What is the next step in managing a patient with left lower quadrant (LLQ) pain and a negative computed tomography (CT) scan, considering potential causes such as diverticulitis, and taking into account their past medical history and symptoms?

Management of Left Lower Quadrant Pain with Negative CT Scan

When a patient presents with left lower quadrant pain and a negative CT scan, the critical next step is to determine whether the CT was performed with IV contrast—if not, the study is inadequate and contrast-enhanced CT must be obtained to definitively exclude diverticulitis and other inflammatory processes. 1, 2

Immediate Assessment: Was the CT Adequate?

The first priority is verifying the CT protocol used:

• Non-contrast CT has severely limited sensitivity for detecting the pericolonic fat stranding, bowel wall thickening, and inflammatory changes that define diverticulitis 2
• CT with IV contrast achieves 98-100% diagnostic accuracy for diverticulitis and inflammatory conditions, compared to significantly reduced accuracy without contrast 3, 1, 2
• If the initial CT was performed without IV contrast, it should be considered inadequate for excluding diverticulitis, and repeat imaging with proper contrast enhancement is mandatory 1, 2

Why This Matters

Non-contrast CT can miss critical findings including abscess formation, subtle bowel wall inflammation, and pericolonic inflammatory changes that are only visible with contrast enhancement 1, 2. The American College of Radiology rates CT with IV contrast as 8/9 (usually appropriate) versus only 6/9 for non-contrast CT 4.

If CT With IV Contrast Was Truly Negative

When a properly performed contrast-enhanced CT is negative, proceed with the following algorithm:

1. Assess for Red Flag Symptoms Requiring Emergency Evaluation

Immediate emergency department evaluation is required if any of the following are present:

• Fever combined with inability to pass gas or stool 4
• Severe abdominal tenderness with guarding or rebound 4
• Vomiting with progressive worsening pain 4
• Bloody stools or signs of shock 4
• Toxic appearance (rapid breathing, rapid heartbeat, confusion) 4

These symptoms suggest complications such as perforation, obstruction, or sepsis that may not be visible on imaging but require urgent intervention 4.

2. Check Inflammatory Markers

Obtain laboratory studies to assess for occult inflammation:

• Complete blood count with differential (left shift >75% suggests bacterial infection) 4
• C-reactive protein (CRP >50 mg/L combined with left lower quadrant tenderness and absence of vomiting has 97% accuracy for diverticulitis, though this triad occurs in only 24% of patients) 4
• Elevated inflammatory markers despite negative CT may indicate early or mild disease not yet visible on imaging 2

3. Consider Alternative Imaging if Contrast CT Was Contraindicated

If IV contrast was contraindicated and non-contrast CT was performed:

• MRI abdomen/pelvis with gadolinium is the preferred alternative, with 86-94% sensitivity and 88-92% specificity for inflammatory conditions 2
• MRI may miss small amounts of extraluminal air but is superior to non-contrast CT for detecting inflammatory processes 3, 2

4. Evaluate for Alternative Diagnoses

With a truly negative contrast-enhanced CT, consider:

• Gynecologic pathology in premenopausal women: Order pelvic/transvaginal ultrasound if not already performed, as gynecologic and non-gynecologic pathology can present identically 3, 4
• Functional bowel disorders: If pain is related to bowel movements or dietary triggers and all structural pathology is excluded 2
• Atypical appendicitis: Rarely, appendicitis can present with left lower quadrant pain due to long appendix projecting leftward or situs inversus 5, 6
• Right-sided diverticulitis mislocalized: In 1.5% of cases, right-sided diverticulitis can present with atypical pain patterns 7

5. Clinical Follow-Up Strategy

For patients with negative imaging and no red flags:

• Outpatient management is appropriate if pain is mild and stable, patient can tolerate oral intake, and no signs of peritonitis are present 4
• Clear liquid diet advancement with pain control using acetaminophen (avoid NSAIDs as they increase diverticulitis risk) 8, 9
• Close follow-up within 24-48 hours to reassess for evolving symptoms 4
• Return precautions: Instruct patient to return immediately if fever develops, pain worsens, inability to pass gas/stool occurs, or vomiting begins 4

Critical Pitfalls to Avoid

Do not attribute pain to incidental diverticulosis seen on CT—this is one of the most common diagnostic errors, as diverticulosis without inflammation does not cause pain 2. The presence of diverticula without pericolonic fat stranding, bowel wall thickening, or complications is not diverticulitis 2.

Do not order routine colonoscopy after negative CT—colonoscopy is not indicated unless the patient is due for age-appropriate colon cancer screening, has abnormal pericolic lymph nodes on CT, has a luminal mass on CT, or the diagnosis remains uncertain 4. Colonoscopy does not diagnose acute diverticulitis and should be delayed 6 weeks after any acute episode if indicated 8.

Do not rely on clinical examination alone—misdiagnosis rates based on clinical assessment alone range from 34-68%, and the classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases 3, 4.

When to Repeat Imaging

Repeat contrast-enhanced CT is indicated if:

• Initial CT was non-contrast or inadequate 1, 2
• Clinical symptoms worsen or fail to improve within 48-72 hours 4
• New red flag symptoms develop during observation 4
• Inflammatory markers are significantly elevated despite negative imaging 2, 4