Lymphoid Hyperplasia of the Appendix: A Potential Pitfall in the Sonographic Diagnosis of Appendicitis

The objective of this study was to test the hypothesis that thickening of the lamina propria, a finding produced by lymphoid hyperplasia, is significantly associated with false-positive sonographic diagnoses of appendicitis in 6- to 8-mm noncompressible appendixes.

Sonograms of 119 consecutive patients with suspected appendicitis and 6- to 8-mm noncompressible appendixes were retrospectively blindly evaluated for thickening of the lamina propria (short axis thickness ≥ 1 mm). The reference standard for appendicitis was pathologic analysis of resected specimens. Results were compared with the two-tailed Fisher exact test.

Thirty-one patients (26.1%) had a thickened lamina propria and 88 (73.9%) did not. Of the 27 pediatric patients with a thickened lamina propria, five (18.5%) had true-positive and 22 (81.5%) had false-positive sonograms for appendicitis; among the 55 pediatric patients without a thickened lamina propria, 27 (49.1%) had true-positive and 28 (50.9%) had false-positive sonograms for appendicitis (p = 0.009). Similar differences in adult patients were not statistically significant. All five pediatric patients with appendicitis and thickened lamina propria also showed two or more findings of periappendiceal fluid, hyperechoic periappendiceal fat, or mural hyperemia on color Doppler examination, compared with two of 22 similar pediatric patients without appendicitis (p < 0.001).

Lymphoid hyperplasia may result in a noncompressible appendix 6-8 mm in diameter and may be misdiagnosed as appendicitis in pediatric patients. True-positive diagnoses of appendicitis can be accurately identified by the presence of at least two additional findings from the group of periappendiceal fluid, hyperechoic periappendiceal fat, and mural hyperemia. Identifying the characteristic sonographic appearance of lymphoid hyperplasia may help prevent false-positive misdiagnoses of appendicitis.