Diverticulitis

Inflammation or infection of colonic diverticula — most commonly sigmoid colon

Symptoms / Associated Sx

  • LLQ pain (acute onset, constant) — "left-sided appendicitis"

  • Fever, chills, nausea, vomiting, anorexia

  • Change in bowel habits (constipation or diarrhea)

  • LLQ tenderness ± guarding on exam

Denies

  • Free air or peritoneal signs (rules out perforation if absent)

  • Feculent or pneumaturia (rules out colovesical fistula if absent)

  • RLQ pain with periumbilical migration (rules out appendicitis)

  • Rectal bleeding (distinguishes from diverticular bleed or ischemic colitis)

Social History (SHx)

Low-fiber diet, obesity, inactivity, NSAID/steroid use (perforation risk), prior diverticulitis, alcohol, smoking.

Main Etiology

  • Microperforation of colonic diverticulum → pericolonic inflammation/infection

  • Most common organisms: E. coli, Bacteroides fragilis, Klebsiella

  • Low-fiber, high-fat diet → increased intraluminal pressure

Most Common DDx

  • Colon cancer (CT may be indistinguishable from diverticulitis — mass vs. phlegmon; colonoscopy at 4–6 weeks post-resolution mandatory to exclude malignancy)

  • Appendicitis (RLQ pain + migration from periumbilical; rebound at McBurney's; CT shows appendix inflammation; no diverticular changes)

  • Ischemic colitis (LLQ or diffuse pain; elderly with vascular disease; bloody diarrhea; CT shows bowel wall thickening without pericolic stranding typical of diverticulitis; colonoscopy shows mucosal ischemia)

  • IBD flare (younger patient; known IBD history; colonoscopy and biopsy distinguish; skip lesions or rectal involvement)

  • Ovarian pathology — torsion, abscess, cyst rupture in women (LLQ pain; pelvic US shows ovarian abnormality; no diverticulosis)

  • Left-sided nephrolithiasis (colicky flank-to-groin pain; hematuria; CT shows ureteral stone; no bowel wall changes)

  • Sigmoid volvulus (massive distension + obstipation; "coffee bean" on AXR; colonoscopic decompression is treatment)

DATA

  • CBC (WBC >12k); CMP, CRP, lactate; UA

  • CT abdomen/pelvis with IV contrast (gold standard — Hinchey classification)

  • Colonoscopy: NOT during acute episode; schedule 4–6 weeks post-resolution

Home Meds

  • NSAIDs (hold — perforation risk); corticosteroids (hold); anticoagulants (hold if surgery anticipated)

Plan

  • Uncomplicated (Hinchey Ia — no abscess):

    • Outpatient if tolerating PO: Ciprofloxacin 500 mg PO BID + Metronidazole 500 mg PO TID × 7–10 days OR Amoxicillin-clavulanate 875 mg PO BID × 7–10 days

    • Clear liquid diet → low-fiber → high-fiber at 4–6 weeks

  • Complicated (Hinchey Ib–II — abscess) — inpatient:

    • NPO; IV fluids; Piperacillin-tazobactam 3.375 g IV q6h (or cefoxitin 2 g IV q6–8h)

    • Abscess ≥3–4 cm: CT-guided percutaneous drainage + antibiotics

    • Step-down PO when improving: Cipro 500 mg BID + Metronidazole 500 mg TID × 7–14 days total

  • Perforated (Hinchey III–IV) — emergent surgery:

    • Hartmann's procedure or primary anastomosis + diverting ileostomy

    • Meropenem 1 g IV q8h ± Vancomycin if hemodynamically unstable

  • Colonoscopy 4–6 weeks post-resolution (rule out malignancy); daily CBC, CMP; trend fever curve

  • Surgery consult for complicated disease; GI consult for colonoscopy planning; PT/OT if prolonged

  • Discharge: Complete antibiotic course; high-fiber diet (25–35 g/day) after recovery; avoid NSAIDs; colonoscopy at 4–6 weeks; elective sigmoid resection discussion for ≥2 episodes or young/immunocompromised; surgery/GI follow-up 2–4 weeks

Red Flags

  • Free air on CT → perforated diverticulitis → emergent surgery

  • Hinchey III–IV (purulent or feculent peritonitis) → emergent Hartmann's

  • Colovesical fistula (feculent urine, pneumaturia) → surgical correction

  • No improvement after 48–72h IV antibiotics → repeat CT (new abscess, treatment failure)

  • Immunocompromised + diverticulitis → higher perforation risk; lower threshold for admission and surgery

Senior IM Resident Pearls

  • Hinchey classification: Ia = pericolic phlegmon; Ib = pericolic/mesenteric abscess; II = pelvic abscess; III = purulent peritonitis; IV = feculent peritonitis

  • AVOD/DIABOLO trials: Non-inferior outcomes without antibiotics in uncomplicated diverticulitis in select patients — discuss with attending; still commonly treated in U.S.

  • Colonoscopy mandatory 4–6 weeks post-resolution — colon cancer found in ~1.6% of post-diverticulitis colonoscopies; CT cannot distinguish

  • Common mistake: Colonoscopy during acute episode — contraindicated (perforation risk)