Gastrointestinal

Diverticulitis: outpatient vs inpatient management

Clinical Overview and When to Suspect Diverticulitis

— Uncomplicated (~75%): localized inflammation, no abscess/perforation/fistula/obstruction

— Complicated (~25%): abscess, free perforation, fistula (colovesical most common), obstruction, or stricture

— Classified by modified Hinchey: Ia (phlegmon), Ib (pericolic abscess <4 cm), II (pelvic/distant abscess), III (purulent peritonitis), IV (feculent peritonitis)

— Adult ≥40 (peak 50–70) with LLQ pain, low-grade fever, change in bowel habits, mild leukocytosis

— Prior episode of diverticulitis or known diverticulosis on prior colonoscopy

— Risk factors: obesity, low-fiber/high-red-meat diet, smoking, NSAID/opioid use, sedentary lifestyle, chronic steroids/immunosuppression

— Outpatient candidates: uncomplicated disease, tolerates PO, no significant comorbidity, no immunosuppression, reliable, can return if worsening, no high fever or sepsis physiology

— Inpatient: complicated disease (abscess, perforation, obstruction, fistula), sepsis, peritonitis, intolerance of PO, immunocompromise (transplant, chemo, chronic steroids, advanced CKD), failure of outpatient therapy, pregnancy, frailty/poor social support

Definition: Acute inflammation/infection of colonic diverticula, most often involving the sigmoid colon in Western populations (right-sided more common in Asian patients). Pathophysiology involves micro-perforation of a diverticulum with localized peridiverticular inflammation, not simple "infection" of stool-filled pouches.

Spectrum of disease:

When to suspect on Step 3:

Outpatient vs inpatient framing (the core Step 3 decision):

Step 3 management: Don't reflexively admit every diverticulitis. The pivotal triage point is CT findings + ability to take PO + host factors, not pain severity alone.

Board pearl: Acute diverticulitis is not diagnosed or evaluated with colonoscopy in the acute setting — risk of perforation. Colonoscopy is deferred 6–8 weeks after resolution to exclude underlying malignancy if not done recently.

Presentation Patterns and Key History

— Gradual onset, steady, localized to LLQ ("left-sided appendicitis")

— May radiate to suprapubic area, left flank, or back

— Worse with movement if peritoneal irritation present

— Sudden severe diffuse pain suggests free perforation — admit, surgery consult

— Nausea ± vomiting (vomiting more prominent suggests obstruction or ileus)

— Constipation > diarrhea; tenesmus if rectal involvement

— Hematochezia is uncommon in diverticulitis — bleeding usually points to diverticular bleeding (a distinct, painless entity) or alternative diagnosis

— Pneumaturia/fecaluria/recurrent polymicrobial UTI → colovesical fistula (most common; men > women because uterus shields bladder in women)

— Vaginal passage of stool/gas → colovaginal fistula (typically post-hysterectomy women)

— Feculent skin drainage → colocutaneous fistula

— Prior episodes and their severity/treatment (predicts recurrence and surgical candidacy)

— Immunosuppression: solid-organ transplant, chronic prednisone ≥20 mg, biologics, active chemotherapy, advanced HIV — these patients underexpress symptoms and present late

— NSAID, opioid, and steroid use — increase perforation risk

— Pregnancy status (rare but reported)

— Last colonoscopy date

Classic stem: 55-year-old with constant LLQ abdominal pain for 2–3 days, low-grade fever, nausea, mild anorexia, and altered bowel habits (constipation more common than diarrhea, but either possible).

Pain characteristics:

GI symptoms:

Fistula clues (history-driven):

Key historical risk modifiers:

Key distinction: Diverticulosis (asymptomatic outpouchings, may bleed painlessly) vs diverticulitis (inflamed/perforated, painful, rarely bleeds). Step 3 stems exploit this: painless brisk hematochezia in an older adult = diverticular bleed, not diverticulitis — workup is colonoscopy ± CTA, not antibiotics.

Board pearl: In immunosuppressed patients, absence of fever or leukocytosis does not rule out complicated diverticulitis. Have a low threshold for CT and admission.

Physical Exam Findings (and Hemodynamic Assessment)

— Uncomplicated: well-appearing, low-grade fever (<38.5°C), HR <100, normotensive, tolerating sips

— Complicated/sepsis: T >38.5°C or <36°C, HR >100, RR >22, hypotension, altered mentation

— qSOFA ≥2 or SIRS criteria + suspected source → sepsis pathway: lactate, blood cultures, IV fluids, broad antibiotics, admit

— LLQ tenderness is the hallmark; may have palpable tender mass (phlegmon or abscess)

— Voluntary guarding common in uncomplicated; involuntary guarding, rigidity, rebound → peritonitis → urgent surgical evaluation

— Distension and tympany → obstruction or ileus

— Hypoactive/absent bowel sounds in advanced disease

— Tenderness anteriorly or palpable boggy mass → low pelvic abscess (consider transrectal drainage)

— Gross blood is atypical for diverticulitis — reconsider diagnosis (IBD, ischemic colitis, malignancy, diverticular bleed)

— SBP <90 or MAP <65 → 30 mL/kg crystalloid bolus, lactate, cultures, IV broad-spectrum antibiotics within 1 hour, ICU consideration

— Persistent tachycardia after fluids in a "stable-looking" patient = early complicated disease until proven otherwise

General appearance and vitals (drives triage):

Abdominal exam:

Rectal exam:

Pelvic exam (women): Essential to exclude tubo-ovarian abscess, PID, ovarian torsion, ectopic in reproductive-age women with LLQ pain.

