Definition and epidemiology
Diverticulitis refers to inflammation and/or infection of one or more diverticula—sac-like outpouchings of the colonic wall. It represents a complication of diverticulosis, the presence of multiple diverticula, which is extremely common in Western populations.
Epidemiology: Diverticulosis affects approximately 30–40% of individuals over 60 years and more than 60% of those over 80 in Western countries. However, only about 4–5% of people with diverticulosis will develop diverticulitis during their lifetime. The incidence is rising in younger adults. In Western populations, diverticulitis predominantly affects the sigmoid and left colon, while right-sided diverticulitis is more common in Asian populations. Men and women are affected roughly equally, though some studies suggest a slight male predominance in younger patients.
- Diverticulitis is left lower quadrant pain, fever, and leukocytosis—called left-sided appendicitis
- CT abdomen/pelvis with IV contrast is the diagnostic test of choice (95% sensitive and specific)
- Colonoscopy is contraindicated acutely due to perforation risk; perform 6–8 weeks after resolution
- Uncomplicated diverticulitis can be managed outpatient; select cases may not require antibiotics
- Antibiotics must cover gram-negatives and anaerobes: ciprofloxacin plus metronidazole or amoxicillin-clavulanate
- Abscesses larger than 3–4 cm require percutaneous drainage plus antibiotics
- Hinchey IV (fecal peritonitis) requires emergency surgery, traditionally Hartmann procedure
- Routine elective resection after two episodes is outdated; decisions are now individualized
Etiology and risk factors
Diverticulitis develops when a diverticulum becomes obstructed, typically by inspissated fecal material (fecalith), leading to bacterial overgrowth, inflammation, and potential microperforation or frank perforation.
Risk factors:
- Age: Incidence increases markedly after age 40
- Low-fiber diet: Traditional teaching emphasizes this, though recent evidence is mixed
- Obesity: Strong independent risk factor for diverticulitis and complications
- Physical inactivity: Sedentary lifestyle increases risk
- Smoking: Increases risk and severity of disease
- NSAIDs and aspirin: May increase risk of perforation and bleeding
- Immunosuppression: Corticosteroids and other immunosuppressive medications
- Connective tissue disorders: Polycystic kidney disease, Ehlers-Danlos syndrome, Marfan syndrome
- Prior episodes: Recurrence occurs in 10–30% after first episode
Contrary to older teaching, nuts, seeds, and popcorn have not been shown to increase diverticulitis risk and dietary restrictions are no longer recommended.
Pathophysiology
Diverticula are pseudodiverticula—outpouchings of mucosa and submucosa through the muscular layer at points of weakness where vasa recta penetrate the colonic wall. They are acquired herniations resulting from increased intraluminal pressure and age-related weakening of the colonic wall.
Diverticulitis begins when the neck of a diverticulum becomes obstructed, most commonly by a fecalith. Obstruction leads to:
- Stasis and bacterial overgrowth within the diverticulum
- Compromised blood supply to the diverticulum wall
- Inflammation of the diverticulum and pericolic fat
- Microperforation or frank perforation with bacterial translocation
The inflammatory process may remain localized (simple diverticulitis) or progress to complications:
- Pericolic abscess: Contained perforation walled off by mesentery and omentum
- Fistula formation: Communication with adjacent organs (bladder, vagina, skin, small bowel)
- Free perforation: Purulent or fecal peritonitis
- Stricture: Chronic fibrosis from recurrent inflammation
- Obstruction: From acute inflammation or chronic stricture
The Hinchey classification grades severity from pericolic inflammation (stage 0–I) to purulent peritonitis (stage II–III) to fecal peritonitis (stage IV).
