Diverticular Disease

Summary

• Colonic diverticula are acquired outpouchings of mucosa and connective tissue through the colonic wall, found in around 75% of people over 70 in the Western world, overwhelmingly in the sigmoid colon [1][2].
• Most diverticular disease is asymptomatic (diverticulosis), but 10–30% develop symptomatic complications ranging from painful diverticular disease to diverticulitis, abscess, perforation, fistula, stricture and haemorrhage [1].
• Management is chiefly medical, with surgery reserved for complications or recurrent, refractory disease [1][2].

Definition

• Diverticula are hollow outpouchings of the gastrointestinal tract.
• Congenital diverticula (for example Meckel's) contain all three coats of the bowel wall; acquired diverticula, as in sigmoid diverticular disease, lack a muscularis layer [1].
• Sabiston frames the same distinction as "true" versus "false": true diverticula contain all layers of the bowel wall and are rare and usually congenital, while the vast majority of colonic diverticula are false (pulsion, pseudodiverticula) containing only mucosa and muscularis mucosa [4].

Pathophysiology

• Diverticula form along the lines where penetrating colonic arteries traverse the colonic wall between the taeniae coli, associated with hypertrophy of the surrounding colonic muscle and mucosal thickening, probably driven by high-pressure colonic contractions causing chronic wall pressure [2].
• Epidemiological evidence links the disease to a refined, fibre-deficient Western diet: altered collagen structure with ageing, disordered motility and raised intraluminal pressure (especially in the narrow sigmoid colon) cause mucosal herniation at vessel-penetration points; the rectum, with a complete muscular coat and wider lumen, is rarely affected.
• Diverticular disease is rare in Africa and Asia, where dietary fibre intake is high (Burkitt) [1].
• Diverticulitis represents acute neutrophilic infiltration around an inflamed diverticulum and in the subserosal tissues [2].

Why most diverticulitis stays localised

• Diverticula form classically on the mesenteric side of the colonic wall where the vasa recta traverse the muscular layer; these small vessels are the weak spots.
• When pressure, inflammation, impaired blood supply or trauma acts at these points it can perforate the diverticulum, producing infection and a marked local inflammatory response.
• Because most perforations occur on the mesenteric side, the surrounding mesentery acts as a natural barrier, containing the infection and allowing an abscess to form within the mesenteric tissues rather than spilling into the peritoneal cavity, which is why the majority of diverticulitis is contained.
• If the process outruns that barrier, generalised peritonitis and sepsis follow [4].

The mechanism of diverticulitis itself is thought to be obstruction of the orifice of a diverticulum, with stasis leading to bacterial overgrowth, inflammation and raised intradiverticular pressure, causing ischaemia and microperforation [4].

One anatomical fact has a direct operative consequence. The sigmoid and descending colon are typically affected while the rectum, having an extra layer of muscle, is generally spared, which is why the distal anastomotic margin in operations for diverticulitis should always be within the rectum, to reduce the likelihood of recurrence [4].

The pulsion mechanism and the segmentation theory in Schwartz's account

• Most colonic diverticula are false diverticula in which mucosa and muscularis mucosa herniate through the colonic wall between the teniae coli, at the points where the nutrient arterial vessels penetrate and presumably weaken the muscle; they are pulsion diverticula produced by high intraluminal pressure, whereas true diverticula containing all wall layers are rare and usually congenital [6].
• The most accepted theory is that a low-fibre diet yields small stool volume, which demands high intraluminal pressure and high wall tension for propulsion; chronic contraction then causes muscular hypertrophy and segmentation, in which the colon behaves as separate compartments rather than a continuous tube, so that pressure is directed radially against the wall instead of into propulsive waves (with an age-related loss of tensile strength and elasticity also proposed) and although none of these theories is proven, a high-fibre diet does appear to lower the incidence of diverticulosis [6].
• Half of the population over 50 in the United States and Europe is estimated to have colonic diverticula, the sigmoid is the commonest site, most cases are asymptomatic, and diverticulitis is estimated to occur in 10–25% of people with diverticulosis, resulting from macroscopic or microscopic perforation of a diverticulum with pericolic contamination [6].

Clinical features

Most diverticular disease is asymptomatic and found incidentally [1]. Recognised presentations include [1][2]:

• Painful diverticular disease: intermittent left iliac fossa pain, distension, flatulence and a sensation of heaviness, which may overlap with irritable bowel syndrome.
• Acute diverticulitis: persistent left iliac fossa pain (occasionally right-sided if a redundant sigmoid loop lies across the midline), fever, tachycardia and localised tenderness or a tender mass; diarrhoea or constipation may accompany it.
• Haemorrhage: typically painless, sudden and profuse, with large-volume dark red or clotted blood (bright red from the sigmoid, darker from the right colon), due to rupture of a peridiverticular submucosal vessel, usually without inflammation.
• Complications: pericolic or paracolic abscess (swinging fever, tender left iliac fossa mass), purulent or faeculent peritonitis from perforation, colovesical fistula (recurrent UTI, pneumaturia) or colovaginal fistula (faeculent vaginal discharge, more common after hysterectomy), and stricture (recurrent colicky pain, distension, bloating from chronic fibrosis).

