Technique: Apply graded compression at the point of maximum RLQ tenderness, progressively displacing overlying bowel gas. Normal appendix: <6 mm, compressible, no surrounding fat stranding. Non-visualization does NOT exclude appendicitis — proceed to CT in adults if clinically indicated.
Diagnostic Findings
| Finding | Sensitivity | Specificity |
|---|---|---|
| Appendix >6 mm, non-compressible, blind-ending | ~75–85% | ~90–95% |
| Periappendiceal hyperechoic fat stranding | ~70% | ~93% |
| Appendicolith (shadowing echogenic focus) | ~25–35% | ~99% |
| Perforation (loss of wall layers, free fluid) | ~50% | ~95% |
| Hyperemia on color Doppler | ~87% | ~96% |
Operator and patient factors: Highly operator-dependent; best results in thin patients and children. Non-visualization rate ~20–30% in adults. If the appendix cannot be visualized and clinical suspicion remains, CT is indicated in adults. In pregnancy, MRI is preferred over CT for equivocal cases.
Imaging Algorithm
- Children / pregnancy: Ultrasound first
- Non-diagnostic US in adults: CT abdomen/pelvis
- Non-diagnostic US in pregnancy: MRI (avoid CT if possible)
Reference
Radiopaedia — Acute appendicitis (ultrasound)