Appendiceal wall hyperemia as seen with color Doppler is another common finding in acute appendicitis (Fig. 5).20-22 Appendicoliths, which appear as hyperechoic foci that cast an anechoic shadow, can also sometimes be found within the lumen of an inflamed appendix.²² The presence of pericecal inflammatory changes such as hyperechoic fat or free fluid are often considered suggestive of but not specific for appendicitis.^21,22 Many argue that the appendix must be visualized in order to confirm the diagnosis. Unfortunately, identification of the appendix can often be difficult. The appendiceal visualization rate varies by institution, with one study citing a range of 22%-98%.²³ Interestingly, a recent study by Pacharn et al. reported a 95% NPV for the exclusion of acute appendicitis even if the appendix was not visualized.²⁴ However, such results require a great deal of experience and as a result most still consider an ultrasound without visualization of the appendix to be nondiagnostic. Further imaging is warranted in this situation. Only an ultrasound that demonstrates a compressible, blind-ending appendix in the absence of surrounding inflammatory changes is considered truly normal.^22,25

Limitations to Visualization

Several factors can make diagnosing acute appendicitis with ultrasound challenging. Technical aspects affecting the ability of the sonographer to achieve adequate compression of the RLQ such as obesity, severe pain or abdominal guarding, excessive bowel gas, and an uncooperative patient can all affect the accuracy of the ultrasound.^26,27 Operator experience can also affect the study result.

Adjuvant techniques exist that can assist in the visualization of the appendix when one is unable to identify it utilizing graded compression alone. Posterior manual compression can be performed by placing one hand on the patient’s back, posterior to the RLQ, and applying forced compression in the anteromedial direction while still applying graded compression with the transducer on the anterior abdominal wall (Fig. 6). This causes displacement of the RLQ bowel structures and can reduce the distance from the transducer to the retrocecal or retrocolic spaces, potentially increasing the resolution of the appendix. Because the most common location of the appendix is retroileal and subcecal, this technique is effective in a majority of patients. However, it is limited when the appendix lies inferior to the iliac crest because the bony pelvis will not allow anterior displacement in this position.^21,28