Fistulae

• Fistulae result from local inflammation and abscess formation decompressing into a neighbouring organ.
• The most common, especially in men, is a colovesical fistula to the dome of the bladder, presenting with recurrent and often polymicrobial urinary tract infections, with pneumaturia and faecaluria; CT can reveal air or contrast in the bladder in the absence of prior instrumentation, and cystoscopy usually discloses inflammation at the fistula site. Colovaginal fistulae occur almost exclusively in women who have had a previous hysterectomy, presenting with vaginal discharge and passage of air per vagina.
• Colocutaneous fistulae usually present at a previous drain site after percutaneous drainage.
• Patients with fistulae usually do not need emergency surgery, because the abscess has already decompressed through the fistula [4].

Obstruction, fistula frequency and the differential in Schwartz's figures

• Obstructive symptoms occur in approximately 67% of patients with acute diverticulitis and complete obstruction in 10%; approximately 5% of patients with complicated diverticulitis develop a fistula to an adjacent organ, colovesical being commonest, then colovaginal and coloenteric, with colocutaneous fistulae rare [6].
• Diverticular bleeding, from erosion of the peridiverticular arteriole, can be massive but stops spontaneously in 80%; most significant lower gastrointestinal haemorrhage occurs in elderly patients in whom diverticulosis and angiodysplasia coexist, so the exact source may be difficult to identify [6].
• Giant colonic diverticula are extremely rare, usually on the antimesenteric side of the sigmoid, may be asymptomatic or cause vague pain, nausea or constipation, are suggested on plain radiographs and usually diagnosed by barium enema, and can perforate, obstruct or undergo volvulus, so resection of the involved colon with the diverticulum is recommended [6].
• The differential diagnosis of diverticulitis includes malignancy, ischaemic colitis, infectious colitis and inflammatory bowel disease, and for a fistula it includes malignancy, Crohn's disease and radiation injury, in a previously irradiated patient a fistula is recurrent cancer until proved otherwise [6].

Etiology

• Low dietary fibre intake in Westernised populations is the principal implicated factor, combined with age-related collagen change, colonic dysmotility and raised intraluminal pressure [1].
• Right-sided diverticular disease predominates in South East Asia [1].
• Diverticulitis is thought to be mainly a disease of the modern world, coinciding with dietary changes after the Industrial Revolution, and its incidence has risen with increasing life expectancy because it predominantly presents in older individuals [4].

• The prevalence figures are worth holding beside the risk of ever developing diverticulitis.
• Colonic diverticula are found in approximately 40% of individuals aged 50 to 60 and in over 60% of those over 80, yet modern estimates indicate that fewer than 5% of patients with diverticulosis will develop diverticulitis [4].
• Because diverticulosis is so prevalent, however, the absolute burden is large: more than 2.7 million outpatient visits and over 200,000 inpatient admissions annually in the United States, at an estimated cost of more than $2 billion [4].

Diagnosis

• Elective diagnosis is usually by colonoscopy, though this incompletely assesses the number and extent of diverticula and carries perforation risk in a narrowed segment [1].
• Contrast-enhanced CT is the investigation of choice in the acute setting, with excellent sensitivity and specificity for bowel-wall thickening, abscess and extraluminal disease, and is used to guide percutaneous abscess drainage [1][7].
• Endoscopy and contrast studies are generally deferred for six weeks after an acute attack to reduce perforation risk, then used to exclude coexisting carcinoma [1][7].
• Hb, WCC and CRP are checked during acute episodes [1].

A colonic neoplasm can mimic diverticulitis, currently estimated at around 1% to 3% of cases overall and significantly higher against a background of complicated disease, which is why colonoscopy is recommended 4 to 8 weeks after recovery to exclude malignancy [4].

Imaging and endoscopy in Schwartz's account

• Plain radiographs detect free intra-abdominal air; CT defines pericolic inflammation, phlegmon or abscess, with uncomplicated disease showing pericolic soft-tissue stranding, wall thickening and/or phlegmon; contrast enema and endoscopy are relatively contraindicated in the acute setting because of the perforation risk [6].
• Because colon carcinoma can present identically, every patient must be evaluated for malignancy after the acute episode resolves, with colonoscopy recommended 4–6 weeks after recovery, and inability to exclude malignancy is itself an indication for resection [6].
• For a fistula the two key tasks are defining its anatomy and excluding other diagnoses: contrast enema and/or small-bowel studies map the tract, CT identifies associated abscesses or masses, and colonoscopy or sigmoidoscopy is usually needed to rule out malignancy [6].

