Can ultrasonic abdomen scan miss appendicitis?

Possibly: It is possible that ultrasound may not be diagnostic for appendicitis. It depends on the tech performing the exam, the patient's body size/habitus, the amount of bowel/stool present, the age of the patient, the location of the appendix, whether free fluid is present, and the confidence of the interpreting radiologist.

Yes: Some studies show that ultrasound only misses appendicitis 10% of the time however this depends on an experienced operator. If the ultrasound is negative other tests are necessary to exclude appendicitis. But if positive, the radiation of a ct scan has been avoided.