Genitourinary: CVA tenderness suggests pyelonephritis or ureteral involvement from adjacent inflammation; suprapubic tenderness with pneumaturia hints at colovesical fistula.

Skin/extremities: Look for signs of chronic immunosuppression (cushingoid features, transplant scars) that shift you toward inpatient management.

Hemodynamic action thresholds:

CCS pearl: On a CCS case, always order vitals, abdominal exam, rectal exam, and (when relevant) pelvic exam before locking in imaging. Missing the rectal/pelvic step is a frequent CCS deduction in LLQ pain cases.

Diagnostic Workup — Initial Labs and Imaging

— CBC with differential: leukocytosis with left shift typical; normal WBC does not exclude diverticulitis, especially in immunosuppressed

— BMP: assess hydration, AKI, electrolytes (vomiting/poor intake)

— CRP: >50 mg/L correlates with complicated disease and helps risk-stratify ambiguous cases

— Lactate: if SIRS/sepsis features, suspected ischemia, or peritonitis

— LFTs and lipase: broaden differential (cholecystitis, pancreatitis), especially if atypical pain location

— Urinalysis: rule out UTI/stone; pyuria + fecaluria + polymicrobial growth is the classic colovesical fistula triad

— Beta-hCG in any reproductive-age woman before imaging

— Type and screen, coags if surgery or drainage anticipated

— Blood cultures ×2 if febrile, septic, or immunocompromised

— Sensitivity/specificity ~95%; defines Hinchey stage and directs management

— Findings: pericolic fat stranding, bowel wall thickening (>4 mm), diverticula, phlegmon, abscess (size critical: <4 cm vs ≥4 cm), extraluminal air, free fluid, fistula tract

— IV contrast is preferred; oral contrast optional and often omitted in modern protocols

— Avoid iodinated IV contrast only in severe contrast allergy or AKI without dialysis access — substitute MRI or non-contrast CT

— MRI abdomen/pelvis: pregnant patients, young patients to avoid radiation if recurrent imaging anticipated

— Graded-compression US: operator-dependent; reasonable in pregnancy or pediatrics

— Plain films: only to screen for free air or obstruction when CT unavailable — limited yield

Core labs (order on every suspected case):

Imaging — CT abdomen/pelvis with IV (± oral) contrast is the gold standard:

Alternative imaging:

Avoid in acute phase: colonoscopy, sigmoidoscopy, barium enema — perforation risk.

Step 3 management: Do not skip CT even if exam seems classic — CT is what differentiates outpatient-eligible uncomplicated disease from complicated disease requiring admission, drainage, or surgery. This single decision drives the entire disposition.

Board pearl: A first episode of "clinical diverticulitis" without prior imaging confirmation should always be confirmed on CT to avoid missing colon cancer, ischemic colitis, or appendicitis masquerading as diverticulitis.

Diagnostic Workup — Advanced and Confirmatory Studies

— Indicated 6–8 weeks after resolution of a first episode of complicated diverticulitis, or any episode if colonoscopy not performed within prior 1 year per most US guidelines (ASCRS, ACG)

— Rationale: colon cancer mimics complicated diverticulitis on CT in ~1–2% of cases; perforated cancers can present identically

— May be omitted if a high-quality recent colonoscopy is documented and disease was clearly uncomplicated

— Indicated for abscess ≥4 cm (some centers ≥3 cm) that is accessible

— Allows source control without emergent surgery; converts urgent operation to elective interval resection (if needed)

— Smaller abscesses (<3–4 cm) often resolve with IV antibiotics alone

— Hemodynamically stable: colonoscopy after rapid prep

— Brisk active bleeding, unstable: CT angiography first → IR embolization; tagged RBC scan if intermittent

— This is not the diverticulitis pathway — it's the diverticular bleed pathway. Step 3 stems test that you don't conflate them.

Interval colonoscopy (post-acute):

CT-guided percutaneous drainage:

Cystoscopy and cystography: Confirm and characterize colovesical fistula when CT shows air in the bladder without prior instrumentation. CT with rectal contrast or MRI can also map fistulas.

Contrast enema (water-soluble, e.g., gastrografin): Useful weeks after the acute episode to evaluate for stricture or fistula before elective surgery; never barium in acute setting.

Lower GI bleeding workup (if hematochezia dominates):

Biomarker nuance: Procalcitonin is not routinely required but may support sepsis assessment in ambiguous immunocompromised cases.

Pregnancy workup adjustment: MRI abdomen/pelvis without gadolinium is preferred confirmatory test after ultrasound; obstetric co-management is standard.

Key distinction: Drainage (IR, percutaneous) treats abscess; resection treats recurrent or complicated disease electively. Emergent surgery (Hartmann's or primary anastomosis with diversion) is reserved for Hinchey III/IV, hemodynamic instability, or failed drainage.

Board pearl: Always document smoking status, immunosuppression, and prior episodes — these change whether you offer elective sigmoid colectomy after recovery.

