Appendicitis

Appendicitis

US – Dilated appendix with appendicolith (right side of longitudinal images) and mural hyperemia. Note the inflamed hyperechoic mesentery surrounding the appendix.

The basic physiology of appendicitis is ischemic necrosis related to luminal obstruction, usually by enteric contents (fecalith)or lymphoid hyperplasia. Because the mucosa is secretory, the appendix becomes progressively dilated. Appendiceal dilation impedes lymphatic and venous drainage, leading to mural edema which eventually compromises arterial perfusion.

The normal appendix measures <6mm although can be larger in patients with chronic constipation (e.g., cystic fibrosis). The central mucosal stripe is echogenic and uninterrupted; fluid is seen in the lumen in about 5% of patients. The mucosal stripe is surrounded by the hypoechoic muscularis propria.

If the appendix is compressible, measures <6mmm and the tip is visualized appendicitis can be excluded. Loss of the echogenic mucosal stripe or focal interruption may reflect early ulceration and necrosis. Appendicoliths are associted with higher incidence of perforation. Loculated periappendiceal fluid is virtually diagnostic of perforated appendicitis. Mural hyperemia on color Doppler indicates inflammation; lack of color flow with gray-scale findings of appendicitis indicates gangrenous appendicitis (mural pneumatosis is also associated with gangrenous appendicitis).

Junewick JJ. Decreasing radiation risks by increasing the use of ultrasound in pediatric imaging. Ultrasound Clin (2009); 4(3):273-284.