US depiction of the appendix: role of abdominal wall thickness and appendiceal location

The purpose of the present study was to correlate direct measurements of abdominal wall fat at the site of exam and appendiceal position with ultrasound (US) visualization of the appendix. The study took place at a large, urban pediatric teaching hospital. Demographic and imaging data of all patients who underwent both US and CT examinations within a 72-h period to evaluate for appendicitis were assessed. Two hundred eighteen patients met study criteria. Greater abdominal wall fat (p < 0.001) was observed in the subjects where the appendix was not visualized with ultrasound (17.04 mm, SD ± 13.52) than in subjects where the appendix was visualized with ultrasound (11.75 mm, SD ± 11.81) was significant. Using ROC curve analyses, there was no abdominal fat thickness cutoff threshold above which the appendix was significantly unlikely to be seen using US. Retrocecal location of the appendix was found to impair appendiceal visualization with US for both normal and inflamed appendices. Increased abdominal wall fat thickness was associated with decreased US appendiceal visualization rates, although there was no fat thickness value above which we could predict that the appendix would not be visualized with US. In patients with retrocecal appendices, the difference in visualization rates was significantly worse regardless of whether the appendix was normal or inflamed.