Risk Stratification — Outpatient vs Inpatient Triage

— CT confirms uncomplicated diverticulitis (no abscess, perforation, fistula, obstruction)

— Patient tolerates oral intake (fluids and meds)

— Hemodynamically stable, T <38.5°C, no peritonitis

— Not significantly immunocompromised (no transplant, no chronic high-dose steroids, no active chemo, controlled chronic conditions)

— Adequate social support and ability to return promptly if worse

— Reliable follow-up within 48–72 hours

— No pregnancy, no severe comorbidity (advanced CHF, decompensated cirrhosis, ESRD)

— Complicated disease on CT (abscess, free air, peritonitis, obstruction, fistula)

— Sepsis, SIRS, peritonitis on exam

— Intolerance of PO or persistent vomiting

— Immunosuppression

— Failed outpatient therapy at 48–72 h

— Severe comorbidity, frailty, advanced age with poor reserve

— Pregnancy

— Uncontrolled pain requiring parenteral analgesia

— Inability to follow up or unreliable home situation

— Antibiotics are now optional in highly selected immunocompetent outpatients with mild, uncomplicated CT-confirmed diverticulitis (AVOD, DIABOLO trials showed no benefit of routine antibiotics in this narrow group)

— On Step 3, the safer default is still to treat with antibiotics, especially if any uncertainty, comorbidity, immunosuppression, or elevated CRP/WBC

The pivotal Step 3 decision tree in acute diverticulitis:

Outpatient management is appropriate when ALL of the following are true:

Inpatient admission criteria (any one suffices):

ICU triage: Septic shock, peritonitis with hemodynamic instability, Hinchey III/IV → ICU + emergent surgical consult.

Recent evidence shift (AGA/ASCRS):

Step 3 management: Use a structured checklist — CT severity, vitals, PO tolerance, host status, social factors. If any single inpatient criterion is met, admit. Outpatient management requires meeting all outpatient criteria.

Board pearl: An "immunocompromised" patient with even mild CT findings should generally be admitted — they progress fast and present late. This is one of the most testable single-line rules on Step 3.

Pharmacotherapy — First-Line Antibiotic Regimens

— Cover gram-negative enterics (E. coli, Klebsiella) and anaerobes (Bacteroides fragilis)

— Duration: 4–7 days for uncomplicated disease (shorter courses, e.g., 4 days, supported by recent data); 10–14 days for complicated disease with abscess

— Reassess at 48–72 hours; lack of improvement triggers re-imaging

— Ciprofloxacin 500 mg BID + metronidazole 500 mg TID × 4–7 days (classic regimen)

— Amoxicillin-clavulanate 875/125 mg BID × 4–7 days (preferred when fluoroquinolone avoidance desired — tendinopathy, aortic aneurysm risk, QT prolongation, elderly fall risk)

— TMP-SMX DS BID + metronidazole as alternative

— Avoid fluoroquinolones in pregnancy, children, and patients on QT-prolonging meds or with known aortic disease

— Ceftriaxone 1–2 g IV daily + metronidazole 500 mg IV q8h (standard, narrow, cost-effective)

— Piperacillin-tazobactam 3.375 g IV q6h for severe disease, sepsis, healthcare-associated, or recent antibiotic exposure

— Ertapenem 1 g IV daily as single-agent alternative

— Carbapenem (meropenem, imipenem) reserved for septic shock, ESBL risk, or prior multidrug-resistant organisms

— Penicillin allergy (severe): ciprofloxacin/levofloxacin + metronidazole or aztreonam + metronidazole

— IV fluids for resuscitation; transition to PO once tolerating

— Avoid NSAIDs and opioids when possible — NSAIDs increase perforation; opioids worsen ileus and may mask exam. Acetaminophen first-line; antispasmodics situational

— Antiemetics (ondansetron) as needed

— VTE prophylaxis for admitted patients

— Bowel rest: clear liquids, advance as tolerated; NPO only if obstruction, ileus, or planned procedure

General principles:

Outpatient PO regimens (uncomplicated):

Inpatient IV regimens (complicated or unable to tolerate PO):

Adjuncts:

Step 3 management: Always specify duration in your discharge orders and arrange 48–72 h phone or in-person reassessment. Failure to improve = re-image with CT, not just extend antibiotics.

Board pearl: Fluoroquinolone + metronidazole remains the most-tested outpatient regimen, but Amox-Clav is increasingly favored — know both.

Procedures and Surgical Management

— Indication: abscess ≥3–4 cm, accessible on imaging

— Performed by IR; leaves drain in place until output minimal and clinical improvement

— Allows conversion of urgent surgery to interval, elective, single-stage resection

— Repeat CT if persistent fever or leukocytosis despite drain

— Hinchey III (purulent peritonitis) or Hinchey IV (feculent peritonitis)

— Free perforation with peritonitis

— Sepsis/hemodynamic instability not responding to resuscitation

— Failed percutaneous drainage

— Obstruction not relieved conservatively

— Uncontrolled hemorrhage (rare in diverticulitis itself)

— Hartmann procedure: sigmoid resection + end colostomy + rectal stump — preferred for unstable patients, feculent peritonitis; staged reversal in 3–6 months (reversal carries 10–20% morbidity, ~50% never reversed in frail patients)

— Primary anastomosis ± diverting loop ileostomy: appropriate for stable patients with purulent (not feculent) peritonitis; lower long-term morbidity, fewer never-reversed stomas

— Laparoscopic lavage: historically tried for Hinchey III but largely abandoned due to higher reintervention rates

— Complicated disease (abscess, fistula, stricture, obstruction) once recovered

— Persistent or recurrent symptoms impacting quality of life

— Immunocompromised patients with even a single complicated episode

— Inability to exclude malignancy

— Old rule of "≥2 episodes → surgery" is obsolete — decision is now individualized

Percutaneous CT-guided drainage:

Emergent surgery — indications:

Operative options:

Elective sigmoid colectomy — indications (individualized, not by episode count alone):

Fistula management: Elective single-stage resection of involved colon with primary repair of bladder/vagina/skin defect; preoperative workup includes cystoscopy and contrast studies.

Stricture management: Endoscopic dilation rarely sufficient; elective resection usually required.

