Estimated reading time: 3 minutes
Appendix is a small, blind-ended tubular structure from the cecum, and its inflammation, appendicitis, is a frequent cause of acute abdomen needing surgery. Imaging is important in the diagnosis of appendicitis and in the differentiation from mimics. This blog discusses the imaging modalities to evaluate the appendix and their utility in diagnosis.
Role of Imaging in Appendicitis
The main function of radiology in appendicitis is to exclude the removal of a normal appendix. This calls for proper localization of the appendix and identification of signs of inflammation. Ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) all have a role to play in assessing appendicitis, each having its own strength and weakness.
Imaging Modalities
1. Ultrasound (US)
- Initial imaging modality, particularly in children and pregnant women.
- Uses a graded compression method to outline the appendix by pushing aside overlying bowel loops.
- US features of appendicitis:
- Blind-ending tubular structure with origin from the cecum.
- Non-compressible, aperistaltic, with a gut signature (hyperechoic mucosa, hypoechoic muscularis, hyperechoic serosa).
- Diameter >6 mm indicates inflammation.
- Hyperemia and stranding of periappendiceal fat, and free fluid.
- Probe tenderness, which is parallel to peritoneal inflammation.
- Tips for finding the appendix on US:
- Begin with a curvilinear probe for survey.
- Begin with identification of the ileocecal junction.
- Look 2–3 cm caudal to the ileocecal junction for the appendix.
- Use a high-resolution linear probe for clear imaging.
- Left lateral decubitus positioning may be considered if the appendix is not seen initially.
2. Computed Tomography (CT)
- Senti and specificest modality for the diagnosis of appendicitis (>95% sensitivity).
- Usually done as a contrast-enhanced CT (CCT) abdomen in India.
- In a few facilities (e.g., in the U.S.), a limited appendicitis CT (from subhepatic region to pelvis) can be done.
- CT Features of Appendicitis:
- Dilated appendix (>6 mm in diameter).
- Wall thickening and enhancement.
- Stranding of periappendiceal fat.
- Appendicolith (in certain cases).
- Abscess or perforation in complicated cases.
- No oral contrast required; there is no reduction in accuracy with or without oral contrast.
3. Magnetic Resonance Imaging (MRI)
- Used almost exclusively for pregnant patients in whom radiation exposure cannot be tolerated.
- Routine sequences are T1, T2, and diffusion-weighted imaging (DWI).
- Findings are the same as on CT but have longer acquisition times.
Clinical Considerations
- Mantrell Score: A clinical scoring system that is utilized to determine the probability of appendicitis. A score of ≥7 indicates a high likelihood of appendicitis.
- Common Positions of the Appendix:
- Retrocecal (most common, easy to visualize).
- Pelvic, paracecal, pre-ileal, and post-ileal (potentially more difficult to visualize).
- Mimics of Appendicitis:
- Mesenteric adenitis, Crohn’s disease, ovarian pathologies, and diverticulitis.
Key Takeaways
- Ultrasound should be the initial imaging in pediatric and pregnant patients.
- CT is the most reliable modality and must be utilized when ultrasound is not conclusive.
- MRI is reserved for situations in which radiation exposure is a problem.
- Radiologists need to be familiar with false negatives and positives, identify complications, and include alternative diagnoses in the report if appendicitis is not suspected.
For further in-depth discussion of imaging in practice, subscribe to Conceptual Radiology and get ahead on your radiology education!