Scoring and Severity

• The Hinchey classification grades the severity of complicated diverticulitis and peritoneal contamination and guides management: Grade I (mesenteric or pericolic abscess; Grade II) pelvic (walled-off) abscess; Grade III (purulent peritonitis; Grade IV) faecal peritonitis [1][7].
• Mortality is markedly higher with perforation than with an inflammatory mass alone (33% versus 3%) [1].
• Complicated diverticulitis is characterised by the presence of an abscess, fistula, obstruction or free perforation [4].

The Hinchey stages as Schwartz defines them

Schwartz states the Hinchey system as follows: stage I is colonic inflammation with a pericolic abscess, stage II colonic inflammation with a retroperitoneal or pelvic abscess, stage III purulent peritonitis and stage IV faecal peritonitis [6].

Treatment and Management

• Medical: a high-fibre diet, bulk-forming laxatives and stool softeners are commonly recommended, though evidence for effectiveness is limited; antispasmodics may help recurrent pain [1].
• Uncomplicated diverticulitis confirmed on CT in an immunocompetent patient without systemic infection may not require antibiotics, as it may be self-limiting; complicated disease with a localised abscess is treated with intravenous antibiotics and image-guided percutaneous drainage [1][8].
• In the Oxford Handbook emergency protocol, uncomplicated diverticulitis is treated with a low-residue diet, high fluid intake and stool softeners for two weeks, with intravenous antibiotics such as co-amoxiclav with or without gentamicin reserved for infective exacerbations [7].
• Recurrent infective episodes may be reduced by cyclical antibiotics and probiotics [2].

Most patients with uncomplicated diverticulitis can be managed as outpatients, with pain medication, short-term dietary alteration (clear liquids then a low-residue diet until inflammation subsides) and, traditionally, antibiotics. A systematic review and meta-analysis found that antibiotics in uncomplicated diverticulitis do not accelerate recovery, prevent complications or prevent subsequent surgery, and some physicians have accordingly stopped prescribing them; outpatient management has been found safe and cost-effective with low readmission rates [4].

Outpatient and inpatient care, and the case for elective resection in Schwartz's account

• Most uncomplicated diverticulitis responds to outpatient broad-spectrum oral antibiotics for 7–10 days with a low-residue diet; about 10–20% with more severe pain, fever and leukocytosis are admitted for parenteral antibiotics and bowel rest, most improving within 48–72 hours, and failure to improve suggests abscess, for which CT is invaluable and many pericolic abscesses can be drained percutaneously [6].
• Most patients recover without surgery and 50–70% have no further episodes; the traditional advice of elective sigmoid colectomy after the second episode, after the first in very young patients and after any complicated episode has been questioned, since more recent studies suggest the risk of complications and emergency resection does not rise with recurrence, so resection rates have fallen and many surgeons no longer advise colectomy even after two documented episodes if the patient is asymptomatic and carcinoma has been excluded, immunosuppressed patients being the exception, still advised colectomy after a single documented episode [6].
• Abscesses under 2 cm may be treated with parenteral antibiotics alone; larger abscesses are best treated with CT-guided percutaneous drainage and antibiotics, which may allow a one-stage elective procedure or obviate colectomy altogether if recovery is complete [6].
• Incomplete obstruction often responds to fluid resuscitation, nasogastric suction and gentle low-volume water or Gastrografin enemas, allowing full bowel preparation and elective resection, whereas a high-volume oral bowel preparation is contraindicated with obstructive symptoms and obstruction not rapidly relieved mandates laparotomy [6].
• Diverticular haemorrhage is managed by resuscitation and localisation as for lower gastrointestinal bleeding; colonoscopy may occasionally identify a bleeding diverticulum treatable by adrenaline injection or cautery, angiography may be diagnostic and therapeutic, and persistent or recurrent bleeding rarely requires laparotomy and segmental colectomy [6].

