Diverticular Disease & Lower GI Bleeding
A high-yield Step 2 CK lesson contrasting painless diverticular bleeding with painful diverticulitis — pathophysiology, presentation, CT-first diagnosis, and next-best-step management, including the antibiotic-selective shift for uncomplicated disease, Hinchey-guided surgery, and the lower-GI-bleed workup algorithm.
Pathophysiology: one pouch, two very different complications
Diverticula are outpouchings of colonic mucosa and submucosa that herniate through the muscularis propria at the weak points where the vasa recta penetrate the bowel wall — so they are false (pseudo)diverticula (a true diverticulum such as Meckel's contains all layers). They cluster in the sigmoid colon, which has the smallest radius and therefore — by Laplace's law — the highest intraluminal pressures; a chronic low-fiber diet, constipation, and aging drive their formation. Most people have asymptomatic diverticulosis found incidentally.
Two very different complications arise, and Step 2 hinges on separating them:
- A diverticulum can bleed when the vasa recta draped over its dome ruptures → painless, brisk hematochezia.
- Or it can become inflamed/microperforated (classically when stool obstructs its neck) → diverticulitis — pain + fever, rarely bleeds.
Classic pearl: brisk bleeding and acute diverticulitis almost never occur together.
- Pseudodiverticula = only mucosa + submucosa herniate (vs. all-layer true diverticula)
- Sigmoid = most common location overall; right-sided diverticula have the greatest propensity to bleed
- Diverticulosis is the #1 cause of acute lower GI bleeding (LGIB) in adults; angiodysplasia is the next most common
- Diverticular bleed = painless, large-volume hematochezia; stops spontaneously in ~75%
- Diverticulitis = LLQ pain + fever + leukocytosis ('left-sided appendicitis'); rarely bleeds
- CT abdomen/pelvis with IV contrast = test of choice for suspected diverticulitis
- Colonoscopy is contraindicated in acute diverticulitis (perforation risk) — do it 6–8 weeks after recovery to exclude colorectal cancer
- Risk factors: low fiber (classic), obesity, smoking, and NSAIDs/aspirin (raise bleeding and perforation risk)
Diverticular bleeding vs. acute diverticulitis
| Feature | Diverticular bleeding | Acute diverticulitis |
|---|---|---|
| Mechanism | Rupture of vasa recta over the dome | Stool obstructs neck → micro-perforation/inflammation |
| Pain | Painless | LLQ pain, tender |
| Bleeding | Brisk, painless hematochezia | Usually none |
| Fever / WBC | Absent | Fever + leukocytosis |
| Location bias | Right colon bleeds more | Sigmoid (left) |
| Best test | Colonoscopy after prep (CTA if unstable) | CT with IV contrast |
| Colonoscopy timing | Diagnostic + therapeutic once stable/prepped | Contraindicated acutely; do at 6–8 wks |
| First move | Resuscitate; most self-limited | Bowel rest ± selective antibiotics |
A 62-year-old man has 2 days of left-lower-quadrant pain, low-grade fever, and constipation. Exam: LLQ tenderness, no rebound. WBC 14,000.
Diagnosis: acute (uncomplicated) sigmoid diverticulitis.
Next best step: CT abdomen/pelvis with IV (± oral) contrast — confirms and stages disease (wall thickening, pericolic fat stranding, diverticula; look for abscess or free air).
Management:
- Uncomplicated + immunocompetent → outpatient; clear-liquid diet. Per AGA/ACP, antibiotics are used selectively (many mild cases resolve without them); if given → amoxicillin-clavulanate, or cipro + metronidazole.
- Abscess ≥3–4 cm → CT-guided percutaneous drainage + IV antibiotics.
- Free air / diffuse peritonitis → emergent surgery (Hartmann's).
- Do NOT scope now — colonoscopy at 6–8 weeks to exclude malignancy.
A 78-year-old woman on aspirin has sudden painless passage of maroon/bright-red stool and lightheadedness. BP 118/70, HR 96, no abdominal pain.
Diagnosis: likely diverticular LGIB (painless hematochezia in an older adult).
Next best steps:
- Resuscitate first — 2 large-bore IVs, crystalloid, type & cross, CBC/coags.
- If hemodynamically unstable or bleeding briskly → first exclude a rapid upper GI source (≈10–15% of hematochezia is brisk UGIB) with EGD — a negative NG aspirate does not rule it out.
- Once stable and bowel-prepped → colonoscopy is first-line (diagnostic and therapeutic: clips, thermal coagulation, epinephrine).
- Ongoing/massive bleed that colonoscopy can't localize → CT angiography → catheter angiography with embolization; a tagged-RBC scan can localize slower bleeds (~0.1–0.4 mL/min).
- Segmental colectomy = last resort for uncontrolled bleeding.
- Uncomplicated (immunocompetent): clear liquids; selective antibiotics — routine antibiotics no longer mandatory for mild cases (ACP 2022 / AGA 2015)
- Complicated = abscess, perforation, obstruction, or fistula → admit + IV antibiotics covering gram-negatives + anaerobes
- Abscess <3–4 cm → IV antibiotics alone; ≥3–4 cm → percutaneous drainage
- Hinchey: I pericolic abscess · II pelvic/distant abscess · III purulent peritonitis · IV feculent peritonitis
- Hinchey III–IV / free air / peritonitis → emergent surgery — Hartmann's (sigmoidectomy + end colostomy + oversewn rectal stump)
- Colovesical fistula (pneumaturia, fecaluria, recurrent polymicrobial UTIs) = classic complication, more common in men
- Elective sigmoid resection is individualized (not by episode count), done after inflammation resolves
Differential: common causes of lower GI bleeding
| Cause | Classic clue | Key association |
|---|---|---|
| Diverticulosis | Painless, brisk hematochezia, older adult | Right colon bleeds most |
| Angiodysplasia | Painless, recurrent/occult bleeding | Aortic stenosis (Heyde), ESRD, vWD; right colon |
| Ischemic colitis | Crampy abdominal pain + bloody diarrhea | Watershed (splenic flexure); post-AAA repair; thumbprinting |
| Colorectal cancer | Occult blood, iron-deficiency anemia, weight loss | Change in stool caliber |
| Hemorrhoids / anorectal | Bright-red blood coating stool or on paper | Small-volume, painless (internal) |
| IBD / infectious colitis | Bloody diarrhea + pain, younger patient | Systemic/inflammatory signs |
A clean way to keep the two diverticular complications straight:
- Divertic-OSIS → BLEEDS: painless hematochezia, no fever → resuscitate, then colonoscopy to localize/treat.
- Divertic-ITIS → HURTS: LLQ pain + fever + high WBC → CT with IV contrast to diagnose; colonoscopy is contraindicated acutely (scope at 6–8 wks).
Also remember "left-sided appendicitis" for diverticulitis — same syndrome (localized pain, fever, leukocytosis), opposite side of the abdomen.
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