What is the appropriate diagnostic workup and treatment plan for a patient with suspected acute sigmoid diverticulitis presenting with left lower quadrant pain radiating to the leg?

Treatment of Acute Sigmoid Diverticulitis

For a patient with suspected acute sigmoid diverticulitis presenting with left lower quadrant pain, obtain CT abdomen/pelvis with IV contrast immediately to confirm diagnosis and guide treatment—this achieves 98% diagnostic accuracy and prevents unnecessary hospitalizations by distinguishing uncomplicated cases (managed outpatient with antibiotics) from complicated cases requiring drainage or surgery. 1

Diagnostic Workup

Initial Imaging Strategy

• CT abdomen/pelvis with IV contrast is the gold standard for suspected diverticulitis, with 98% diagnostic accuracy and superior ability to detect complications (abscess, perforation, fistula, obstruction) that alter management 1

• IV contrast is essential for characterizing bowel wall abnormalities and detecting abscesses, though unenhanced CT remains more accurate than clinical assessment alone if contrast is contraindicated 1

• Low-dose CT protocols (50-90% radiation reduction) maintain equivalent sensitivity and specificity to standard-dose CT and should be requested when available 1, 2

• Early CT reduces hospital admissions by >50% and shortens length of stay by identifying uncomplicated cases suitable for outpatient management 1

Critical Diagnostic Pitfalls to Avoid

• Do not rely on clinical assessment alone—misdiagnosis rates range from 34-68% even when the classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of cases 1

• Avoid plain radiography as it is extremely limited, detecting only large amounts of free air while missing small perforations and providing no bowel wall information 1, 2

• Do not order contrast enema as it only shows secondary mucosal effects, misses extraluminal abscesses, and increases perforation risk with colonic distention 1, 2

• Ultrasound is not first-line in the United States—it is operator-dependent, limited by body habitus, and has significantly lower sensitivity (61% vs 81% for CT) for detecting diverticulitis and alternative diagnoses 1, 2

• MRI is not appropriate for acute evaluation due to limited emergency availability, longer acquisition times, and motion artifacts in acutely ill patients 1, 2

Special Population Considerations

• In premenopausal women with left lower quadrant pain, obtain transvaginal ultrasound first if gynecologic pathology (ectopic pregnancy, pelvic inflammatory disease) is suspected, then proceed to CT if ultrasound is equivocal or nongynecologic etiology is likely 1

Treatment Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, No Perforation)

• Outpatient management with oral broad-spectrum antibiotics covering aerobic and anaerobic bacteria for 7-10 days is appropriate for most patients 1, 3

• Hospitalization is indicated only if: patient cannot tolerate oral intake, has severe systemic symptoms, shows signs of peritonitis, or fails to improve with outpatient therapy after 2-3 days 3

• Imaging may be omitted in highly selected patients with typical symptoms, prior documented diverticulitis with similar presentation, and no evidence of complications—though there is a trend toward imaging all cases given high misdiagnosis rates 1

Complicated Diverticulitis with Abscess

• Catheter drainage is indicated for abscesses ≥3 cm in size, allowing medical management to succeed without surgery 1

• Medical therapy alone (antibiotics without drainage) is appropriate for locally perforated diverticulitis without a drainable collection 1

• Repeat CT imaging within 2-3 days is mandatory if no clinical improvement occurs, as this may reveal evolving abscess, phlegmon, or fistula requiring intervention 3

Complicated Diverticulitis with Free Perforation

• Emergency surgery is indicated for free perforation with peritonitis 1

Follow-Up and Recurrence Prevention

Predicting Recurrence Risk

• Colonic wall thickness <9 mm on CT predicts only 19% recurrence risk and may guide surveillance versus operative management 1

• Extent of diverticulitis-related complications on initial CT also predicts recurrence likelihood 1

Long-Term Outcomes: Conservative vs. Surgical Management

• Conservatively treated patients have 32.5% recurrence rates during follow-up compared to only 3.5% after sigmoid resection 4

• Persistent symptoms occur in 25% of conservative management versus 8.8% after surgery, including painful defecation (22.5% vs 8.8%), constipation (25% vs 8.8%), abdominal cramping (22.5% vs 4.4%), and painful flatulence (25% vs 8.8%) 4

• Surgical complications include sexual dysfunction (7%) and bladder dysfunction (9%) postoperatively 4

Clinical Follow-Up Strategy

• Close follow-up within 24-48 hours is necessary after initiating outpatient treatment to reassess for evolving symptoms 5

• Return precautions must be clearly communicated: return immediately if fever develops, pain worsens, inability to pass gas/stool occurs, or vomiting begins 5

• Do not attribute pain to incidental diverticulosis seen on CT—diverticulosis without inflammation does not cause pain 5

• Colonoscopy is not routinely indicated after negative CT unless the patient is due for age-appropriate colon cancer screening or has abnormal pericolic lymph nodes on CT 5

Red Flag Symptoms Requiring Emergency Evaluation

Immediate emergency department assessment is mandatory if the patient presents with: 5

• Fever combined with inability to pass gas or stool
• Severe abdominal tenderness with guarding or rebound
• Vomiting with progressive worsening pain
• Bloody stools
• Signs of shock (hypotension, tachycardia, altered mental status)
• Toxic appearance

Management When CT is Negative

• Obtain laboratory studies including complete blood count with differential and C-reactive protein to assess for occult inflammation 5

• MRI abdomen/pelvis with gadolinium is the preferred alternative if IV contrast was contraindicated and clinical suspicion remains high, with 86-94% sensitivity for inflammatory conditions 5

• Do not rely on non-contrast CT as it severely limits sensitivity for abscess formation, subtle bowel wall inflammation, and pericolonic changes that are only visible with contrast enhancement 2, 5