Is the appendix visible on ultrasonography (ultrasound)?

From the Guidelines

The appendix can be visible on ultrasonography, but its visualization may be limited by patient factors or technical limitations, with a sensitivity of 82% when including equivocal results, as reported in the 2024 clinical practice guideline update by the Infectious Diseases Society of America 1. When visible, the appendix appears as a blind-ending tubular structure, and its identification is crucial in evaluating for appendicitis. The use of ultrasonography as the initial imaging modality is suggested in children with suspected acute appendicitis due to its availability, low cost, and high accuracy when yielding a definitive result 1. Some key points to consider when using ultrasonography to visualize the appendix include:

• The appendix typically originates from the base of the cecum, about 2-3cm below the ileocecal valve
• A normal appendix measures less than 6mm in diameter, with a thin wall and compressible lumen
• Ultrasound identification of the appendix is improved when using graded compression technique, which involves applying gentle pressure with the ultrasound probe to displace overlying bowel gas
• Factors such as obesity, excessive bowel gas, or an atypically positioned appendix can limit visualization in some patients
• Ultrasound has advantages of being radiation-free and widely available, making it particularly valuable for pediatric patients and pregnant women 1.

From the Research

Visibility of the Appendix on Ultrasonography

• The visibility of the appendix on ultrasonography (ultrasound) can be affected by various factors, including the skill of the sonographer and the patient's body type 2, 3.
• Studies have shown that ultrasound can be an effective initial imaging modality for diagnosing appendicitis in adults, with sensitivity and specificity rates ranging from 67.65% to 89.6% and 53.0% to 98.41%, respectively 2, 3, 4.
• However, ultrasound may not always be able to visualize the appendix, particularly in patients with a higher body mass index (BMI) or in those with inconclusive ultrasound findings 3, 5.
• In cases where the ultrasound is inconclusive, further imaging or a follow-up visit may be necessary to confirm the diagnosis of appendicitis 2, 5.

Factors Affecting Visibility

• The skill of the sonographer can impact the ability to visualize the appendix on ultrasound, with more experienced sonographers achieving higher sensitivity and specificity rates 2.
• Patient factors, such as age, sex, and BMI, can also affect the visibility of the appendix on ultrasound, with females, older adults, and those with a higher BMI being more likely to have inconclusive or false negative results 3.
• The use of alternative imaging modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI), may be necessary in cases where the ultrasound is inconclusive or the patient has a high risk of appendicitis 3, 6.

Clinical Implications

• The use of ultrasound as an initial imaging modality for diagnosing appendicitis can help reduce the need for CT scans and associated radiation exposure, particularly in pediatric and young adult patients 5, 6.
• However, the limitations of ultrasound, including the potential for inconclusive results, must be taken into account when interpreting the findings and making clinical decisions 2, 3, 4.