Key Facts

Acute diverticulitis is the most common complication of diverticular disease, occurring when a diverticulum becomes inflamed and/or infected. It ranges from mild pericolic inflammation to life-threatening perforation with faecal peritonitis.

Epidemiology

Approximately 10-25% of patients with diverticulosis will develop diverticulitis in their lifetime. Incidence is rising, particularly in younger patients (<50 years). Hospital admissions for diverticulitis have increased by ~50% over the past 20 years. Left-sided predominance in Western populations; right-sided more common in Asian populations.

Aetiology

Diverticulitis occurs when a diverticulum becomes obstructed by a faecalith (inspissated faecal material), leading to:

• Increased intraluminal pressure within the diverticulum
• Mucosal erosion and microperforation
• Bacterial translocation and local inflammation
• Pericolic abscess formation if contained; peritonitis if free perforation

Risk factors for developing diverticulitis: obesity, smoking, NSAIDs/corticosteroids, immunosuppression, sedentary lifestyle.

Pathophysiology

The faecalith obstructs the narrow neck of the diverticulum → increased pressure → mucosal ischaemia → erosion → microperforation → pericolic inflammation. If the microperforation is contained by pericolic fat and mesentery, a localised abscess forms (Hinchey I-II). If containment fails, purulent peritonitis (Hinchey III) or faecal peritonitis (Hinchey IV) results. Chronic or recurrent inflammation can cause fibrosis leading to stricture, or fistula formation (colovesical most common — pneumaturia, faecaluria, recurrent UTIs).

Uncomplicated Diverticulitis

• Constant LIF pain (may be suprapubic or generalised)
• Fever (low-grade)
• Nausea ± vomiting
• Change in bowel habit (constipation or diarrhoea)
• LIF tenderness, may have localised guarding
• Palpable LIF mass (phlegmon)

Complicated Diverticulitis

• Abscess: swinging fever, persistent pain, palpable tender mass
• Perforation: sudden severe pain, generalised peritonism, sepsis
• Fistula: pneumaturia, faecaluria, recurrent UTIs (colovesical); faeculent vaginal discharge (colovaginal)
• Obstruction: colicky pain, distension, absolute constipation, vomiting

Red Flags

• Generalised peritonism (rigid abdomen, rebound tenderness)
• Sepsis (tachycardia, hypotension, fever >38.5°C, raised lactate)
• Pneumoperitoneum on imaging
• Failure to improve after 48-72 hours of appropriate treatment

Bedside

• Observations: temperature, pulse, BP, RR (sepsis screen)
• Abdominal examination: tenderness, guarding, peritonism, mass
• Urinalysis: exclude UTI; pneumaturia suggests colovesical fistula
• Pregnancy test: in women of childbearing age

Bloods

• FBC: leucocytosis
• CRP: raised (correlates with severity)
• U&Es: AKI (sepsis, dehydration)
• Lactate: raised in sepsis/ischaemia
• Blood cultures: if septic

Imaging

• CT abdomen/pelvis with IV contrast: gold standard (sensitivity >95%)
  • Findings: pericolic fat stranding, colonic wall thickening (>4 mm), diverticula, abscess, extraluminal air (perforation), fistula
  • Hinchey staging guides management
• AXR: limited utility; may show ileus or free air but CT is far superior
• USS: may show pericolic collection; operator-dependent; useful in thin patients

Special Tests

• Colonoscopy: CONTRAINDICATED in acute phase (perforation risk); perform 6-8 weeks post-episode
• CT colonography: alternative post-episode imaging to exclude malignancy
• Contrast enema (water-soluble): rarely used now; replaced by CT

Non-pharmacological

• Uncomplicated (mild): may manage in community — clear fluids progressing to low-residue diet, analgesia (paracetamol — avoid NSAIDs/opioids)
• Hospital admission: if unable to tolerate oral intake, significant fever/sepsis, immunosuppressed, failed outpatient management
• Nil by mouth + IV fluids: if severe/complicated

Pharmacological

• Uncomplicated diverticulitis:
  • Antibiotics: co-amoxiclav 625 mg TDS PO for 5-7 days; OR ciprofloxacin 500 mg BD + metronidazole 400 mg TDS
  • DIABOLO trial: showed no benefit of antibiotics over conservative management for uncomplicated diverticulitis — practice shifting towards no antibiotics in mild cases
• Complicated/severe:
  • IV antibiotics: piperacillin-tazobactam 4.5 g TDS; OR meropenem 1 g TDS if severe sepsis
  • IV fluids, analgesia, VTE prophylaxis
• Analgesia: paracetamol 1 g QDS; avoid NSAIDs (perforation risk) and opioids (constipation, increased intraluminal pressure)

Surgical/Interventional

• Percutaneous abscess drainage: CT-guided for collections ≥3 cm (Hinchey I-II); with IV antibiotics
• Emergency surgery (Hinchey III-IV):
  • Hartmann's procedure: sigmoid resection + end colostomy + rectal stump closure; standard emergency operation; reversal in ~60% at 3-6 months
  • Primary anastomosis ± defunctioning loop ileostomy: increasingly preferred in selected patients (lower stoma rates)
  • Laparoscopic lavage: debated for Hinchey III — LOLA/SCANDIV/LADIES trials showed conflicting results
• Elective sigmoid colectomy: after recovery from complicated diverticulitis, or after 2+ uncomplicated episodes if significantly impacting quality of life (laparoscopic preferred)

Referral Criteria

• Emergency surgical review: peritonism, sepsis, failure of conservative management
• Outpatient surgical review: recurrent episodes, complicated disease, fistula, stricture
• Colonoscopy at 6-8 weeks: to exclude malignancy (mandatory after first episode)

Uncomplicated diverticulitis resolves in >95% with conservative/antibiotic management. After one episode, ~20-30% have recurrence over 10 years. Complicated diverticulitis (Hinchey III-IV) carries mortality of 10-20%. Emergency Hartmann's procedure has ~15% mortality. Elective laparoscopic sigmoid colectomy has <2% mortality with good long-term outcomes. Colovesical fistula repair has >90% success rate.

Acute Diverticulitis Management Algorithm

Key Trials