Surgeries

• Emergency laparotomy: for generalised peritonitis or failure to respond to optimum medical therapy; carries substantial risk (mortality around 15% overall, approaching 50% with faecal peritonitis) [1].
• Hartmann's procedure: sigmoid resection with formation of a left iliac fossa end-colostomy and closure of the rectal stump; often the safest option with significant contamination or an unstable patient, with a second-stage reversal planned later [1][2].
• Resection with primary anastomosis, with or without defunctioning loop ileostomy: considered selectively in a young, fit patient with limited contamination; evidence suggests outcomes are better than a simple defunctioning stoma without resection [1].
• Laparoscopic lavage: in selected, stable cases in expert hands (Hinchey 2–3) without gross faecal contamination or visible perforation; remains controversial [1][7].
• Elective sigmoid colectomy: considered for recurrent attacks, symptoms affecting quality of life, stricture, or fistula; a laparoscopic approach is favoured where feasible [1]. The aim is to remove the affected segment and perform primary anastomosis of healthy bowel: the proximal margin should be in soft, pliable bowel, and it is not necessary to include all proximal diverticula, but the distal anastomosis should be to the upper rectum, because leaving a segment of distal sigmoid is associated with a higher risk of recurrent diverticulitis. Minimally invasive surgery is safe with faster return of bowel function, less pain and shorter stay, and ureteric stents are often used to mitigate ureteric injury risk by serving as guides amid inflamed tissues [4].
• Percutaneous drainage: for stable patients with a localised abscess (Hinchey I–II), avoiding laparotomy [1].
• Fistula surgery: for colovesical fistula, once malignancy is excluded, the sigmoid is resected off the bladder with catheter drainage for 7–10 days, sometimes with an omental interposition flap; ureteric stents may aid safe dissection [1]. Initial management of any diverticular fistula is broad-spectrum antibiotics to reduce inflammation, followed by colonoscopy and appropriate imaging such as cystoscopy to exclude malignancy and Crohn disease, then resection of the involved colon and fistula tract with primary anastomosis [4].

Extent of resection and operative choices in Schwartz's account

• In the elective setting sigmoid colectomy with primary anastomosis is the procedure of choice, increasingly laparoscopic; the distal resection must always extend to the rectum because recurrence is high if any sigmoid is retained, the proximal extent must include all thickened or inflamed bowel, but resection of every diverticulum is unnecessary [6].
• Urgent laparotomy is required when an abscess is inaccessible to percutaneous drainage, when the patient deteriorates or fails to improve, or with free air or peritonitis, and in almost all cases the affected segment should be resected: Hinchey I–II patients may be candidates for a one-stage sigmoid colectomy with primary anastomosis, while larger abscesses, peritoneal soiling or peritonitis are most commonly treated by sigmoid colectomy with end colostomy and Hartmann's pouch [6].
• Sigmoid colectomy with primary anastomosis, with or without on-table lavage, protected by a loop ileostomy has also succeeded and suits stable patients, its great advantage being that restoring continuity is simpler than taking down a Hartmann's pouch; the same option applies in obstruction when the patient is stable and proximal and distal bowel look healthy, though sigmoid colectomy with end colostomy remains the safest operation there [6].
• Inflammation and phlegmon raise the risk of ureteric injury during sigmoid mobilisation, so preoperative ureteric catheters can be invaluable; proximal diversion with local drainage alone is reserved for extremely unstable patients or inflammation so severe that resection would harm adjacent organs, and is generally avoided for its high morbidity, mortality and need for multiple operations, while laparoscopic lavage and drainage without resection has been reported safe even with free perforation but carries an expected 20% reoperation rate [6].
• Fistula surgery, once anatomy is defined and other diagnoses excluded, comprises resection of the diverticular segment (usually with primary anastomosis) and simple repair of the secondarily involved organ, with suspicion of carcinoma mandating a wider en bloc resection [6].
• Right-sided diverticula, commoner in younger patients and in people of Asian descent, are usually asymptomatic but when inflamed mimic appendicitis and are often diagnosed only in the operating room; a diverticulectomy may be done for a single large diverticulum with minimal inflammation, but ileocaecal resection is usually preferred [6].

Complications

• Diverticulitis, pericolic or paracolic abscess, purulent or faeculent peritonitis, intestinal obstruction, haemorrhage and fistula formation (colovesical, colovaginal, colocutaneous, or rarely to the retroperitoneum causing a psoas abscess) are recognised complications of diverticular disease [1].
• Patients who present with a diverticular abscess often experience recurring episodes, and both recurrence risk and complication risk are increased in that group; the most recent American Society of Colon and Rectal Surgeons guidelines recommend considering elective resection after successful non-operative treatment of a diverticular abscess, on moderate-quality evidence [4].
• Patients with abscesses not amenable to percutaneous drainage and unresponsive to treatment require urgent surgery [4].

Prognosis

Most diverticulosis remains asymptomatic lifelong. After a first episode of diverticulitis, roughly 25% of patients under 50 will have a further episode, but 75% will not, and the complication rate after elective surgery is low; the risk of complications does not clearly increase with recurrent attacks, which has shifted practice toward more conservative, individualised management [1][8].

The rationale for that shift is worth stating explicitly. After an initial episode of acute uncomplicated diverticulitis only 10% to 35% of individuals have another episode, and although the chance of recurrence rises after further episodes, recurrences generally tend to follow the severity of the initial episode, so the number of attacks of uncomplicated diverticulitis is no longer accepted as a standalone indication for elective resection, as it once was [4].

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