Clinical features
The classic presentation of acute diverticulitis includes:
Symptoms:
- Left lower quadrant pain: Most common location (70–90% of cases), corresponding to sigmoid involvement; may be suprapubic or right-sided if right colon affected
- Fever: Low-grade fever is typical; high fever suggests abscess or perforation
- Change in bowel habits: Constipation more common than diarrhea
- Nausea and anorexia: Common associated symptoms
- Urinary symptoms: Dysuria, frequency, or urgency may occur with bladder irritation
Physical examination:
- Left lower quadrant tenderness: Focal tenderness with or without guarding
- Palpable mass: May indicate phlegmon or abscess
- Peritoneal signs: Rebound tenderness, rigidity suggest perforation
- Fever and tachycardia: Present in most cases
- Rectal examination: May reveal tenderness or mass; check for occult blood
Atypical presentations:
- Right lower quadrant pain in right-sided diverticulitis (mimics appendicitis)
- Immunosuppressed patients may have minimal symptoms despite severe disease
- Elderly patients may present with confusion or generalized weakness
Complicated diverticulitis features:
- Colovesical fistula: Pneumaturia, fecaluria, recurrent UTIs
- Colovaginal fistula: Passage of stool or gas per vagina
- Free perforation: Severe diffuse abdominal pain, peritonitis, septic shock
Diagnosis
Diagnosis is based on clinical presentation supported by imaging. Laboratory and imaging findings help confirm diagnosis and assess severity.
Laboratory studies:
- Complete blood count: Leukocytosis (WBC typically 12,000–15,000) with left shift
- C-reactive protein: Elevated, useful for monitoring response to treatment
- Urinalysis: May show sterile pyuria with bladder irritation; bacteriuria if fistula present
- Blood cultures: If sepsis suspected
Imaging:
CT abdomen and pelvis with IV contrast is the diagnostic test of choice (sensitivity 95%, specificity 95%). Oral contrast is optional and may delay diagnosis. CT findings include:
- Diverticula: Multiple colonic outpouchings
- Pericolic fat stranding: Inflammatory changes in surrounding fat
- Bowel wall thickening: Focal thickening greater than 4 mm
- Abscess: Fluid collection with or without air
- Free air: Indicates perforation
- Fistula or obstruction: Complications
The modified Hinchey classification on CT guides management:
- 0: Clinically mild, no CT findings or mild wall thickening
- Ia: Pericolic inflammation or phlegmon
- Ib: Pericolic or mesocolic abscess
- II: Pelvic or distant abscess
- III: Purulent peritonitis
- IV: Fecal peritonitis
Ultrasound (sensitivity 85%) may be useful when CT contraindicated (pregnancy) or unavailable. Findings include bowel wall thickening, pericolic fat inflammation, and hypoechoic mass.
Colonoscopy is contraindicated in acute diverticulitis due to perforation risk. Perform colonoscopy 6–8 weeks after resolution to exclude malignancy (colorectal cancer can mimic diverticulitis) and confirm diverticulosis.
Differential diagnosis
The differential diagnosis of left lower quadrant pain with fever includes:
- Colorectal cancer: May present with similar symptoms; colonoscopy after resolution essential
- Inflammatory bowel disease: Crohn disease can mimic diverticulitis; look for skip lesions, fistulas
- Appendicitis: If right-sided diverticulitis or retrocecal appendix
- Infectious colitis: Campylobacter, Salmonella, Shigella, C. difficile; diarrhea more prominent
- Ischemic colitis: Sudden onset, bloody diarrhea, older patients with vascular disease
- Gynecologic conditions: Ovarian torsion, ectopic pregnancy, tubo-ovarian abscess, endometriosis
- Urologic conditions: Pyelonephritis, nephrolithiasis, cystitis
- Epiploic appendagitis: Self-limited focal fat inflammation, no fever or leukocytosis
- Colonic perforation: From other causes (cancer, trauma)
- Irritable bowel syndrome: Chronic symptoms, no fever or inflammatory markers
Key distinguishing features of diverticulitis include age over 50, known diverticulosis, left lower quadrant tenderness, fever, leukocytosis, and CT findings of pericolic inflammation.
Management
Management depends on severity, classified as uncomplicated (simple) or complicated diverticulitis.
Uncomplicated diverticulitis (Hinchey 0–Ia)
Outpatient management is appropriate for immunocompetent patients with mild symptoms, ability to tolerate oral intake, no significant comorbidities, and reliable follow-up.
