Acquired colonic outpouchings; inflammation produces left lower quadrant pain and fever.
Also known as: diverticulitis, diverticulosis, diverticular disease, acute diverticulitis
Overview
Diverticulosis: presence of acquired sac-like protrusions (false diverticula — lacking the muscular layer) of the colonic wall. Diverticulitis: inflammation or infection of one or more diverticula, classified as uncomplicated or complicated (abscess, fistula, obstruction, perforation).
Epidemiology
Diverticulosis prevalence rises with age: ~5% at age 40, ~30% at 60, >65% by age 85. Sigmoid colon is the most common site in Western countries (95% of cases). Right-sided diverticulosis more common in Asia. ~4% of patients with diverticulosis develop diverticulitis.
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Question 1GastrointestinalEasy
A 67-year-old male with prior diverticulitis presents with left lower quadrant pain, fever, and pneumaturia. CT shows a thickened sigmoid colon with adjacent inflammation and air in the bladder. Which of the following is the most likely complication?
ASigmoid volvulus
BColovesical fistula
CSigmoid perforation
DEnterocolic fistula
EDiverticular abscess
Reveal answer & full explanation
Correct answer: B — Colovesical fistula
ASigmoid volvulus
BColovesical fistula✓
CSigmoid perforation
DEnterocolic fistula
EDiverticular abscess
Why Colovesical fistula is correct
Pneumaturia plus fecaluria in a patient with prior diverticulitis is pathognomonic for a colovesical fistula
Colovesical fistula is the most common diverticulitis-related fistula in men (the uterus protects the bladder in women, so colovaginal is more common in women)
Air in the bladder on CT, in the absence of recent instrumentation, points directly to an enteric-vesical communication
CT with rectal or oral contrast shows the tract; cystoscopy can confirm
Treatment is surgical resection of the involved colon segment with bladder repair, often elective after inflammation cools
Why the others are wrong
Sigmoid volvulus — right-concept-wrong-mechanism; it causes a closed-loop obstruction (coffee-bean sign) with distension, not pneumaturia or bladder air
Enterocolic fistula — a colon-to-small-bowel tract is a recognized diverticular fistula but bypasses the urinary tract entirely, producing diarrhea and malabsorption rather than pneumaturia or intravesical gas
Diverticular abscess — a walled-off pericolic collection would appear as a rim-enhancing fluid collection on CT and cannot explain gas within the bladder lumen
Sigmoid perforation — tempting because fever and gas outside the colon next to an inflamed sigmoid suggest rupture, but a perforation releases gas into the peritoneal cavity or pericolic fat, causing peritonitis or a localized collection; gas within the bladder lumen with pneumaturia requires a fistulous tract into the bladder
Additional high-yield points
Recurrent urinary tract infections (UTIs) with mixed enteric organisms are a clue to the diagnosis
Question 2GastrointestinalMedium
A 65-year-old male with prior diverticulitis presents with persistent left lower quadrant pain, fever, and leukocytosis. CT shows a 5 cm pericolonic abscess adjacent to the sigmoid colon. Which of the following is the most appropriate next step in management?
AIntravenous antibiotics with serial CT imaging
BPercutaneous abscess drainage plus broad-spectrum antibiotics
CEmergent sigmoid colectomy with primary anastomosis
DOral antibiotics alone with outpatient follow-up
EUrgent colonoscopy with intravenous antibiotics
Reveal answer & full explanation
Correct answer: B — Percutaneous abscess drainage plus broad-spectrum antibiotics
AIntravenous antibiotics with serial CT imaging
BPercutaneous abscess drainage plus broad-spectrum antibiotics✓
CEmergent sigmoid colectomy with primary anastomosis
DOral antibiotics alone with outpatient follow-up
EUrgent colonoscopy with intravenous antibiotics
Why Percutaneous abscess drainage plus broad-spectrum antibiotics is correct
This patient has Hinchey stage I complicated diverticulitis (pericolonic abscess); its 5 cm size, not the Hinchey stage, is what calls for drainage
Hinchey classification: I (pericolonic abscess), II (pelvic/distant abscess), III (purulent peritonitis), IV (feculent peritonitis)
For Hinchey I–II abscesses >3–4 cm: percutaneous drainage plus IV antibiotics (ciprofloxacin/metronidazole or piperacillin-tazobactam) covering anaerobes is the standard approach
Smaller abscesses (<3–4 cm) can be treated with antibiotics alone
Why the others are wrong
Emergent sigmoid colectomy with primary anastomosis — Emergent colectomy (Hartmann procedure, or primary anastomosis with or without a diverting stoma in selected stable patients) is reserved for Hinchey III–IV (purulent or feculent peritonitis) or failed nonoperative management, not a contained abscess that can be drained
Intravenous antibiotics with serial CT imaging — Antibiotics without source control are appropriate only for abscesses smaller than 3–4 cm; a 5 cm collection is less likely to resolve on antibiotics alone, and watching it with repeat imaging prolongs sepsis and risks free perforation or fistula formation
Oral antibiotics alone with outpatient follow-up — Oral antibiotics alone are appropriate only for uncomplicated diverticulitis; small abscesses are treated with IV antibiotics, and a 5 cm abscess requires drainage
Urgent colonoscopy with intravenous antibiotics — colonoscopy is recommended after an episode of complicated diverticulitis to exclude colon cancer, but it is deferred until the acute inflammation has resolved (typically 6–8 weeks) because insufflation risks perforating the inflamed colon, and it provides no source control for a 5 cm abscess
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NSAID use (increases risk of diverticulitis, bleeding and perforation)
Sedentary lifestyle
Genetic susceptibility
Connective tissue disease (Ehlers-Danlos, Marfan — early onset)
Pathophysiology
Increased intraluminal pressure (low-fiber diet → smaller stool → segmental contraction with high pressures) drives mucosal/submucosal herniation through weak points in the muscularis where vasa recta penetrate (vasa recta erosion → diverticular bleed). Diverticulitis: micro-perforation of an obstructed diverticulum → pericolonic inflammation, potentially with abscess or free perforation.
