A 23 year-old woman presents to the emergency room with severe lower right abdominal pain for the last six hours. She had intermittent lower abdominal pain for three days but never been severe like this time. Her last menstrual period was three months ago and before that she had regular 28 day periods. On physical examination, her vital signs are within normal limits and she has a local tenderness on the lower abdomen with no rebound. On pelvic examination, there is a tender small-sized mass felt in the right vaginal fornix.
What is the most likely diagnosis?
A- Acute appendicitis
B- Ovarian cyst
C- Ectopic pregnancy
E- Pelvic abscess
Amenorrhea of 3 months is a clue of pregnancy. Pelvic examination confirms ectopic pregnancy.
The correct answer is C