Which imaging modality has a sensitivity of 75-90% for diagnosing appendicitis?

• A. Ultrasound
• B. CT scan
• C. MRI
• D. X-ray

Answer: (A)

Imaging choice for suspected appendicitis hinges on how accurately the test can identify the condition while also considering safety. Ultrasound often falls in the 75-90% sensitivity range, especially in children and lean adults, making it the most appropriate first-line test when a moderate level of diagnostic yield is acceptable and avoiding radiation is a priority.

Ultrasound is noninvasive, portable, and free of ionizing radiation, so it’s particularly favored in younger patients and pregnant individuals. A skilled exam looks for a next-to-compressible, blind-ended tubular structure in the right lower quadrant that is usually greater than about 6 mm in diameter, with wall thickening, periappendiceal fluid or fat stranding, and sometimes an appendicolith. It can also reveal alternative causes of pain, such as gynecologic pathology.

However, ultrasound has limitations. Its accuracy depends on the operator and patient body habitus; in adults with obesity or significant bowel gas, visualization of the appendix can be poor, leading to nondiagnostic results. When ultrasound is nondiagnostic or the suspicion remains high despite a negative ultrasound, CT is often pursued because it has higher overall sensitivity and specificity (typically above 95%), though it involves ionizing radiation. MRI provides excellent sensitivity without radiation and is valuable in pregnancy or when CT is contraindicated, but it may be less readily available emergently and can be more time-consuming or costly. Plain X-ray has very limited utility for appendicitis and is not relied upon to diagnose it.

So, given the stated sensitivity range, ultrasound is the best choice for its balance of diagnostic performance and safety in many patient populations.