Acute diverticulitis
Left lower pain, fever and raised CRP in an older patient. Not every case needs antibiotics; every patient needs the colon checked afterwards.
A 62-year-old woman has had left lower abdominal pain for 3 days with fever 38.2 °C. Tender in the left iliac fossa with guarding there only. Pulse 98, BP 128/80. WBC 15,000/µL, CRP 140 mg/L.
A week later, a 70-year-old man arrives with similar pain, but now with rigidity across the whole abdomen, pulse 124 and BP 88/56.
How do you tell simple from complicated diverticulitis, and which of these patients goes home?
- Assess severityObservations, sepsis screen, peritonism (local or generalised).
- BloodsFBC, CRP, U&E, LFT, lactate, group and save if unwell.
- CT abdomen and pelvis with contrastConfirms the diagnosis and shows abscess or perforation.
- Uncomplicated and wellOral fluids, analgesia, home with safety-net. Antibiotics only if unwell, immunosuppressed or comorbid.
- ComplicatedAdmit, IV fluids, IV antibiotics, nil by mouth if needed.
- Generalised peritonitis or shockSepsis bundle, surgeons now.
- Follow upColonoscopy or CT colonography at 6–8 weeks after a first episode if not recently done.
- Generalised peritonitis
- Shock or lactate above 2
- Free air on X-ray or CT
- Abscess on CT
- Rectal bleeding with instability
- Failure to improve in 48–72 hours
- Perforation
- Colorectal cancer mimicking diverticulitis
- Ovarian or ectopic pathology in women
- Ischaemic colitis
- Fistula (pneumaturia, faecal vaginal discharge)
| Uncomplicated | Localised inflammation, no abscess or perforation |
| Hinchey I | Small pericolic abscess |
| Hinchey II | Pelvic or distant abscess |
| Hinchey III | Purulent peritonitis |
| Hinchey IV | Faecal peritonitis |
| Abscess over 3–4 cm | Usually percutaneous drainage |
| CRP above 150 mg/L | Higher chance of complications |
Check every dose against a current drug reference and your hospital protocol.
On this page
Background
Diverticula are pouches of mucosa through weak points in the colon wall where vessels enter. They are most common in the sigmoid. Diverticulosis is common with age; diverticulitis is inflammation, usually from a blocked diverticulum.
History and examination
- Left iliac fossa pain, often for days.
- Fever, nausea, change in bowel habit.
- Urinary symptoms if the inflamed colon lies on the bladder.
- Pneumaturia or faecaluria: colovesical fistula.
- Examination: LIF tenderness, guarding, sometimes a mass. Generalised rigidity means perforation.
- Women: pregnancy test, and consider gynaecological causes.
Severity and management
Home: analgesia, fluids, review in 48 hours if not better
Admit, IV fluids, antibiotics
- IV antibiotics
- drain if over 3–4 cm
Resuscitate, antibiotics, emergency surgery
Differential diagnosis
| Condition | Clues |
|---|---|
| Colorectal cancer | Weight loss, anaemia, longer history, mass on CT |
| Ovarian torsion or cyst | Sudden onset, ultrasound findings |
| Ectopic pregnancy | Positive pregnancy test |
| Ischaemic colitis | Older, vascular disease, bloody diarrhoea |
| Inflammatory bowel disease | Younger, chronic diarrhoea |
| Appendicitis (sigmoid on the right) | Right iliac fossa pain |
| Ureteric colic | Loin to groin pain, blood in urine |
Investigations
| Test | Why |
|---|---|
| FBC, CRP | Inflammation |
| U&E, LFT, lactate | Sepsis, kidney function |
| Pregnancy test | All women of childbearing age |
| Erect chest X-ray | Free air if perforation suspected and CT delayed |
| CT abdomen and pelvis with contrast | Diagnosis, abscess, perforation |
| Colonoscopy at 6–8 weeks | Exclude cancer after the first episode (not during the acute episode) |
Treatment
Special situations
- Immunosuppressed (steroids, transplant, chemotherapy): signs are blunted; lower threshold for CT and admission.
- Recurrent episodes: elective surgery is considered on an individual basis, not after a fixed number of attacks.
- Diverticular bleeding: painless, often heavy, from the right colon more than the left. Separate problem from diverticulitis.
Common mistakes
- Giving antibiotics to every well patient with uncomplicated disease.
- Skipping a pregnancy test in women.
- Doing a colonoscopy during the acute attack (perforation risk).
- Missing a cancer by not arranging follow-up colonic imaging.
- Missing a fistula (ask about bubbles in the urine).
Frequently asked questions
Do all patients with diverticulitis need antibiotics?
No. Well patients with uncomplicated diverticulitis can often be managed with analgesia and fluids. Antibiotics are used if unwell, immunosuppressed, comorbid or complicated.
What is the Hinchey classification?
I: pericolic abscess, II: pelvic or distant abscess, III: purulent peritonitis, IV: faecal peritonitis.
Why is colonoscopy done after diverticulitis?
To exclude colorectal cancer, which can look similar on CT. It is done 6–8 weeks later, not during the attack.
Where do diverticula most often occur?
