What type of ultrasound should be ordered to evaluate for appendicitis?

Ultrasound for Suspected Appendicitis

Order a graded-compression ultrasound of the right lower quadrant (or complete abdomen) as your initial imaging study for suspected appendicitis, particularly in children, adolescents, pregnant women, and young adults. 1, 2

Technical Specifications

The ultrasound examination should employ the graded compression technique, which involves:

• Progressive, deepening pressure with the transducer using both hands during patient exhalation 1
• Displacement of overlying bowel gas and intervening organs to bring the appendix closer to the transducer 1
• Systematic evaluation of all potential appendiceal locations, not just the classic right lower quadrant position 1
• Inclusion of still and cine images across all four abdominal quadrants with targeted right lower quadrant evaluation 3

Diagnostic Performance

Graded-compression ultrasound demonstrates:

• Sensitivity of approximately 76% and specificity of 95% when performed by radiologists 1, 4
• Higher accuracy (91% sensitivity, 97% specificity) when performed as point-of-care ultrasound by trained emergency physicians or surgeons 2, 4
• Excellent specificity in both pediatric and adult populations, making it highly reliable when positive 5

Population-Specific Recommendations

Children and Adolescents

Ultrasound is the mandatory first-line imaging modality to avoid ionizing radiation, regardless of clinical risk stratification. 1, 2, 4 The American College of Radiology designates this as the standard of care for all pediatric patients with suspected appendicitis. 1, 4

Pregnant Patients

Transabdominal ultrasound with graded compression is the preferred initial method, avoiding fetal radiation exposure. 1, 4 If ultrasound proves inconclusive, proceed to MRI without IV contrast (sensitivity 94%, specificity 96%) rather than CT. 2, 4

Non-Pregnant Adults

Ultrasound remains appropriate as first-line imaging to reduce radiation exposure, though CT with IV contrast (sensitivity 96-100%, specificity 93-95%) may be ordered directly in intermediate-to-high risk cases based on institutional protocols. 1, 2, 4 The staged approach of ultrasound followed by CT when needed achieves 99% sensitivity and 91% specificity overall. 2, 4

Young Women of Reproductive Age

After an inconclusive transabdominal ultrasound, order transvaginal ultrasound next (ACR appropriateness rating 5) before proceeding to CT, as it can identify gynecologic causes of right lower quadrant pain and visualize a pelvic appendix. 2, 4

Key Ultrasound Findings

Positive findings include:

• Appendiceal diameter ≥7 mm (some sources use >6 mm or >8.2 mm cutoffs) 4, 6
• Muscular wall thickness ≥3 mm combined with visualization of a complex mass (sensitivity 68%, specificity 98%) 6
• Non-compressibility of the appendix with graded compression 4
• Appendiceal tenderness during transducer pressure 4
• Periappendiceal fat stranding or echogenic mesenteric fat 3

Management After Ultrasound

If Ultrasound is Positive

Proceed immediately to surgical consultation and initiate broad-spectrum antibiotics covering aerobic gram-negative organisms and anaerobes. 4

If Ultrasound is Nondiagnostic or Equivocal

Do not repeat ultrasound. Instead, proceed directly to:

• CT abdomen/pelvis with IV contrast (no oral contrast needed) in non-pregnant adults and children when clinical suspicion persists 1, 2, 4
• MRI abdomen/pelvis without IV contrast as a radiation-free alternative, particularly in pregnant patients or children 1, 2, 4
• Clinical reassessment if suspicion has decreased during observation 5

If Ultrasound is Negative

When the appendix is visualized and appears normal with no secondary inflammatory findings, the negative predictive value is high and further imaging may not be needed. 2 However, if clinical suspicion remains high despite negative imaging, consider observation with 24-hour follow-up or proceed to CT/MRI. 4

Critical Limitations to Recognize

Ultrasound has low sensitivity (33.9-51.5%) for detecting perforated appendicitis, which is a major limitation when perforation status influences management decisions. 4, 3 Specific findings highly specific (>90%) for perforation include appendiceal wall thinning and loculated fluid collections in the right lower quadrant. 3

Non-visualization of the appendix is common and does not exclude appendicitis—approximately 26% of patients with equivocal ultrasound (appendix not seen but inflammatory signs present) ultimately have appendicitis. 4 In North America, appendix visualization rates are lower than in Europe and Asia. 1

Accuracy is highly operator-dependent and can be compromised by patient body habitus, bowel gas, and retrocecal appendix position (present in up to 65% of patients). 4, 7, 5

Advanced Techniques

For difficult cases, consider:

• Posterior manual compression technique as an adjunct, which can increase appendix visualization from 85% to 95% of cases 8
• Novel transducer and patient positioning for suspected retrocecal appendicitis 7
• Point-of-care ultrasound by emergency physicians when available, as it demonstrates superior performance compared to traditional radiology-performed studies 2, 4