- Diet: Clear liquid diet initially, advance as tolerated; complete bowel rest not routinely necessary
- Antibiotics: Recent guidelines suggest select patients with CT-confirmed uncomplicated diverticulitis may be managed without antibiotics. When used, treat for 7–10 days covering gram-negative rods and anaerobes:
- Oral: ciprofloxacin or levofloxacin plus metronidazole, OR amoxicillin-clavulanate, OR moxifloxacin
- Analgesia: Acetaminophen preferred; avoid opioids and NSAIDs if possible
- Follow-up: Reevaluate in 48–72 hours; lack of improvement warrants hospital admission and imaging
Inpatient management is indicated for inability to tolerate oral intake, failed outpatient treatment, immunosuppression, significant comorbidities, or uncertain diagnosis.
- NPO or clear liquids initially
- IV fluids for hydration
- IV antibiotics: Covering anaerobes and gram-negatives (e.g., ceftriaxone or ciprofloxacin plus metronidazole; piperacillin-tazobactam; ticarcillin-clavulanate; carbapenem)
- Pain control
- Serial abdominal examinations to detect deterioration
Most patients improve within 48–72 hours. Transition to oral diet and antibiotics when improving; typical hospital stay 3–5 days.
Complicated diverticulitis (Hinchey Ib–IV)
Abscess (Hinchey Ib–II):
- Small abscesses (less than 3–4 cm): IV antibiotics alone often successful
- Large abscesses (greater than 3–4 cm): Percutaneous CT- or ultrasound-guided drainage plus IV antibiotics
- Surgery if percutaneous drainage fails or is not feasible
Perforation with peritonitis (Hinchey III–IV):
- Resuscitation: Aggressive IV fluids, broad-spectrum antibiotics, ICU care
- Emergency surgery: Hinchey IV requires urgent laparotomy
- Surgical options:
- Hartmann procedure: Sigmoid resection with end colostomy and rectal stump (traditional approach)
- Primary resection with anastomosis: With or without diverting ileostomy (selected stable patients)
- Laparoscopic lavage: For Hinchey III (purulent peritonitis without fecal contamination); controversial, not widely adopted
Fistula, stricture, obstruction: Elective segmental colonic resection after acute inflammation resolves.
Elective resection
Indications for elective sigmoid resection are individualized. Consider after:
- Complicated diverticulitis (abscess, fistula, obstruction, perforation)
- Inability to exclude malignancy
- Immunosuppression or chronic kidney disease (higher risk of complications)
- Recurrent symptoms despite medical management affecting quality of life
Routine elective resection after two episodes is no longer recommended; decisions are individualized.
Prevention of recurrence
After acute episode resolves:
- High-fiber diet: 25–30 grams daily may reduce recurrence
- Physical activity: Regular exercise
- Maintain healthy weight
- Smoking cessation
- Avoid NSAIDs if possible
- Mesalamine and rifaximin: Some evidence for reducing recurrence, not standard of care
- Colonoscopy: Perform 6–8 weeks after acute episode to exclude malignancy
Complications and prognosis
Complications occur in approximately 15–25% of patients with diverticulitis:
- Abscess formation: Most common complication (15–20%)
- Perforation: Free perforation in 1–2%; associated with high mortality
- Fistula: Colovesical most common (65%), followed by colovaginal, coloenteric, colocutaneous
- Obstruction: Partial or complete bowel obstruction from inflammation or stricture
- Bleeding: Rare in acute diverticulitis (diverticular bleeding is separate entity)
- Sepsis: Systemic inflammatory response, organ dysfunction
- Chronic symptoms: Persistent abdominal pain after acute episode (post-diverticulitis syndrome)
Prognosis:
- Uncomplicated diverticulitis: Excellent prognosis with appropriate treatment; mortality less than 1%
- Complicated diverticulitis: Mortality 5–10% overall; up to 20–30% with Hinchey IV perforation
- Recurrence: Occurs in 10–30% after first episode; risk highest in first year
- Recurrence after second episode: Approximately 30–40%
- Surgery outcomes: Elective resection has low morbidity (10–15%) and mortality (less than 2%); emergency surgery carries 15–30% morbidity and 5–10% mortality
Factors associated with worse outcomes:
- Immunosuppression (corticosteroids, transplant recipients)
- Chronic kidney disease
- Connective tissue disorders
- Age and comorbidities
- Delayed diagnosis or treatment
- Free perforation at presentation
Most patients with uncomplicated diverticulitis recover fully with medical management. Quality of life typically returns to baseline after acute episode resolves.
