Can an ectopic pregnancy be mistaken for appendicitis?

Yes: Symptoms of lower abdomen or pelvic pain can be similar. Ultrasound may be difficult to tell fallopian tube from appendix swelling. Best way to tell the difference can be a pregnancy test (positive if ectopic pregnancy).

Initially it can.: A right-sided ectopic adnexal pregnancy can certainly be initially mistaken for acute appendicitis. Imaging with MRI can help differentiate these two life-threatening conditions; if even that is inconclusive, then exploratory laparotomy or laparoscopy should be performed to diagnose and treat the underlying cause at the same time.