Magnetic resonance imaging
Magnetic resonance imaging (MRI) use has become increasingly common for diagnosis of appendicitis in children and pregnant patients due to the radiation dosage that, while of nearly negligible risk in healthy adults, can be harmful to children or the developing baby. In pregnancy, it is more useful during the second and third trimester, particularly as the enlargening uterus displaces the appendix, making it difficult to find by ultrasound. The periappendiceal stranding that is reflected on CT by fat stranding on MRI appears as an increased fluid signal on T2 weighted sequences. First trimester pregnancies are usually not candidates for MRI, as the fetus is still undergoing organogenesis, and there are no long-term studies to date regarding its potential risks or side effects. X-ray
In general, plain abdominal radiography (PAR) is not useful in making the diagnosis of appendicitis and should not be routinely obtained from a person being evaluated for appendicitis. Plain abdominal films may be useful for the detection of ureteral calculi, small bowel obstruction, or perforated ulcer, but these conditions are rarely confused with appendicitis. An opaque fecalith can be identified in the right lower quadrant in fewer than 5% of people being evaluated for appendicitis. A barium enema has proven to be a poor diagnostic tool for appendicitis. While failure of the appendix to fill during a barium enema has been associated with appendicitis, up to 20% of normal appendices do not fill. Scoring systems
Several scoring systems have been developed to try to identify people who are likely to have appendicitis.
Computed tomography
Where it is readily available, computed tomography (CT) has become frequently used, especially in people whose diagnosis is not obvious on history and physical examination. Although some concerns about interpretation are identified, a 2019 Cochrane review found that sensitivity and specificity of CT for the diagnosis of acute appendicitis in adults was high. Concerns about radiation tend to limit use of CT in pregnant women and children, especially with the increasingly widespread usage of MRI.The accurate diagnosis of appendicitis is multi-tiered, with the size of the appendix having the strongest positive predictive value, while indirect features can either increase or decrease sensitivity and specificity. A size of over 6 mm is both 95% sensitive and specific for appendicitis.However, because the appendix can be filled with fecal material, causing intraluminal distention, this criterion has shown limited utility in more recent meta-analyses. This is as opposed to ultrasound, in which the wall of the appendix can be more easily distinguished from intraluminal feces. In such scenarios, ancillary features such as increased wall enhancement as compared to adjacent bowel and inflammation of the surrounding fat, or fat stranding, can be supportive of the diagnosis. However, their absence does not preclude it. In severe cases with perforation, an adjacent phlegmon or abscess can be seen. Dense fluid layering in the pelvis can also result, related to either pus or enteric spillage. When patients are thin or younger, the relative absence of fat can make the appendix and surrounding fat stranding difficult to see.