CCS pearl: On a CCS case of peritonitis, the correct sequence is IV access → fluids → broad-spectrum antibiotics → lactate/cultures → urgent surgery consult → CT only if stable enough. Do not delay surgical consult while waiting for imaging in an unstable patient.

Board pearl: Hartmann = unstable/feculent; primary anastomosis = stable/purulent. Memorize this dichotomy.

Special Populations — Elderly and Renal/Hepatic Impairment

— Atypical presentations: minimal pain, no fever, only mild anorexia or confusion

— Lower threshold for CT and admission; physiologic reserve is limited

— Polypharmacy: NSAIDs, anticoagulants, antiplatelets, opioids each modify risk and management

— Frailty (Clinical Frailty Scale) better predicts surgical outcomes than age alone

— Discuss goals of care early, especially before emergency surgery — Hartmann in a frail 85-year-old carries 30-day mortality up to 20–30%

— Avoid fluoroquinolones when possible (tendinopathy, falls, QT, delirium); Amox-Clav preferred

— Dose-adjust ciprofloxacin, levofloxacin, TMP-SMX, piperacillin-tazobactam, ertapenem, meropenem per CrCl

— Metronidazole and ceftriaxone generally do not require renal dose adjustment for standard durations

— Avoid IV iodinated contrast in eGFR <30 unless benefit outweighs risk; MRI alternative if available

— Watch for AKI from sepsis, NSAIDs, dehydration — hold nephrotoxins, ensure euvolemia

— Higher perforation, mortality, and post-op morbidity

— Spontaneous bacterial peritonitis is a competing diagnosis — paracentesis if ascites

— Metronidazole accumulates in severe hepatic dysfunction → reduce dose or interval; consider alternative anaerobic coverage

— Coagulopathy increases bleeding risk during drainage/surgery — correct INR, platelets cautiously

— CHF: cautious fluid resuscitation; balance sepsis volume targets against pulmonary edema

— COPD/OSA: optimize before any surgical intervention; perioperative pulmonary toilet

— Hyperglycemia worsens infection; target glucose 140–180 mg/dL inpatient

— Hold metformin around contrast/sepsis; resume when stable and renal function normal

Elderly patients (≥65, especially ≥75):

Renal impairment:

Hepatic impairment / cirrhosis:

Cardiopulmonary comorbidity:

Diabetes:

Step 3 management: In elderly or immunocompromised patients with diverticulitis, default to admission, narrow-spectrum IV antibiotics, early surgical consult, and explicit goals-of-care conversation before complications force the discussion.

Board pearl: A frail elderly patient with "mild diverticulitis" who looks deceptively well on initial exam can crash within hours — repeat vitals and exams q4–6h are mandatory.

Special Populations — Pregnancy, Young Adults, Immunocompromised

— Rare but reported; sigmoid is displaced upward by gravid uterus, so pain may localize atypically

— First-line imaging: graded-compression ultrasound → MRI abdomen/pelvis without gadolinium if inconclusive; CT only if MRI unavailable and benefit outweighs risk

— Antibiotics: avoid fluoroquinolones and metronidazole in 1st trimester (controversial; many obstetricians use metronidazole after 1st trimester if needed); ceftriaxone is safe across pregnancy; amoxicillin-clavulanate is acceptable

— Multidisciplinary care with OB; admit for any uncertainty

— Surgery, when needed, is best in 2nd trimester; emergent surgery proceeds regardless of trimester

— Historically thought to have more aggressive disease — recent data suggest similar natural history but more cumulative recurrences over a lifetime

— Don't anchor to "too young for diverticulitis" — obesity, low fiber, and family history increase risk

— Always confirm with CT and arrange interval colonoscopy to exclude malignancy or IBD

— Surgical thresholds individualized, not age-driven

— Blunted symptoms, delayed presentation, higher perforation rate

— Admit all suspected cases; low threshold for CT regardless of exam

— Broad-spectrum IV antibiotics (piperacillin-tazobactam) and early surgical consult

— Lower threshold for elective resection after a single complicated episode because recurrence is poorly tolerated

— Consider stress-dose steroids perioperatively for chronic steroid users

— More common in Asian populations and younger patients

— Often mistaken for appendicitis — CT clarifies

— Generally milder, more often managed nonoperatively; less likely to recur

Pregnancy:

Young adults (<40):

Immunocompromised (transplant, chronic steroids ≥20 mg/day prednisone equivalent, biologics, active chemo, advanced HIV, neutropenia):

Right-sided diverticulitis:

Key distinction: A young, healthy outpatient with mild left-sided diverticulitis can usually be managed with oral antibiotics at home; an immunosuppressed transplant patient with identical CT findings should be admitted on IV antibiotics with surgical consult, even if "looks well."

Board pearl: Solid-organ transplant + diverticulitis = admit, image, consult surgery — every time.

