., hypotension, renal failure, diabetes, malnutrition, immune compromise, and ascites) play a vital role in determining patient outcome,⁴³ as does the severity of the peritonitis (i.e., extent, contents, and speed of development).^44,45 One of the unfortunate limitations of the Hinchey classification is that it does not take comorbidities into account.⁴⁴ Because the bowel is not prepared before operation, the surgeon may feel uncomfortable doing an anastomosis. On-table lavage may be considered if contamination is minimal, but it adds to the time spent under anesthesia during an emergency procedure.

As a general rule, resection and immediate anastomosis are suitable for Hinchey stage I and perhaps stage II diverticular perforations, whereas resection with diversion (the Hartmann procedure) is the gold standard for stage III and especially stage IV.^46–48 This recommendation is based on the finding that an anastomosis involving the left colon is risky when performed under emergency conditions.⁴⁹ The once-popular three-stage procedures are now of historic interest only. There are some reports of successful outcomes for type III and type IV cases after extensive abdominal lavage and two-layer anastomoses⁵⁰ or after on-table lavage of the colonic contents to allow primary anastomosis.⁵¹ Grading of comorbidities with classification systems such as APACHE II or the Mannheim peritonitis index can facilitate decision-making with respect to the question of anastomosis versus diversion.⁵² The surgeon's decision must be individualized on the basis of each patient's condition and needs. The literature on this topic is confusing, in that most of the published reports are small and retrospective, with only limited classification of disease severity.

Currently, surgeons encountering acute diverticulitis are more likely to do one-stage resections, as opposed to Hartmann procedures, than they once were.^43,53 The advantage of the one-stage approach is that the colostomy takedown and the attendant 4% mortality are avoided.⁵⁴ Furthermore, at least 30% of patients who undergo a Hartmann procedure never return for colostomy closure. A primary anastomosis can be protected with a proximal ileostomy as well.^46,55,56 Transverse colostomy and loop ileostomy appear to be equally safe, though skin changes may be more problematic after a colostomy⁵⁷ and an ileostomy closure tends to be less complex than a colostomy closure. On-table lavage may also be used as an adjunct to anastomosis.⁵⁸

The risk of complications inherent in operations on the colon should always be kept in mind, especially in the relatively few patients undergoing emergency procedures. In this setting, the bowel is unprepared and systemic sepsis may be present. Potential complications include ureteral injuries; anastomotic leakage, anastomotic stricture, and postoperative intra-abdominal abscesses; perioperative bleeding involving the mesentery, adhesions, the splenic capsule, or the presacral venous plexus; postoperative small bowel obstruction; stomal complications; wound infection, wound dehiscence, and abdominal compartment syndrome; the acute respiratory distress syndrome (ARDS); and the multiple organ dysfunction syndrome (MODS).

Figure 14. CT scan: marked thickening of sigmoid wall

Figure 15. High-grade retrograde obstruction

Large bowel obstruction secondary to diverticulitis can lead to considerable morbidity and may necessitate surgical intervention.⁵⁵ The obstruction is usually partial [see Figures 14 and 15], allowing preparation of the bowel in many cases. High-grade obstruction represents a complex problem. If the cecum is dilated to a diameter of 10 cm or greater and there is tenderness in the right lower quadrant, expeditious surgery is necessary because of the risk of cecal necrosis and perforation. High-grade obstruction with fecal loading of the colon is usually managed by performing a Hartmann procedure, though on-table lavage may be considered.²² A survey of GI surgeons in the United States indicated that 50% would opt for a one-stage procedure in low-risk patients with obstruction, whereas 94% would opt for a staged procedure in high-risk patients.⁵⁹

Small bowel obstruction may also complicate the clinical picture. Mechanical small bowel obstruction may occur as a consequence of adherence of the small bowel to a focus of diverticulitis, especially in the presence of a large pericolic abscess. Whereas small bowel obstruction tends to cause periumbilical crampy abdominal pain and vomiting, these characteristic manifestations may be obscured in part by pain attributed to diverticulitis. The concern in this situation is that ischemic small bowel may be ignored, with potentially disastrous consequences. Diarrhea should trigger the suspicion of colonic disease, and formation of a fistula into the small bowel should raise the possibility of Crohn disease. CT scanning often helps the surgeon differentiate between primary and secondary small bowel obstruction, but ultimately, exploratory surgery may be required both for diagnosis and for treatment.

Lower GI bleeding caused by diverticular disease rarely calls for emergency resection, because the bleeding is self-limited in most patients (80% to 90%). Furthermore, active diverticulitis is rare when active bleeding is the presenting symptom. Attempts are made to establish the active bleeding site by means of colonoscopy, tagged red blood cell nuclear scans, or angiography; barium contrast studies have no role to play in this situation. Emergency resection is indicated if the bleeding is life-threatening and if colonic angiography and attempted superselective embolization prove unsuccessful. In an unstable patient, total abdominal colectomy is necessary if the site of bleeding is unknown, though identification of the bleeding site with intraoperative colonoscopy has been reported. In a stable patient with ongoing bleeding, repeat angiography at a later time is appropriate, or so-called pharmacoangiography (infusion of heparin) can be employed in an attempt to induce bleeding.

