Purpose or Case Report: Ultrasound carries high sensitivity in diagnosing acute appendicitis in pediatric patients and is increasingly being used as the preferred method of diagnosis since it does not use ionizing radiation. Although an enlarged diameter of the appendix and non-compressibility are the primary indicators of appendicitis, they do not have perfect specificity. Therefore, secondary features of appendicitis are crucial in supporting the diagnosis of appendicitis. The most sensitive secondary finding of appendicitis is inflammatory echogenic periappendiceal fat. Other secondary signs of appendicitis are either infrequently present, like wall hyperemia, or entirely nonspecific, like periappendiceal free fluid. Improving diagnostic accuracy of appendicitis with additional secondary supportive signs would be helpful. We have subjectively observed that appendix shape may be a helpful secondary sign of appendicitis, and that in certain cases it forms a C-shape or curved appearance when inflamed. It mimics the appearance of the letter ‘C’ and hence, we termed it, the “C sign.” Retrospective review of 999 ultrasound appendix studies that were conducted in our hospital from January 1, 2022, to March 31, 2022, with 150 sonographically positive acute appendicitis cases, we found 10 patients with the positive C sign and deemed positive by US and pathologically to be acute appendicitis. It seems by observation that this sign is not sensitive but specific when found, for acute appendicitis. One probable explanation for this configuration is loop separation that occurs when the proximal and distal ends of the appendix are separated either by inflamed fat or wall thickening. Herein, we show a few examples of the appendiceal “C-sign”, describe our observations, and suggest its potential use as an additional secondary sign of appendicitis.
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