abdomens. 2,3 Placing the patient in a leſt lateral decubitus can help position the cecum and TI medially, improving access to the retrocecal region. 3 If the appendix remains occult, repositioning the patient may cause bowel gas movement, enhancing visualization. 2 Some have suggested adding a posterior approach. 11 Once identified, the appendix should be documented in grayscale and color Doppler images. The Doppler pulse repetition frequency should be very low. Longitudinal images showing the blind-ending tip (Figure 4) and, if possible, origin from the cecum will prove that the structure identified is the appendix and not another piece of bowel (Figure 5). The presence of hyperemia is best demonstrated in longitudinal images. Compression images showing transverse luminal diameter should be obtained side-by-side (Figure 5). Morrison pouch and the pelvis are commonly examined with low-frequency transducers and a deeper field of view to evaluate for free fluid or abscess. 3 The appendix may be seen suspended within any free fluid. 2 Normal Appendix The normal appendix is a compressible, blind-ending, tubular structure featuring 5 distinct layers in the wall, although only 3 may be visible. The innermost layer is a hyperechoic mucosal linear structure containing lymphoid tissue. 2 Appendiceal diameter is typically less than 6 mm and does not change with age. 12 The maximal mural thickness, however, does vary with age and a maximum of 3 mm should be considered normal for those under 6 years old. 12,13 There should be minimal color Doppler signal in the appendix wall (Figure 5). Gas in the appendix typically indicates the absence of acute appendicitis. 14 The appendix is oſten enlarged in patients with cystic fibrosis in the absence of Figure 4. Longitudinal image of a normal appendix (calipers) with expected wall structure and echogenic luminal contents Figure 5. Transverse images (A). Compressibility should be assessed by measuring the diameter of the appendix, ideally in a side-by-side grayscale view (left, without compression; right, with compression). Longitudinal images showing the cecum origin in grayscale (B) and the blind-ending tip on color Doppler (C). Note that the appendix is not displaced from the adjacent structures by inflamed fat or edema; there is no fat stranding. A B C Pediatric Appendicitis US: Practical Considerations 8 Applied Radiology November / December 2024