Cecal Diverticulitis

Figure 16. Classification of pathologic types of cecal diverticulitis

In the United States, diverticulitis rarely involves the cecum or the right colon. Right-side diverticula occur in only 15% of patients in Western countries, compared with 75% in Singapore.¹ The incidence of cecal diverticulitis appears to be related to the number of diverticula present.⁶⁰ A classification system has been proposed that divides cecal diverticulitis into four grades [see Figure 16] to facilitate comparisons between different clinical series and to help surgeons formulate treatment plans in the OR.⁶⁰ Some cecal diverticula are true diverticula, containing all layers of the bowel wall, but the majority are pseudodiverticula. Diverticulitis of the hepatic flexure and the transverse colon is even less common and can present with symptoms suggesting appendicitis.^61,62

Figure 17. CT scan: inflammation in the pericecal area

Patients with right-side disease tend to be younger and to have less generalized peritonitis than patients with left-side diverticulitis.^60,61 Because they typically present with right lower quadrant pain, fever, and leukocytosis, acute appendicitis is usually suspected. CT scans are helpful for differentiating cecal diverticulitis from appendicitis or colon cancer [see Figure 17].^63,64 If cecal diverticulitis is suspected (as in a patient who has previously undergone appendectomy or in a patient with known right-side diverticulosis who has experienced similar attacks in the past), medical management with observation and antibiotics is generally the favored strategy, just as with simple sigmoid diverticulitis. In Japan, where right-side diverticulitis is more common, medical treatment has been successfully used for recurrent attacks of uncomplicated right-side diverticulitis.⁶⁵ After a few weeks, colonoscopy should be performed to rule out a colonic neoplasm.

If the patient has significant peritonitis or the diagnosis is unclear, laparoscopy or laparotomy is indicated. It is important that one or the other be done because the mortality associated with delayed treatment of perforated cecal diverticulitis is high. In our institution, laparoscopy is usually employed; if the diagnosis is unclear, laparotomy is recommended. When inflammation is localized and minimal, colectomy is unnecessary, and incidental appendectomy should be considered if the cecum is uninvolved at the base of the appendix.⁶⁶ If desired, the diverticulum may be removed as well.

Diverticulectomy should be done only if (1) carcinoma can be ruled out, (2) the resection margins are free of inflammation, (3) the ileocecal valve and the blood supply of the bowel are not compromised, and (4) perforation, gangrene, and abscess are absent.⁶⁰ Localized diverticulectomy, in general, should be reserved for grade I and grade II disease.⁶⁰ Sometimes, the ostium of the inflamed diverticulum is palpable if the cecum is mobilized surgically.⁶⁷ On-table cecoscopy thorough the appendiceal stump has also been helpful in establishing the diagnosis in the OR.⁶⁶ Grade III and IV cecal diverticulitis may be difficult to differentiate from carcinoma; resection is favored for these lesions.⁶⁷ An anastomosis may be created if contamination is limited, but generally, primary resection, ileostomy, and a mucous fistula are favored for treatment of grade IV disease.

Diverticulitis in patients younger than 40 years has been a focus of considerable attention in the literature, though this group only represents about 2% to 5% of the patients in large series.³¹ The incidence of diverticulitis in young patients may be increasing, and obese Latino men appear to be at particular risk.⁶⁸ This predominance in males reflects a tendency to underdiagnose acute diverticulitis in young women.⁶⁹ Some authors have asserted that diverticulitis is particularly virulent in young patients; however, current data tend not to support this concept, suggesting that patients with mild diverticulitis are misdiagnosed when hospitalized or are treated as outpatients. The high rate of early operation in young patients probably reflects misdiagnosis of diverticulitis as acute appendicitis rather than the development of particularly severe forms of diverticulitis.⁶⁸ Patients found to have uncomplicated acute diverticulitis may, if desired, undergo incidental appendectomy in conjunction with medical treatment of diverticulitis.

Unlike elderly patients, hospitalized young patients with diverticulitis tend to have few comorbidities other than obesity. Furthermore, young patients hospitalized for diverticulitis tend to have relatively advanced disease, perhaps as a consequence of delayed diagnosis,² whereas elderly patients hospitalized with an admitting diagnosis of diverticulitis tend to exhibit a wider spectrum of disease severity. Young patients appear not to have a higher rate of recurrent diverticulitis than older patients do, and thus, aggressive resection is not necessary at the time of the first attack.^42,68 However, a finding of advanced diverticulitis on CT scans is a predictor of subsequent disease complications in this population.^70,71

In general, diverticulitis should be approached in the same fashion in younger patients as in older patients.⁷¹ The pathophysiology of the disease is probably identical. As in the elderly, elective resection is recommended after recurrent attacks, not after a single attack; with follow-up, the majority of patients hospitalized with acute diverticulitis do not require operation.^71,72

In view of their known predisposition to infection, immunocompromised patients (e.g., chronic alcoholics, transplant patients, and persons with metastatic tumors who are receiving chemotherapy) with diverticulitis are at particular risk. There is no evidence that the incidence of diverticulitis is higher in this population than in the general population, but it is clear that immunocompromised patients have higher rates of operation once diverticulitis develops and that their postoperative mortality is higher.^73,74 Corticosteroid intake causes a number of significant problems, such as thinning of the colonic wall, lessening of the physical findings with diverticulitis, and an attenuated inflammatory response.