DIVERTICULITIS features: Diverticula on CT, Immunosuppression risk factor, LLQ (Vermiform location left-sided), Elderly patients, Rigidity if perforated, Temperature elevated, Infection/Inflammation, CRP elevated, Unable to exclude cancer (needs scope later), Leukocytosis, Imaging (CT) is gold standard, Treatment includes bowel rest and antibiotics, Inspissated fecal matter (fecalith) obstructs, Stricture may result
Practice questions
1. A 68-year-old man presents with 2 days of left lower quadrant abdominal pain, fever to 38.3°C, and constipation. He has a history of diverticulosis diagnosed on prior colonoscopy. Physical examination reveals left lower quadrant tenderness without rebound or guarding. Laboratory studies show WBC 14,500/μL. Which of the following is the most appropriate next step in diagnosis?
2. A 72-year-old woman with CT-confirmed uncomplicated sigmoid diverticulitis is being discharged from the hospital after 3 days of IV antibiotics with clinical improvement. She is tolerating a regular diet and is afebrile with normal vital signs. In addition to completing a course of oral antibiotics, which of the following should be recommended?
3. A 55-year-old man with a 3-day history of left lower quadrant pain and fever presents to the emergency department with worsening symptoms. CT scan shows sigmoid diverticulitis with a 5-cm pericolic abscess. He is hemodynamically stable. Which of the following is the most appropriate initial management?
Frequently asked questions
What causes diverticulitis?
Diverticulitis occurs when a colonic diverticulum becomes obstructed by a fecalith (hardened stool), leading to bacterial overgrowth, inflammation, and sometimes perforation. Risk factors include age over 60, obesity, smoking, low-fiber diet, physical inactivity, and NSAID use. Contrary to older beliefs, nuts and seeds do not cause diverticulitis.
What are the first symptoms of diverticulitis?
The first symptoms typically include left lower quadrant abdominal pain (most common), low-grade fever, and change in bowel habits (usually constipation). Nausea, loss of appetite, and generalized abdominal discomfort may also occur. The pain is usually constant and may worsen over hours to days. Physical examination reveals focal tenderness in the left lower abdomen.
How is diverticulitis diagnosed?
Diverticulitis is diagnosed with CT scan of the abdomen and pelvis with IV contrast, which is 95% sensitive and specific. CT shows bowel wall thickening, pericolic fat stranding, diverticula, and any complications like abscess or perforation. Blood tests reveal leukocytosis and elevated CRP. Colonoscopy is contraindicated during acute episodes but should be performed 6–8 weeks later to exclude colon cancer.
Is diverticulitis curable?
Acute diverticulitis is very treatable with antibiotics and bowel rest, with most patients recovering fully. However, the underlying diverticulosis (presence of diverticula) is permanent. About 10–30% of patients experience recurrent episodes. High-fiber diet, exercise, and weight management may reduce recurrence. Surgical resection of the affected colon segment cures diverticulitis in that area but is reserved for complicated cases or recurrent symptomatic disease.
Diverticulitis vs diverticulosis—what is the difference?
Diverticulosis is the presence of multiple diverticula (outpouchings) in the colon wall and is usually asymptomatic. It affects 30–40% of people over 60. Diverticulitis is inflammation or infection of one or more diverticula, causing pain, fever, and complications. Only 4–5% of people with diverticulosis develop diverticulitis. Think of diverticulosis as the structural condition and diverticulitis as the acute inflammatory complication.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: K57
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.