Might an ultrasound and a ct scan give different results when looking for appendicitis?

Absolutely.: A sonogram is not typically the best imaging study to look for appendicitis. It is often done when evaluating pelvic/lower abdominal pain in women to look for ovarian cysts. It is definitely possible to have different results on different studies. If that is the case, you would need a good clinical doctor to evaluate the entire picture - not just the imaging results, to make a diagnosis and tx p.

Yes-CT more reliable: A ct scan is a much better test than an ultrasound to check for appendicitis. However, the radiation exposure from a ct is not trivial. Therefore, we often try an ultrasound first in children (& during pregnancy); if the ultrasound shows appendicitis, it's reliable; if not, we then may get a ct. Ultimately, appendicitis is a clinical diagnosis, combining history, exam, labs+/- ct or u/s to decide.