What is the recommended initial imaging study for right lower quadrant abdominal pain, particularly when suspecting appendicitis?

Imaging for Right Lower Quadrant Abdominal Pain

For patients with right lower quadrant pain and suspected appendicitis, CT of the abdomen and pelvis with IV contrast is the recommended initial imaging study due to its high diagnostic accuracy. 1

Initial Imaging Selection Algorithm

Non-pregnant Adults:

• CT abdomen and pelvis with IV contrast is the first-line imaging modality (rated 8/9 on ACR Appropriateness Criteria) 1
  • Provides high sensitivity (85.7-100%) and specificity (94.8-100%) 1
  • Oral or rectal contrast may not be needed depending on institutional preference 1
  • Allows identification of alternative diagnoses that may mimic appendicitis 2

Radiation Reduction Strategies:

• Ultrasonography as initial screening (rated 6/9 on ACR Appropriateness Criteria) 1

  • Use graded compression technique 1
  • Follow with CT only if ultrasonography is inconclusive or negative 1
  • This approach significantly decreases CT use while maintaining diagnostic accuracy 1

• Low-dose CT protocols can reduce radiation exposure to approximately 22% of standard-dose protocols without significant difference in negative appendectomy rates 1

Special Populations:

Pregnant Patients:

• MRI abdomen and pelvis without IV contrast OR ultrasound abdomen is the primary modality 1
  • Avoids ionizing radiation exposure 1
  • MRI has superior appendix visualization rates (80%) compared to ultrasound (7%) 1
  • MRI demonstrates excellent sensitivity (100%) and specificity (98%) 1
  • Reserve CT only for cases with equivocal US and MRI findings 1

Women with Pelvic Pain:

• Pelvic ultrasonography (rated 5/9 on ACR Appropriateness Criteria) should be considered 1
  • Helps evaluate for gynecologic causes of pain 2

Clinical Considerations

Diagnostic Performance:

• CT has reduced negative appendectomy rates from historical 14.7% to 1.7-7.7% 1
• Complete abdominal and pelvic CT (not just focused on RLQ) increases sensitivity from 88% to 99% by identifying pathology outside the pelvis 3

Radiation Concerns:

• Abdominal CT exposes patients to approximately 10 mSv (compared to annual background radiation of 3 mSv) 1
• Balancing diagnostic accuracy with radiation exposure is essential, particularly in younger patients 1

Alternative Diagnoses:

• CT can identify numerous non-appendiceal causes of RLQ pain including 2, 4:
  • Primary epiploic appendagitis 4
  • Right-sided diverticulitis 4
  • Torsion of Meckel's diverticulum 4
  • Gynecologic disorders 4
  • Obstructive uropathy 4
  • Right lower lobe pneumonia 4

Common Pitfalls:

• Relying solely on conventional radiography, which has limited diagnostic value for assessing abdominal pain 1
• Using focused RLQ imaging only, which may miss pathology outside the pelvis that requires surgical intervention 3
• Delaying diagnosis due to oral contrast protocols, which may increase risk of perforation 1

Summary of ACR Recommendations

• Classic presentation: CT abdomen and pelvis with IV contrast 1
• Atypical presentation: CT abdomen and pelvis with IV contrast 1
• Pregnant patients: MRI abdomen and pelvis without IV contrast OR ultrasound abdomen 1