Complications and Adverse Outcomes

— Most common complication; suspect with persistent fever or leukocytosis on antibiotics

— Management: IV antibiotics + percutaneous drainage if ≥3–4 cm

— Failure to drain → surgery

— Sudden severe pain, peritonitis, sepsis, free air on imaging

— Emergent surgery (Hartmann or primary anastomosis with diversion)

— Mortality 5–15% (higher in elderly and immunocompromised)

— Colovesical (most common): pneumaturia, fecaluria, recurrent polymicrobial UTI — confirm with CT (air in non-instrumented bladder) ± cystoscopy

— Colovaginal: vaginal stool/gas, post-hysterectomy women

— Coloenteric, colocutaneous: rarer

— Management: elective single-stage resection with repair of secondary organ

— Acute: edema/inflammation; usually resolves with bowel rest + antibiotics

— Chronic: stricture from recurrent inflammation → elective resection

— Always exclude malignancy in the strictured segment

— Diverticular bleeding is distinct from diverticulitis (painless hematochezia from a non-inflamed diverticulum)

— Acute diverticulitis rarely bleeds significantly; if it does, reconsider diagnosis

— ~20–35% lifetime recurrence after first episode

— Higher with younger age, complicated initial episode, retained abscess, smoking, obesity, family history

— Most recurrences are uncomplicated and manageable nonoperatively

— Anastomotic leak (2–5%), wound infection, ileus, stoma complications, incisional hernia

— Hartmann reversal carries significant morbidity; ~30–50% never reversed

— Chronic smoldering diverticulitis or "symptomatic uncomplicated diverticular disease" (SUDD)

— Quality of life impairment and recurrent imaging exposure

— Stoma-related psychosocial burden

Abscess (Hinchey Ib/II):

Free perforation (Hinchey III/IV):

Fistula (5–15% of complicated disease):

Obstruction:

Bleeding:

Recurrence:

Postoperative complications:

Long-term sequelae:

Step 3 management: Failure to clinically improve in 48–72 hours mandates repeat CT to identify abscess, perforation, or alternate diagnosis (especially occult malignancy).

Board pearl: Recurrent polymicrobial UTI with pneumaturia in a middle-aged man = colovesical fistula from diverticulitis until proven otherwise.

When to Escalate — ICU, Consult, and Inpatient Triage

— Septic shock or vasopressor requirement

— Hinchey III/IV with hemodynamic instability

— Severe metabolic acidosis (lactate >4)

— Respiratory failure

— Postoperative hemodynamic instability

— Multiorgan dysfunction

— Any complicated diverticulitis on CT

— Peritonitis on exam

— Free perforation

— Abscess (even if planning IR drainage — surgery co-manages and plans interval resection)

— Failure of medical therapy at 48–72 h

— Fistula or obstruction

— Immunocompromised with any CT finding

— Drainable abscess ≥3–4 cm

— Source control in unstable surgical candidates

— Coordinating interval colonoscopy

— Stricture management considerations

— Bleeding evaluation if hematochezia present

— Resistant organisms, recurrent infections, complex antibiotic regimens

— Immunocompromised hosts with atypical pathogens

— Floor: stable vitals, IV antibiotics, no organ dysfunction, simple uncomplicated-but-needs-admission cases (e.g., can't tolerate PO)

— Step-down/telemetry: borderline sepsis, ongoing resuscitation, post-drainage monitoring

— ICU: as above

— Afebrile ≥24 h

— Tolerating PO including antibiotics

— Pain controlled on oral analgesics

— Down-trending WBC/CRP

— No new complications

— Follow-up arranged within 1–2 weeks, with interval colonoscopy in 6–8 weeks if indicated

ICU admission criteria:

Surgery consultation — call early for:

Interventional radiology consult:

Gastroenterology consult:

Infectious disease consult:

Inpatient floor vs step-down vs ICU triage:

CCS pearl: On a CCS diverticulitis case requiring admission, your typical order set is: IV access ×2, NS or LR bolus, NPO or clear liquids, IV ceftriaxone + metronidazole (or pip-tazo if severe), antiemetic, IV acetaminophen, VTE prophylaxis, surgery consult, repeat abdominal exam q4h, vitals q4h, CBC/BMP in AM, NPO if planning procedure. Don't forget to advance the clock and reassess.

Discharge readiness criteria:

Board pearl: Always document a clinical reassessment at 48–72 hours — this is the moment Step 3 stems use to test whether you recognize treatment failure and escalate.

Key Differentials — Same-Category (GI) Causes

— Classic RLQ pain, but redundant sigmoid loops can present LLQ pain mimicking diverticulitis; right-sided diverticulitis mimics appendicitis

— CT differentiates; both managed by surgery if complicated

— Younger patients, chronic diarrhea, weight loss, extraintestinal manifestations

— Crohn can involve sigmoid with skip lesions; CT may show wall thickening, mesenteric stranding

— Colonoscopy with biopsy distinguishes; managed medically (5-ASA, steroids, biologics), not antibiotics alone

— Older patient, sudden LLQ/abdominal pain, bloody diarrhea, often after hypotensive event

— Watershed areas (splenic flexure, rectosigmoid)

— CT: segmental wall thickening; colonoscopy: pale mucosa with hemorrhagic patches

— Supportive care; surgery if necrosis

— Can perforate and mimic complicated diverticulitis exactly

— Weight loss, change in stool caliber, iron-deficiency anemia, occult blood

— Mandatory interval colonoscopy after acute episode

— Diarrhea-predominant, often bloody, recent antibiotic exposure (C. diff)

— Stool studies, C. diff toxin/PCR

— Treat etiologically

— Painless brisk hematochezia, no inflammation

— Workup: colonoscopy ± CTA; not antibiotics

— Focal LLQ pain mimicking diverticulitis in a well-appearing patient with normal labs

— CT: small fat-density lesion with surrounding stranding

— Self-limited; treat with NSAIDs, no antibiotics, no surgery

— Chronically constipated, especially elderly; severe cases can perforate

— KUB/CT shows massive stool burden

— Chronic, no fever/leukocytosis, no CT findings — diagnosis of exclusion

Acute appendicitis:

Inflammatory bowel disease (Crohn, UC):

Ischemic colitis:

Colorectal cancer (especially sigmoid):

Infectious colitis (C. difficile, Shigella, Campylobacter, EHEC):

Diverticular bleeding:

Epiploic appendagitis / omental infarction:

Constipation/stercoral colitis:

Irritable bowel syndrome:

Key distinction: Epiploic appendagitis is the classic "looks like diverticulitis but isn't" CT diagnosis — recognizing it spares the patient antibiotics and admission.

