Gastrointestinal & Hepatic · Topic 19 of 26

Diverticulitis

Gastrointestinal · colonic inflammation

Diverticulitis

Confirm it with CT, then sort uncomplicated from complicated: many low-risk patients need no antibiotics, large abscesses need drainage, free perforation needs surgery.

Key numbers

Drain abscesses over 3–4 cmabscess > 3–4 cm

Colonoscopy 6–8 weeks after complicated diverticulitis6–8 weeks

01 · The ruleUncomplicated, low-risk: antibiotics are optional

Immunocompetent, otherwise healthy patients with mild uncomplicated diverticulitis can be managed without antibiotics; give them for complicated disease, immunosuppression, sepsis, frailty, significant comorbidity or unsafe outpatient care.

02 · What it isComplicated: abscess, fistula, obstruction or perforation

Complicated diverticulitis means an abscess, fistula, obstruction or free perforation — about 12% of presentations; everything else is uncomplicated.

03 · DoDrain abscesses over 3–4 cm

Add CT-guided percutaneous (or EUS-guided) drainage to antibiotics for abscesses larger than 3–4 cm, abscesses not resolving on antibiotics, or clinical deterioration; multiloculated or inaccessible abscesses need surgery.

Presentation

What you'll see

Left lower quadrant pain, fever, tender sigmoidTypical presentation is left lower quadrant pain and tenderness, often a palpable sigmoid, with fever, nausea and sometimes urinary symptoms; right-sided disease causes right-sided pain.

Do right now

In this order

First moves

Confirm diverticulitis with CT abdomen and pelvis

→

Admit for sepsis, severe pain or immunosuppression

→

Uncomplicated, low-risk: antibiotics are optional

→

Drain abscesses over 3–4 cmabscess > 3–4 cm

→

Free perforation or feculent peritonitis: emergency surgery

Why each step

Confirm diverticulitis with CT abdomen and pelvisCT of the abdomen and pelvis (IV contrast when possible) is the diagnostic test of choice — essential at first presentation, in severe illness and whenever the diagnosis is uncertain; it also shows complications.

Admit for sepsis, severe pain or immunosuppressionHospitalize patients with moderate to severe pain, fever, marked leukocytosis or sepsis, complicated disease, inability to take fluids, or glucocorticoid use (higher perforation risk); give IV fluids and keep NPO if complicated.

Uncomplicated, low-risk: antibiotics are optionalImmunocompetent, otherwise healthy patients with mild uncomplicated diverticulitis can be managed without antibiotics; give them for complicated disease, immunosuppression, sepsis, frailty, significant comorbidity or unsafe outpatient care.

Drain abscesses over 3–4 cmAdd CT-guided percutaneous (or EUS-guided) drainage to antibiotics for abscesses larger than 3–4 cm, abscesses not resolving on antibiotics, or clinical deterioration; multiloculated or inaccessible abscesses need surgery.

Free perforation or feculent peritonitis: emergency surgeryFree perforation, or suspected feculent or generalized peritonitis on exam or imaging, requires immediate surgery.

Management

Orders

Most uncomplicated cases: outpatient, clear liquidsManage most uncomplicated diverticulitis as an outpatient: clear liquid diet for 2–3 days, advancing as pain settles.

Oral regimen: amoxicillin-clavulanate or metronidazole combinationWhen outpatient antibiotics are chosen, cover gram-negative rods and anaerobes for 7–10 days: amoxicillin-clavulanate, or metronidazole plus ciprofloxacin, a cephalosporin or TMP-SMX.

IV regimen covers gram-negatives and anaerobesInpatient IV options include metronidazole plus a cephalosporin or a fluoroquinolone, or a single agent such as piperacillin-tazobactam or ertapenem, chosen by severity and resistance risk.

Colonoscopy 6–8 weeks after complicated diverticulitisColonoscopy is recommended 6–8 weeks after complicated diverticulitis to exclude cancer; after uncomplicated disease, only if there are alarm features or screening is not up to date.

Red flags & don'ts

Avoid harm

Pneumaturia or fecaluria: colovesical fistula complicationColovesical fistula, the most common diverticular fistula, presents with pneumaturia or fecaluria; it is more common in women after hysterectomy. Chronic fistulas and strictures are indications for resection.

The rules

Know these

Elective colectomy: individualize, not by episode countDo not recommend elective segmental resection based on the number of episodes or age; personalize it to severity, quality of life and patient preference.

No improvement in 3–5 days: consider surgerySevere symptoms that fail to respond to nonoperative treatment within 3–5 days, or rising pain, tenderness and fever, are indications for surgery.

Uncomplicated or complicated diverticulitis?

Commonly confused

Definition	Inflamed diverticulum, no abscess, fistula, obstruction or perforation
Where to treat	Most as outpatients
Antibiotics	Selective — not routine in low-risk, immunocompetent patients
Procedure	None
Colonoscopy afterward	Only with alarm features or overdue screening

Teach & follow up

Patient education

No need to avoid nuts, seeds or popcornTo lower recurrence: high-fiber, healthy diet without avoiding nuts, seeds, corn or popcorn; physical activity; healthy weight; no smoking; and avoid routine NSAIDs and opioids.

More detail

Reference

Show 5 reference facts

The risk of complicated diverticulitis is highest at the first presentation; after nonoperative care, recurrence is about 8% at 1 year and 22% at 10 years.

CT is 95–99% sensitive for diverticulitis, but in about 10% of patients it cannot distinguish diverticulitis from colon cancer — one reason for follow-up colonoscopy.

C-reactive protein is used to guide antibiotic decisions in uncomplicated disease and to predict progression to complicated diverticulitis.

At resection, the bowel can be reanastomosed immediately in stable patients without perforation, abscess or heavy inflammation; others get a temporary colostomy with later reconstruction.

Bleeding is uncommon in diverticulitis itself; diverticular hemorrhage is covered under Lower GI Bleeding.

Pearl

Uncomplicated and well: rest, liquids, often no antibiotics. Abscess over 3–4 cm: drain it. Free air or feculent peritonitis: operate.

Sources · Merck Manual Professional — Colonic Diverticulitis (Jun 2026; cites AGA 2021, ACP 2022, ACG 2026) · Peery AF, Shaukat A, Strate LL. AGA Clinical Practice Update on Medical Management of Colonic Diverticulitis: Expert Review. Gastroenterology 2021;160:906–911 · Qaseem A et al. Diagnosis and Management of Acute Left-Sided Colonic Diverticulitis: A Clinical Guideline From the American College of Physicians. Ann Intern Med 2022;175:399–415 · Peery AF et al. ACG Clinical Guideline: Colonic Diverticulitis. Am J Gastroenterol 2026;121(7):1549–1561 (abstract via Europe PMC) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).