Should I order a CT abdomen or ultrasound for a patient with left lower quadrant pain?

CT Abdomen is the Recommended Imaging for Left Lower Quadrant Pain

CT abdomen with IV contrast should be ordered as the first-line imaging modality for a patient with left lower quadrant pain of 4 months duration, as it has superior diagnostic accuracy and can detect a wider range of pathologies compared to ultrasound. 1

Rationale for CT as First Choice

• The American College of Radiology (ACR) specifically recommends CT as the initial imaging test for evaluation of left lower quadrant pain 1
• CT has a sensitivity greater than 95% for detecting diverticulitis, which is a common cause of LLQ pain 1
• CT provides comprehensive information about:
  • Extent of disease
  • Presence of abscess formation
  • Alternative diagnoses with similar clinical presentations 1
• The 2023 ACR Appropriateness Criteria update confirms CT abdomen and pelvis as the most useful examination for left lower quadrant pain 1

Limitations of Ultrasound for LLQ Pain

• Ultrasound has shown variable sensitivity for diverticulitis (77-98%) and specificity (80-99%), but results are highly operator-dependent 1
• Direct comparison studies show CT has significantly higher sensitivity than ultrasound (81% vs 61%, p=0.048) 1
• Ultrasound is more limited by patient body habitus than CT 1
• Ultrasound is less likely to reveal alternative diagnoses for left lower quadrant pain 1

Special Considerations

• For female patients of reproductive age: If gynecologic pathology is suspected, transvaginal ultrasound may be appropriate as the initial test 1
• For pregnant patients: Ultrasound should be considered first to avoid radiation exposure 2
• For patients with renal insufficiency: Non-contrast CT can still be valuable with sensitivity and specificity for urinary tract calculi near 100% 1

Radiation Concerns

• CT abdomen exposes a patient to approximately 10 mSv of radiation (compared to annual background radiation of 3 mSv) 1
• For patients where radiation is a significant concern, ultrasound could be performed initially, with CT reserved for cases with non-diagnostic ultrasound results 2, 3

Clinical Implications

• The chronic nature of the pain (4 months) suggests a non-emergent condition but warrants thorough evaluation
• CT findings will likely have a marked effect on management decisions 3
• CT is cost-effective in the evaluation of acute abdominal pain 3

Bottom Line

For a patient with LLQ pain of 4 months duration, CT abdomen with IV contrast is the most appropriate initial imaging study based on current guidelines, as it offers the highest diagnostic accuracy and can detect the widest range of pathologies that could be causing the patient's symptoms.