Board pearl: A perforated sigmoid mass in an older patient should be assumed to be cancer until colonoscopy proves otherwise.

Key Differentials — Other-Category Causes

— Nephrolithiasis: colicky flank pain radiating to groin, hematuria; CT non-contrast for stones

— Pyelonephritis: fever, CVA tenderness, pyuria, bacteriuria

— UTI/cystitis: dysuria, frequency; pyuria; consider colovesical fistula if recurrent and polymicrobial

— Ectopic pregnancy: β-hCG positive, adnexal pain, possible shock — never miss

— Ovarian torsion: sudden severe pain, nausea, adnexal mass on US with absent Doppler flow

— Tubo-ovarian abscess / PID: cervical motion tenderness, adnexal tenderness, fever

— Endometriosis: cyclic pain

— Ruptured ovarian cyst: sudden pain, free fluid

— Abdominal aortic aneurysm (especially ruptured/leaking): older male smoker, hypotension, pulsatile mass, back/flank pain — emergent

— Mesenteric ischemia: "pain out of proportion to exam," atrial fibrillation or atherosclerosis; lactate elevated; CTA

— Aortoenteric fistula: prior aortic graft, GI bleed + abdominal pain

— Incarcerated/strangulated inguinal, femoral, or incisional hernia presenting with pain, obstruction, peritonitis

— Rectus sheath hematoma (anticoagulated patients); positive Carnett sign

— Muscle strain

— Psoas abscess, retroperitoneal hematoma — often associated with anticoagulation or recent procedure

— DKA can present with abdominal pain — check glucose, anion gap

— Adrenal crisis, porphyria (rare)

— Lower-lobe pneumonia, pulmonary embolism — atypical abdominal pain in some patients

— Inferior MI can cause epigastric pain — ECG and troponin in older patients with risk factors

Urologic:

Gynecologic (always consider in women):

Vascular:

Hernia complications:

Musculoskeletal/abdominal wall:

Retroperitoneal:

Systemic / metabolic:

Pulmonary referred:

Cardiac referred:

Step 3 management: A complete differential in LLQ pain requires β-hCG in any reproductive-age woman, urinalysis in all, lipase if epigastric component, ECG/troponin if cardiac risk, and CT to anchor or refute the diverticulitis diagnosis before committing to a treatment pathway.

Board pearl: Hypotensive elderly male smoker with abdominal/back pain = AAA until proven otherwise — bedside US first, do not delay for CT if unstable.

Secondary Prevention and Long-Term Plan

— High-fiber diet (25–35 g/day): fruits, vegetables, whole grains, legumes — reduces recurrence and progression

— Adequate hydration

— The old "avoid nuts, seeds, popcorn" advice is obsolete — large prospective data (Health Professionals Follow-up Study) showed no increased risk and possibly protective effect; patients should not be restricted

— Limit red and processed meats — associated with higher diverticulitis risk

— Moderate alcohol

— Smoking cessation: smoking increases recurrence and complication risk

— Weight loss / BMI optimization: obesity is a strong modifiable risk factor

— Regular physical activity (vigorous activity particularly) is associated with reduced recurrence

— Avoid chronic NSAID use when possible (perforation risk); use acetaminophen first; if NSAID needed, lowest effective dose with GI protection

— No proven benefit from mesalamine, rifaximin, or probiotics for prevention of recurrence on routine basis (mixed/negative trials); not standard of care

— Review and minimize opioids (constipation, masked symptoms)

— Optimize bowel regimen if chronic constipation

— Interval colonoscopy 6–8 weeks after first episode of complicated disease or any episode without recent (within ~1 year) high-quality colonoscopy

— Subsequent colonoscopy at standard age-appropriate intervals unless other indications arise

— Individualized based on episode frequency, severity, complications, immune status, quality of life — not strict episode count

— Shared decision-making addressing recurrence risk reduction (~70–80% reduction) vs perioperative morbidity (~10–20% complication rate, mortality <1% elective)

— Strong consideration in immunocompromised, recurrent complicated disease, fistula, stricture

— Update influenza, COVID-19, pneumococcal, herpes zoster, Tdap as age-appropriate — particularly important if elective surgery planned

Dietary modifications (post-recovery, long-term):

Lifestyle:

Medication considerations:

Surveillance:

Elective surgery discussion:

Vaccinations (general health maintenance):

Step 3 management: At discharge, document dietary counseling, smoking cessation referral, NSAID counseling, colonoscopy scheduling, and surgical follow-up if indicated. These are commonly missed items on Step 3 management questions.

Board pearl: Nuts, seeds, and popcorn are NOT restricted — this is a frequently tested counseling point.

