Appendicitis is common. The typical features are of periumbilical pain migrating to the right iliac fossa. This is associated with anorexia and vomiting, which occurs after the pain. Diagnosis is more difficult when these features are absent, the inflammatory markers are not raised (presumably early in the disease process) or when the patient is pregnant. If an intrauterine pregnancy is not known, a pregnancy test should be performed and an ectopic pregnancy should be considered. Both CT and ultrasound are sensitive and specific for appendicitis(1,2).

Figure 1: (above) Note the terminal ileum and ileocaecal valve (short arrow) and the thickened appendix (long arrow) with associated inflammatory change.

To find the appendix on ultrasound use a linear high frequency probe (e.g. 9 MHz) and apply graded compression as you follow the caecum down. Often the appendix is located at the site of maximum tenderness. The appendix, when inflamed, should be seen as a tubular, blind ending, non-compressible structure that measures 6 mm or more in diameter. This is both sensitive and specific for appendicitis, but does require practice. Look for collections throughout the rest of the abdomen and pelvis.

In the following gallery the third image demonstrates a perforated appendix with possible appendicolith. When measuring the appendix measure from the outer hyperechoic layer to its corresponding layer on the opposite side(3).

References

1. Rao PM, Rhea JT, Novelline RA. Sensitivity and specificity of the individual CT signs of appendicitis: experience with 200 helical appendiceal CT examinations. J Comput Assist Tomogr. 1997;21(5):686-692.
2. Yu S-H, Kim C-B, Park JW, Kim MS, Radosevich DM. Ultrasonography in the Diagnosis of Appendicitis: Evaluation by Meta-analysis. Korean J Radiol. 2005;6(4):267-277.
3. Rettenbacher T, Hollerweger A, Macheiner P, et al. Outer Diameter of the Vermiform Appendix as a Sign of Acute Appendicitis: Evaluation at US1. Radiology. 2001;218(3):757 -762.