What is the appropriate evaluation and management for a 16-week pregnant woman presenting with right upper quadrant (RUQ) pain?

Evaluation and Management of RUQ Pain at 16 Weeks Gestation

Begin with ultrasound of the abdomen immediately, and if non-diagnostic, proceed directly to MRI abdomen and pelvis without IV contrast—this sequential approach achieves 100% sensitivity and 98.3% specificity for identifying surgical emergencies and alternative diagnoses in pregnant patients. 1

Initial Imaging Strategy

Ultrasound is the mandatory first imaging study for all pregnant patients presenting with RUQ pain, regardless of clinical presentation. 1, 2 At 16 weeks gestation (second trimester), ultrasound performs better than in later pregnancy, with appendix visualization rates of approximately 75% in the first trimester declining to 37% by the third trimester. 3 However, ultrasound alone has limited sensitivity (12.5%) for appendicitis in pregnancy, though specificity remains excellent at 99.2%. 1

When Ultrasound is Non-Diagnostic

Proceed immediately to MRI abdomen and pelvis without IV contrast if ultrasound fails to visualize the appendix or identify pathology. 1 This is critical because:

• MRI demonstrates pooled sensitivity of 96.8%, specificity of 99.2%, and negative predictive value of 99.7% for appendicitis in pregnancy 3, 1
• MRI visualizes the appendix in 70-80% of cases compared to only 7% with ultrasound 1
• MRI identifies alternative diagnoses in 10.1-43% of cases, which is crucial given the broad differential for RUQ pain in pregnancy 3, 1

The sequential ultrasound-then-MRI approach achieves diagnostic performance with 100% sensitivity, 98.3% specificity, 80% PPV, and 100% NPV. 1

Critical Differential Diagnoses for RUQ Pain at 16 Weeks

At this gestational age, consider:

• Appendicitis: The appendix may be displaced superiorly by the gravid uterus at 16 weeks, causing RUQ rather than RLQ pain 4
• Biliary pathology: Cholecystitis and choledocholithiasis (ultrasound is excellent for detecting gallstones and biliary dilation) 5
• Urolithiasis or pyelonephritis: Right-sided renal colic can present as RUQ pain 2
• Hepatic pathology: Though less common at 16 weeks, consider hepatic abscess, particularly in patients with inflammatory bowel disease 6
• Obstetric causes: Evaluate for placental abruption or other pregnancy-related complications 4

Timing and Urgency Considerations

Do not delay imaging or surgical consultation. 1, 2 Key red flags requiring immediate escalation include:

• Fever, tachycardia, or signs of sepsis (suggests pyelonephritis, appendicitis, or cholangitis) 2
• Hemodynamic instability 1
• Peritoneal signs on examination 7
• Leukocytosis with left shift (significantly associated with surgical pathology in pregnancy) 7

If appendicitis is confirmed, surgery should be performed within 24 hours to minimize perforation risk, which carries significant maternal and fetal morbidity. 8

Role of CT Imaging

Reserve CT abdomen and pelvis only for life-threatening situations where MRI is unavailable or both ultrasound and MRI remain equivocal. 1, 2 While CT maintains high sensitivity and specificity throughout pregnancy 7, radiation exposure concerns make it third-line. However, maternal health takes absolute priority—CT should not be withheld if maternal survival is at risk. 1

Common Pitfalls to Avoid

• Do not assume physiologic changes explain the pain. While pregnancy causes anatomical displacement and altered lab values, dismissing symptoms as "normal pregnancy discomfort" delays diagnosis of surgical emergencies. 4
• Do not rely on leukocyte count alone. Pregnancy causes physiologic leukocytosis, but a left shift (bandemia) is more specific for infection or inflammation requiring intervention. 7
• Do not skip MRI if ultrasound is non-diagnostic. The 97% non-visualization rate of the appendix on ultrasound in some studies means negative ultrasound does not exclude appendicitis. 3
• Do not delay surgical consultation. Even with negative imaging, if clinical suspicion remains high based on examination findings and laboratory trends, surgical evaluation is warranted. 1

Laboratory Evaluation

Obtain complete blood count with differential (looking specifically for left shift, not just elevated WBC), comprehensive metabolic panel, liver function tests, lipase, and urinalysis with culture. 7, 6 Elevated transaminases suggest hepatobiliary pathology, while pyuria indicates urinary tract infection or nephrolithiasis. 2, 6