Follow-Up, Monitoring, and Counseling

— Phone or in-person check at 48–72 hours — assess pain, fever, PO tolerance, antibiotic adherence

— Office visit at 1–2 weeks to confirm resolution

— Worsening or no improvement at 72 hours → return for re-imaging and admission consideration

— Return precautions explicitly documented: worsening pain, fever, vomiting, inability to tolerate PO, peritonitis signs

— Primary care or surgery clinic within 1–2 weeks of discharge

— Wound checks if surgical; drain management if percutaneous drain in place (IR follow-up, drain study before removal)

— Stoma teaching and WOC nurse referral if ostomy created

— Hartmann reversal planning at 3–6 months with surgery — discuss risks and benefits

— Daily clinical reassessment for inpatients: vitals, exam, PO tolerance, urine output

— Trend WBC and CRP if obtaining serial labs (typically every 1–2 days, not daily without reason)

— Repeat CT only if clinical deterioration or failure to improve — not routine

— Renal function and electrolytes if on nephrotoxic antibiotics or with ongoing volume issues

— Disease nature: diverticula are permanent; goal is to prevent recurrence and complications

— Recurrence rate (~20–35%) and warning signs

— Diet, lifestyle, and medication counseling (as above)

— Importance of interval colonoscopy to rule out cancer

— When to call vs when to go to ED

— Recurrent disease, chronic pain, or stoma can affect mental health — screen and refer as needed

— Address fears about food restrictions and lifestyle limitations with evidence-based reassurance

— Medication reconciliation at discharge — duration of antibiotics, analgesics, bowel regimen

— Clear handoff to PCP with discharge summary including pending colonoscopy

— Patient given written instructions in plain language

Outpatient follow-up (uncomplicated, discharged from ED or clinic):

Post-hospitalization follow-up:

Monitoring parameters during therapy:

Counseling content:

Mental health and quality of life:

Care transitions:

Step 3 management: A successful outpatient diverticulitis disposition has three checkpoints: 48–72 h reassessment, 1–2 week clinic visit, and 6–8 week colonoscopy. Missing any of these is a Step 3-flavored error.

Board pearl: Failure to arrange interval colonoscopy is one of the most common Step 3 management omissions tested.

Ethical, Legal, and Patient Safety Considerations

— Emergent surgery (Hartmann) in a septic patient may require two-physician emergency consent if patient lacks capacity and family is unreachable — document attempts and clinical justification

— Discuss realistic prognosis, stoma possibility, mortality, and potential need for further procedures before elective surgery — patients frequently underappreciate that Hartmann may not be reversible

— Document shared decision-making for elective resection — recurrence risk reduction vs perioperative morbidity

— Elderly or frail patients facing emergent surgery should have goals-of-care conversation early — preferably before sedation/decompensation

— Identify healthcare proxy and advance directives on admission

— Palliative care consult appropriate for high-mortality scenarios (Hinchey IV in frail elderly)

— Discharged patients on PO antibiotics may not return if worsening due to access, transportation, or insurance issues — explicit return precautions and scheduled follow-up calls mitigate this

— Medication reconciliation errors (duplicate or missed antibiotics) — pharmacist review valuable

— Pending colonoscopy can fall through the cracks — direct scheduling at discharge or warm handoff to GI improves completion rates

— Drain in place at discharge requires explicit instructions and follow-up appointment

— Diagnostic anchoring: don't assume recurrent LLQ pain is always diverticulitis — re-image and reconsider colorectal cancer or IBD

— Antibiotic stewardship: avoid unnecessarily broad or prolonged courses; document indication and planned duration

— Opioid stewardship: minimize prescriptions, screen for substance use disorder, offer naloxone if dispensing

— VTE prophylaxis in admitted patients — not routinely missed but commonly underdosed in obesity

— Not a reportable condition itself, but suspected elder abuse or neglect identified during care must be reported

— Document refusal of recommended interval colonoscopy or surgery in patients with capacity — informed refusal

— Access to interval colonoscopy varies by insurance and geography — proactive scheduling and financial counseling reduce disparities

Informed consent:

Capacity and goals of care:

Transitions-of-care risks (Step 3 favorite):

Patient safety / quality:

Reporting and legal:

Equity:

Step 3 management: When a patient with capacity refuses interval colonoscopy after complicated diverticulitis, document informed refusal, ensure they understand cancer risk, and offer reasonable alternatives (CT colonography) and re-engagement at next visit — do not coerce.

Board pearl: "Patient discharged on antibiotics, no follow-up arranged, returns with abscess" = a transition-of-care failure Step 3 will test as a safety question.

High-Yield Associations and Rapid-Fire Facts

— Outpatient: Cipro + metronidazole OR Amox-Clav × 4–7 days

— Inpatient: Ceftriaxone + metronidazole OR piperacillin-tazobactam × 7–10 days

Anatomy: Sigmoid is the most common site (Western); right-sided more common in Asian populations and younger patients.

Risk factors: Age >50, low-fiber/high-red-meat diet, obesity, smoking, sedentary lifestyle, chronic NSAID/steroid use, family history, connective tissue disorders (Ehlers-Danlos, Marfan), ADPKD.

Pathophysiology: Micro-perforation of a diverticulum, not stagnant fecalith — modern understanding.

Imaging gold standard: CT abdomen/pelvis with IV contrast.

Classification: Modified Hinchey (Ia phlegmon, Ib pericolic abscess, II distant abscess, III purulent peritonitis, IV feculent peritonitis).

Drainage threshold: Abscess ≥3–4 cm → percutaneous drainage.

Antibiotic regimens to memorize:

Emergency surgery: Hartmann for unstable/feculent peritonitis; primary anastomosis with diversion for stable purulent peritonitis.

Interval colonoscopy: 6–8 weeks after acute episode if not done within ~1 year.

Diet: High fiber; nuts/seeds/popcorn NOT restricted (myth).

Recurrence: ~20–35% lifetime; "≥2 episodes = surgery" rule is obsolete — decision is individualized.

Colovesical fistula triad: Pneumaturia, fecaluria, recurrent polymicrobial UTI; men > women.

Avoid in acute phase: Colonoscopy, sigmoidoscopy, barium enema.

Immunocompromised: Admit, broad-spectrum IV antibiotics, low threshold for surgery — even mild-appearing disease.