Clinical presentation
Symptoms
Diverticulosis: usually asymptomatic; incidental on colonoscopy or imaging
Diverticular bleed: painless, brisk hematochezia (most common cause of LGIB)
Diverticulitis: left lower quadrant pain (sigmoid), constant, often worsening over 1-3 days
Fever, chills, anorexia
Change in bowel habit (constipation or diarrhea)
Nausea, vomiting (if obstruction)
Urinary symptoms (pneumaturia, fecaluria, recurrent UTI — colovesical fistula)
Signs / physical exam
LLQ tenderness ± palpable mass (phlegmon or abscess)
Low-grade fever, tachycardia
Localized peritoneal signs
Diffuse peritonitis if free perforation (Hinchey III/IV)
Rectal exam may reveal tender mass anteriorly (Douglas pouch abscess)
Classic findings
Older adult with LLQ pain, fever, and leukocytosis — 'left-sided appendicitis.'
Differential diagnosis
Acute appendicitis (especially with redundant sigmoid in LLQ or cecal diverticulitis) — Periumbilical pain migrating to RLQ; right-sided diverticulitis in Asian patients mimics this
Colorectal cancer — Older patient, weight loss, anemia, change in bowel habit; colonoscopy 6-8 wk after recovery from complicated diverticulitis, or after uncomplicated disease with alarm features or if not current on screening
Gynecologic: ovarian torsion, PID, ectopic pregnancy — Pelvic exam, pregnancy test, pelvic ultrasound in women
Epiploic appendagitis — Localized LLQ pain, characteristic small fat-density CT lesion adjacent to colon; self-limited
Diagnostic workup
Diagnostic criteria
CT-confirmed pericolonic inflammation with diverticula. Modified Hinchey classification: Ia (pericolic phlegmon), Ib (pericolic abscess), II (pelvic/intra-abdominal abscess), III (purulent peritonitis), IV (feculent peritonitis).
Labs
CBC (leukocytosis with left shift)
BMP, lactate (if severe)
CRP — predicts severity
Urinalysis (exclude UTI, identify fistula)
Urine pregnancy test in women of childbearing age
Blood cultures if septic
Imaging
CT abdomen/pelvis with IV contrast — MODALITY OF CHOICE; identifies pericolic inflammation, bowel wall thickening, abscess, fistula, free air; classifies by Hinchey stage
AVOID colonoscopy during acute diverticulitis (perforation risk); perform 6-8 weeks AFTER recovery from complicated diverticulitis to exclude malignancy; after uncomplicated disease, only with alarm features or if not current on colorectal cancer screening (ACG 2026)
Ultrasound or MRI in pregnancy or young patients to limit radiation
Diagnostic algorithm
Hinchey Stage
CT Finding
Management
Ia
Pericolic phlegmon, no abscess
Supportive care, no routine antibiotics if low-risk (antibiotics if high-risk); usually outpatient
Ib
Pericolic abscess
IV antibiotics ± percutaneous drainage if ≥3-4 cm
II
Pelvic or intra-abdominal abscess
Percutaneous drainage + IV antibiotics
III
Purulent peritonitis
Emergent surgery (Hartmann or resection + anastomosis with diversion)
IV
Feculent peritonitis
Emergent surgery
Modified Hinchey classification of acute diverticulitis and stage-directed management.