Any immunocompromised patient with abdominal pain should be evaluated aggressively. Contrast-enhanced CT is the imaging study of choice. The risk of perforation is increased in this setting, as is the risk of postoperative complications such as wound dehiscence. For an immunocompromised patient who has recovered from an episode of symptomatic diverticulitis, elective surgical treatment is recommended. A renal transplant patient with asymptomatic diverticulosis, however, need not undergo prophylactic colectomy. Pretransplantation colonic screening of patients older than 50 years does not reliably predict postransplantation colonic complications.⁷⁵

Diverticulitis may give rise to various unusual manifestations involving multiple organ systems [see Table 1]. Not surprisingly, immunocompromised patients are at particular risk.

Retroperitoneal abscesses can track into anatomic planes (e.g., along the psoas muscle) or through the obturator foramen to areas such as the neck, the thigh,⁷⁶ the knee, the groin,⁷⁷ and the genitalia.^78,79 CT scanning is essential to outline the extent of such abscesses. Contrast enemas show the diverticula along with a sinus tract into the abscess cavity. Cultures of the abscess demonstrate the presence of colonic organisms such as Bacteroides fragilis. Definitive treatment consists of wide abscess drainage and colon resection. Without aggressive surgical management, mortality is high.

The protean manifestations of diverticulitis also include pylephlebitis (which causes liver abscesses), arthritis, and skin changes. Diverticulitis has in fact replaced appendicitis as the most common source of liver abscesses of portal origin. Simple abscesses may be drained percutaneously if they are not too large, and multiple loculated abscesses may be managed with open drainage. The main risk factors for mortality from liver abscesses are immunosuppression, underlying malignancy, the presence of multiple organisms, and liver dysfunction. If the decision is made to perform a colectomy, the procedure may be done after drainage of the liver abscess or simultaneously with drainage during an open procedure.

An anatomic curiosity sometimes encountered in patients with diverticular disease is a giant diverticulum, also termed a giant gas cyst or a pneumocyst of the colon.⁸⁰ These lesions, which may reach diameters of 40 cm, are believed to develop as a consequence of a ball-valve mechanism created by intermittent occlusion of the neck by fecal material that traps air in the diverticulum. Most giant diverticula are minimally symptomatic, causing only mild abdominal pain, and perforation is rare. A mobile mass may be palpable, and the gas-filled cyst can be seen on plain abdominal films. As many as two thirds of giant diverticula are opacified during a barium enema and can thereby be differentiated from other abnormalities (e.g., a mesenteric cyst, emphysematous cholecystitis, or a colon duplication). The cyst tends to adhere densely to adjacent structures (e.g., the bladder and the small bowel). The treatment of choice is resection of the colon and the cyst; performing diverticulectomy alone can lead to the development of a colocutaneous fistula.

Recurrent diverticulitis is rare after a colectomy for diverticulitis, occurring in 1% to 10% of patients.⁸¹ As many as 3% of patients who have undergone resection for diverticulitis will require repeat resection.³ The differential diagnosis includes Crohn disease, irritable bowel syndrome, carcinoma, and ischemic colitis. CT imaging and colonoscopy should be carried out. Particular care should be taken to review pathologic specimens for evidence of Crohn disease.

The only significant determinant of recurrent diverticulitis is the level of the anastomosis; the high pressure in the sigmoid colon distal to the anastomosis appears to be responsible. In one study, the risk of recurrence was four times greater in patients with a colosigmoid anastomosis than in those with a colorectal anastomosis.⁸² Reoperation requires a dissection that commences in noninflamed tissue. Dissection may be particularly difficult near the pelvic sidewall because of fibrosis; ureteral stenting may facilitate identification of the ureters.

A small number of patients experience recurrent episodes of left lower quadrant abdominal pain that are not accompanied by the classic findings of acute diverticulitis (e.g., fever and leukocytosis). The inflammatory changes associated with diverticula in this subgroup have been referred to as atypical, subacute, or smoldering diverticulitis.^83,84 In this setting, there is not always a direct association between endoscopic and clinical findings; endoscopic evidence of diverticular inflammation has been seen in asymptomatic patients.⁸⁵ It has been suggested that there is a relation between diverticular disease and colitis.⁸⁶ Patients with chronic lower abdominal pain should undergo imaging studies and endoscopic evaluation, and other disorders (e.g., irritable bowel syndrome, inflammatory bowel disease, drug-induced symptoms, and bowel ischemia) should be excluded. In most cases of atypical diverticulitis, endoscopic findings are normal.⁸⁴ In carefully selected patients, colectomy often eliminates the abdominal pain, and many of these patients are eventually found to have histologic signs of acute and chronic mucosal inflammation.⁸⁴