In the sigmoid colon.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 62-year-old has left iliac fossa pain, fever and a raised CRP. What is the most likely diagnosis?
Answer: Acute diverticulitis. Diverticulitis typically affects the sigmoid colon in older adults.
- Appendicitis: Right-sided.
- Renal colic: No.
- Ovarian torsion: Less likely at this age.
- Cholecystitis: Right upper quadrant.
2. CT shows a 5 cm pericolic abscess in diverticulitis. What is the best management?
Answer: Drainage and antibiotics. Larger abscesses (over 3–4 cm) are drained percutaneously.
- Oral antibiotics at home: Too little.
- Immediate colectomy for all: Not first.
- Observation: No.
- Colonoscopy now: Risk of perforation.
3. Six weeks after diverticulitis, what investigation is recommended?
Answer: Colonoscopy. To exclude colon cancer that can mimic diverticulitis.
- Barium swallow: No.
- Repeat CT abdomen: Not the main aim.
- No investigation: Cancer must be excluded.
- Upper endoscopy: No.
4. A 60-year-old has left iliac fossa pain, fever and tenderness. CT shows sigmoid diverticulitis with a 2 cm pericolic abscess. He is stable. What is the management?
Answer: IV antibiotics and observation. Hinchey classification: I — pericolic abscess; II — pelvic/distant abscess; III — purulent peritonitis; IV — faecal peritonitis. Small abscesses (< 3–4 cm) respond to IV antibiotics; larger ones need percutaneous drainage. Generalised peritonitis (III/IV) needs surgery (Hartmann’s or resection with anastomosis). Colonoscopy 6 weeks later to exclude cancer.
- Emergency Hartmann’s procedure: Hartmann’s procedure is for generalised peritonitis, not a small contained abscess.
- Colonoscopy now: Colonoscopy in acute diverticulitis risks perforation.
- Discharge without antibiotics: An abscess needs antibiotics and monitoring.
5. A 65-year-old man has left iliac fossa pain, fever of 38.3 °C and tenderness in the LIF. CRP is 160 mg/L. CT shows sigmoid diverticulitis with a 3 cm pericolic abscess. What is the most appropriate management?
Answer: IV antibiotics + percutaneous drainage. Complicated diverticulitis with a localised abscess (Hinchey I–II) is managed with IV antibiotics and percutaneous drainage if the abscess is large enough (usually over 3–4 cm). Purulent or faecal peritonitis (Hinchey III–IV) needs surgery. Colonoscopy is delayed for 6–8 weeks to exclude cancer, because of perforation risk.
- Emergency Hartmann’s procedure today: Hartmann’s procedure is for generalised (purulent or faecal) peritonitis; a localised 3 cm abscess can be drained percutaneously.
- IV antibiotics alone: Usually enough for abscesses under ~3 cm; larger need drainage.
- Colonoscopy and biopsy: Risk of perforation in acute inflammation.
6. Persistence of which embryonic structure forms Meckel's diverticulum?
Answer: Vitellointestinal duct. The vitelline duct connects the midgut to the yolk sac and normally disappears by week 7. If its intestinal end persists, it forms Meckel's diverticulum on the antimesenteric border of the ileum. It may contain gastric or pancreatic tissue and bleed.
- Urachus: A patent urachus causes urine leaking from the umbilicus.
- Allantois: Becomes the urachus.
- Ductus arteriosus: Becomes the ligamentum arteriosum.
- Notochord: Becomes the nucleus pulposus.
7. A 65-year-old man has rows of sigmoid diverticula between the taeniae coli. Why do they form at these particular sites?
Answer: Vessels pierce the circular muscle there. Colonic diverticula are pulsion pseudodiverticula: mucosa and submucosa herniate through the muscle wall without a muscle coat. They form where the vasa recta penetrate the circular muscle, between the mesenteric taenia and the two antimesenteric taeniae. Low fibre diet produces small, hard stools and high segmental pressures, mostly in the narrow sigmoid. Because the herniation follows the vessel, diverticula can bleed briskly when the stretched vasa recta rupture. The rectum, with a complete longitudinal coat, is spared.
- The taeniae coli are thinnest there: Diverticula form between, not through, the taeniae.
- No muscularis mucosae is present there: The muscularis mucosae is present throughout the colon.
- Lymphoid follicles weaken the wall there: Not the weak point in the colon wall.
- Haustral folds are absent at these sites: Haustra are present in the sigmoid.
References and dose sources
- NICE NG147
- NICE NG12
- ACPGBI — diverticular disease resources
- Paracetamol dosing: Drugs.com: Acetaminophen (paracetamol) dosage (see also our paracetamol dose page)
- Co-amoxiclav (amoxicillin with clavulanic acid) dosing: Drugs.com: Amoxicillin/clavulanate dosage (see also our co-amoxiclav (amoxicillin with clavulanic acid) dose page)
- Ciprofloxacin dosing: Drugs.com: Ciprofloxacin dosage (see also our ciprofloxacin dose page)
- Ceftriaxone dosing: Drugs.com: Ceftriaxone dosage (see also our ceftriaxone dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.