Pregnancy: US first, then MRI; ceftriaxone safe; surgery best in 2nd trimester.

Right-sided diverticulitis: Often mimics appendicitis; usually milder course.

Diverticular bleeding ≠ diverticulitis: Painless hematochezia, no antibiotics, workup is colonoscopy ± CTA.

Mortality: <1% uncomplicated; up to 20–30% in elderly with Hinchey IV emergent surgery.

NSAIDs: Increase perforation risk; counsel patients.

Smoking: Increases recurrence and complications — cessation counseling at every visit.

Step 3 management: Anchor every diverticulitis case on these three forks: CT severity, host status, PO tolerance → drives outpatient vs inpatient, antibiotics vs drainage vs surgery, and elective vs urgent surgery.

Board pearl: If a stem mentions transplant, biologic, chronic prednisone, or active chemo → admit regardless of how mild the CT looks.

Board Question Stem Patterns

"58-year-old healthy woman with 2 days of LLQ pain, T 37.9°C, WBC 12k, CT shows sigmoid wall thickening and pericolic fat stranding without abscess. Tolerating PO. Next step?"

→ Outpatient PO Cipro + metronidazole (or Amox-Clav), 4–7 days, 48–72 h follow-up, interval colonoscopy in 6–8 weeks.

"62-year-old kidney transplant patient on tacrolimus and prednisone with mild LLQ pain, T 37.6°C, WBC 9k, CT shows minimal pericolic stranding. Next step?"

→ Admit, IV ceftriaxone + metronidazole, surgical consult — never outpatient in this host.

"Patient with CT-confirmed 6 cm pelvic abscess. Next step?"

→ IV antibiotics + percutaneous CT-guided drainage. Surgery if drainage fails or anatomy precludes.

"Sudden diffuse abdominal pain, rigid abdomen, HR 120, BP 85/50, CT shows free air and feculent fluid."

→ Fluids, broad-spectrum IV antibiotics, emergent surgery — Hartmann procedure (unstable + feculent).

"Patient on day 3 of outpatient antibiotics, persistent fever and pain."

→ Re-image with CT, admit for IV antibiotics, look for abscess or alternate diagnosis.

"Recurrent UTIs with E. coli, Klebsiella, and Enterococcus; pneumaturia."

→ CT abdomen/pelvis (air in non-instrumented bladder), elective resection with fistula repair.

"Painless large-volume hematochezia in 75-year-old, hemodynamically stable."

→ Colonoscopy after rapid prep (not antibiotics — this is bleeding, not -itis).

"Patient recovered from first episode of complicated diverticulitis 6 weeks ago. Next step?"

→ Colonoscopy to exclude malignancy.

"Patient asks if she should avoid nuts and popcorn."

→ No restriction needed; encourage high-fiber diet.

"Frail 85-year-old with Hinchey IV and dementia."

→ Goals-of-care conversation with surrogate; surgical vs palliative path; document decision.

Stem 1 — Classic outpatient candidate:

Stem 2 — Immunocompromised trap:

Stem 3 — Abscess management:

Stem 4 — Free perforation:

Stem 5 — Failure to improve:

Stem 6 — Colovesical fistula:

Stem 7 — Diverticular bleed distractor:

Stem 8 — Interval colonoscopy timing:

Stem 9 — Counseling pitfall:

Stem 10 — Elderly emergent surgery ethics:

Step 3 management: Recognize the triage forks in each stem — host status, CT severity, response to therapy — and map to the correct disposition.

Board pearl: When the stem gives you a transplant or chronic steroid patient, do not pick outpatient management even if the CT looks bland.

One-Line Recap

— Diagnosis: CT abdomen/pelvis with IV contrast is the gold standard; never colonoscopy in the acute phase

— Outpatient criteria (all required): uncomplicated CT, tolerates PO, hemodynamically stable, immunocompetent, reliable follow-up

— Outpatient antibiotics: Cipro + metronidazole OR Amox-Clav × 4–7 days; new data suggest antibiotics may be omitted in highly selected immunocompetent mild cases, but default to treating on Step 3

— Inpatient antibiotics: Ceftriaxone + metronidazole; escalate to piperacillin-tazobactam for severe disease or sepsis

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

— Surgery: Hartmann for unstable/feculent peritonitis; primary anastomosis ± diversion for stable purulent peritonitis; elective resection individualized, not by episode count

— Interval colonoscopy: 6–8 weeks post-recovery if not recently done — exclude colon cancer

— Counseling: high-fiber diet, smoking cessation, weight management, avoid chronic NSAIDs; nuts/seeds/popcorn are NOT restricted

— Immunocompromised: admit every time, even with mild CT findings — blunted symptoms, fast progression

— Transition of care: 48–72 h check, 1–2 week clinic visit, 6–8 week colonoscopy — missing any is a Step 3 safety error

One-liner: Acute diverticulitis management hinges on a single triage decision — CT-confirmed uncomplicated disease in an immunocompetent patient who tolerates PO can be managed outpatient with oral antibiotics and 48–72 h follow-up, while complicated disease (abscess, perforation, fistula, obstruction), sepsis, immunosuppression, or PO intolerance mandates admission with IV antibiotics, surgical consult, and percutaneous drainage or surgery as indicated, followed by interval colonoscopy in 6–8 weeks to exclude malignancy.

Rapid recap bullets:

Board pearl: The single highest-yield Step 3 reflex in diverticulitis is: immunocompromised host = admit; abscess ≥4 cm = drain; Hinchey III/IV = surgery; and every patient = interval colonoscopy.