Treatment
First-line
Uncomplicated diverticulitis (Hinchey 0/Ia: no abscess, perforation, fistula, or obstruction): often managed as outpatient with supportive care and diet as tolerated (no routine bowel rest); antibiotics selective rather than universal per ACG 2026 (give for high-risk features, immunocompromise, frailty, or inability to ensure safe outpatient management)
Outpatient antibiotic regimens: amoxicillin-clavulanate, or ciprofloxacin/levofloxacin + metronidazole × 7-10 days
Clear liquid diet advanced as tolerated
Follow-up in 2-3 days
Inpatient — moderate diverticulitis
Admit if unable to tolerate PO, significant comorbidities, immunocompromise, failed outpatient management, abscess, or peritoneal signs
IV antibiotics: piperacillin-tazobactam, ceftriaxone + metronidazole, or ertapenem
Bowel rest, IV fluids, analgesia (avoid NSAIDs)
Transition to oral antibiotics with clinical improvement
Abscess (Hinchey Ib-II)
Abscess <3-4 cm: IV antibiotics alone
Abscess ≥3-4 cm: percutaneous (image-guided) drainage + IV antibiotics
Surgery if failure of drainage or clinical deterioration
Perforation with peritonitis (Hinchey III/IV)
Emergent surgery — Hartmann procedure (sigmoid resection with end colostomy) or primary anastomosis with diverting ileostomy
Laparoscopic lavage controversial; not preferred over resection
Broad-spectrum IV antibiotics
Recurrent or complicated disease
Elective sigmoid resection — individualized; consider after recurrent episodes (no longer routine after 2nd episode), persistent symptoms, complicated disease (fistula, stricture), immunocompromise
AGA 2021 Clinical Practice Update and ACG 2026: individualized shared decision-making (quality of life, complicated disease, immunocompromise) rather than a number-of-episodes rule
Diverticular bleed
Resuscitate; most stop spontaneously (75%)
Colonoscopy with hemostasis (clip, epinephrine, thermal) for active bleeding source
CT angiography or tagged RBC scan if hemodynamically stable but ongoing bleeding
IR angiographic embolization for refractory or massive bleed
Surgery for failed embolization and persistent hemodynamic instability
After a bleed: stop non-aspirin NSAIDs and aspirin taken only for primary prevention, continue aspirin for established cardiovascular disease, and encourage a high-fiber diet; consider elective resection for recurrent bleeding from the same segment
Complications
Abscess (intra-abdominal, pelvic)
Fistula — colovesical (most common, M:F due to uterus barrier), colovaginal, coloenteric, colocutaneous
Stricture and partial obstruction
Free perforation with peritonitis
Diverticular hemorrhage — most common cause of brisk lower GI bleeding
Recurrence (15-30% within 5 yr after first episode)
PANCE pearls
AVOID colonoscopy during acute diverticulitis — perforation risk. Schedule 6-8 weeks after recovery from complicated diverticulitis to exclude underlying malignancy; after uncomplicated disease, only with alarm features or if not current on colorectal cancer screening (ACG 2026).
Antibiotics are no longer routine for uncomplicated diverticulitis in low-risk patients (AGA 2015; ACG 2026) — observation with close follow-up is acceptable.
Pneumaturia, fecaluria, or recurrent polymicrobial UTI in older adult = colovesical fistula until proven otherwise.
Right-sided diverticulitis is more common in Asian populations and frequently misdiagnosed as appendicitis.
Old teaching to avoid nuts, seeds, and popcorn has NO evidence supporting it (Strate, JAMA 2008).
Elective surgery decision is individualized — not by episode count. Consider in young immunocompromised patients, persistent symptoms, complicated disease.
Smoldering/chronic diverticulitis (low-grade inflammation without abscess) may benefit from elective resection.
References
AGA 2015 — Stollman N et al. AGA Institute Guideline on the Management of Acute Diverticulitis. Gastroenterology 2015;149:1944-1949
ASCRS 2020 — Hall J et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Treatment of Left-Sided Colonic Diverticulitis. Dis Colon Rectum 2020;63:728-747
Strate Nuts/Seeds — Strate LL et al. Nut, Corn, and Popcorn Consumption and the Incidence of Diverticular Disease. JAMA 2008;300:907-914
AGA 2021 CPU — Peery AF, Shaukat A, Strate LL. AGA Clinical Practice Update on Medical Management of Colonic Diverticulitis: Expert Review. Gastroenterology 2021;160:906-911
ACG 2026 — Peery AF et al. ACG Clinical Guideline: Colonic Diverticulitis. Am J Gastroenterol 2026;121:1549-1561
ACG LGIB 2023 — Sengupta N et al. Management of Patients With Acute Lower Gastrointestinal Bleeding: An Updated ACG Guideline. Am J Gastroenterol 2023;118:208-231
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