CT and Ultrasound Findings
| Finding | CT | US | Notes |
|---|---|---|---|
| Appendix diameter >6 mm | Outer wall–outer wall; distended with fluid | Non-compressible tubular structure >6 mm | Primary criterion; measure at widest point |
| Periappendiceal fat stranding | Haziness/streaking in periappendiceal fat | Echogenic surrounding fat | Increases specificity when combined with dilation |
| Appendicolith | Calcified focus within appendiceal lumen; extraluminal if perforated | Shadowing echogenic intraluminal focus | ~30% of cases; associated with perforation/gangrene |
| Wall enhancement/thickening | Stratified wall enhancement; wall >2 mm | Hyperechoic mucosa with thickened layers | Loss of enhancement = gangrenous/necrotic wall |
| Perforation signs | Free air (RLQ), periappendiceal abscess (rim-enhancing collection), phlegmon | Free fluid RLQ; disrupted wall layers | Perforation rate ~20–30%; IR drainage for abscess >3 cm |
| Non-visualization | May be normal (retrocecal, pelvic) or suggest alternative diagnosis | Non-visualization common (~20–30%); proceed to CT in adults | Always report explicitly — do not call normal |
Perforated and Gangrenous Appendicitis
Perforated appendicitis:
- Localized free extraluminal air in RLQ
- Periappendiceal abscess
- Phlegmon (ill-defined mass without discrete rim)
- Free fluid in RLQ/pelvis
Gangrenous appendicitis:
- Absent mural enhancement
- Intraluminal gas
- Focal wall defect
Both require urgent surgical or IR consultation.
Pearls
State diameter + fat stranding + appendicolith separately in report. Retrocecal appendix (~26%): may present with flank pain — ensure full coronal/sagittal review. Tip appendicitis: isolated inflammation of the tip, may be subtle.
Reporting Checklist
- Appendix diameter: measure outer wall to outer wall (mm; >6 mm abnormal)
- Periappendiceal fat stranding: present / absent
- Appendicolith: present / absent; location (tip / body / base)
- Wall enhancement: normal stratified / loss of mural enhancement (gangrenous)
- Perforation signs: localized free air / phlegmon / abscess (size if present)
- Appendix position: retrocecal / pelvic / pre-ileal / other
- Free fluid: present / absent; location
- Alternative diagnosis if appendix not visualized
References
Radiopaedia — Acute appendicitis