Acute Diverticulitis: Most Likely Diagnosis and Management
Most Likely Diagnosis
In a patient with known diverticulosis presenting with fever, lower abdominal pain, and low back pain, acute diverticulitis is the most likely diagnosis and requires immediate CT abdomen/pelvis with IV contrast to confirm the diagnosis and identify complications. 1, 2
Why This Presentation Suggests Diverticulitis
Acute sigmoid diverticulitis is the most common cause of left lower quadrant pain in adults, especially those over 50 years of age. 2
The combination of lower abdominal pain, fever, and known diverticulosis creates high clinical suspicion for acute diverticulitis, though the classic triad of left lower quadrant pain, fever, and leukocytosis occurs in only approximately 25% of cases. 2
Lower back pain can occur with diverticulitis due to retroperitoneal inflammation or extension of the inflammatory process. 3
Clinical examination alone misdiagnoses diverticulitis in 34–68% of cases, making imaging mandatory rather than optional. 2, 4
Immediate Diagnostic Work-Up
Imaging (First Priority)
Order CT abdomen and pelvis with IV contrast immediately—this is the gold standard diagnostic test with 98–99% sensitivity and 99–100% specificity. 1, 5
The American College of Radiology rates CT abdomen/pelvis with IV contrast as 8/9 (usually appropriate) for this clinical scenario. 2
CT will identify:
- Pericolonic fat stranding and bowel wall thickening (diagnostic hallmarks of diverticulitis) 4
- Abscess formation (size determines drainage strategy) 6
- Free perforation or extraluminal air 6
- Fistula, obstruction, or phlegmon 1
- Alternative diagnoses including perforated colon cancer, which can mimic diverticulitis 2
Do not order plain abdominal radiographs—they have low sensitivity (49% for obstruction, even lower for diverticulitis) and will delay definitive diagnosis. 1
Do not order non-contrast CT—it has limited sensitivity for detecting the pericolonic inflammation that defines diverticulitis. 4
Laboratory Testing
Obtain the following labs immediately: 6, 7
- Complete blood count with differential (leukocytosis with left shift suggests bacterial infection)
- C-reactive protein (CRP >50 mg/L supports diverticulitis; CRP >170 mg/L predicts severe disease with 87.5% sensitivity)
- Basic metabolic panel (assess for electrolyte abnormalities and renal function)
- Lactate level (elevated lactate suggests tissue hypoperfusion from abscess, sepsis, or bowel ischemia)
Management Algorithm Based on CT Findings
Uncomplicated Diverticulitis (No Abscess, Perforation, or Other Complications)
For immunocompetent patients with uncomplicated diverticulitis, conservative management WITHOUT antibiotics is the standard recommendation. 6, 2, 5
- Clear liquid diet with advancement as tolerated 2
- Pain control with acetaminophen (avoid NSAIDs as they increase perforation risk) 5
- Outpatient management is appropriate if the patient can tolerate oral intake, has adequate pain control, has reliable follow-up, and has no immunocompromise or severe comorbidities 8
Reserve antibiotics for high-risk patients only: 5, 8
- Persistent fever or chills despite initial management
- Increasing leukocytosis
- Age >80 years
- Pregnancy
- Immunocompromised state (chemotherapy, high-dose steroids, organ transplant)
- Chronic medical conditions (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes)
If antibiotics are indicated, use: 5
- Outpatient: Oral amoxicillin/clavulanic acid OR cefalexin plus metronidazole
- Inpatient (if unable to tolerate oral intake): IV cefuroxime or ceftriaxone plus metronidazole, OR IV ampicillin/sulbactam
Complicated Diverticulitis with Small Abscess (<4 cm)
Antibiotics alone for 7 days without drainage. 6, 2
- IV antibiotics: ceftriaxone plus metronidazole OR piperacillin-tazobactam 5
- Hospital admission required 6
Complicated Diverticulitis with Large Abscess (≥4 cm)
Percutaneous CT-guided drainage PLUS IV antibiotics for 4 days. 6, 2
- Same antibiotic regimen as above 5
- Surgical consultation for drainage planning 6
- Stop antibiotics at 4 days if source control is adequate in immunocompetent, non-critically ill patients. 2
Free Perforation or Peritonitis
Immediate surgical consultation for emergency laparotomy. 6, 2
- Broad-spectrum IV antibiotics (ceftriaxone plus metronidazole OR piperacillin-tazobactam) 5
- NPO and IV fluid resuscitation 6
- Surgical options include primary resection with anastomosis (stable patients) or Hartmann's procedure (critically ill patients) 5
Critical Pitfalls to Avoid
Do not assume uncomplicated disease based on relatively normal vital signs—fever is present in only a minority of diverticulitis cases, and diabetic or elderly patients present atypically. 6, 2
Do not attribute symptoms to known diverticulosis without imaging—this is one of the most common diagnostic errors, and perforated colon cancer can mimic diverticulitis. 2, 4
Do not rely on clinical examination alone—the misdiagnosis rate is 34–68% without imaging. 2, 4
Watch for CT features suggesting colon cancer rather than diverticulitis: pericolonic lymphadenopathy >1 cm in short axis, luminal mass, or abnormal lymph nodes. 2
Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases antibiotic resistance without improving outcomes. 2
If symptoms persist beyond 2–3 days despite appropriate management, obtain repeat CT imaging to assess for complications or alternative diagnoses. 2, 4
Follow-Up Considerations
Colonoscopy is NOT routinely required after CT-confirmed uncomplicated diverticulitis unless the patient is due for age-appropriate screening or CT shows concerning features (abscess, perforation, fistula, abnormal lymph nodes, or luminal mass). 2, 7
If colonoscopy is indicated, delay it for 4–6 weeks after symptom resolution to reduce procedural risk. 7