PURPOSE
To evaluate the US findings that can help differentiate lymphoid hyperplasia of appendix from acute appendicitis.

MATERIAL AND METHOD
A total 1230 patients suspected of having appendicitis were performed appendectomy between November 1999 and March 2008, US findings of 27 patients with pathologically proven lymphoid hyperplasia of appendix and 52 patients with acute appendicitis as a control group were retrospectively reviewed by two radiologist’s consensus that were blinded to the pathologic results. US findings were compared between two groups. This review was based on a set of twelve criteria derived from reports in the literature of diagnostic findings of appendicitis: maximal diameter, wall thickness, intraluminal contents, periappendiceal inflammation and fluid, lymph nodes, appendicolith, shape in transverse scan, compressibility, increased blood flow on color Doppler ultrasonography, wall thickening of cecum and terminal ileum. Statistical analysis were performed using the Student’s t test and Pearson’s chi-square test.

RESULT
Compared with acute appendicitis, US findings of lymphoid hyperplasia in appendix showed less maximal diameter (7.14±1.22mm vs 9.37±1.80mm, p<0.001) and wall thickness(1.38±0.36mm vs 1.74 ± 0.56mm, p=0.001), and significant differential findings between two groups also showed as follows: Periappendiceal inflammation(3.7% vs 59.6%, p<0.001), intraluminal air(44.4% vs 15.4%, p=0.006), oval shape in transverse scan(41.7% vs 10.0%, p=0.002), increased blood flow on color doppler ultrasonography(25.0% vs 66.7%, p=0.03).

CONCLUSION
US findings are useful in the differentiation of lymphoid hyperplasia in appendix from acute appendicitis.