A 37-year-old woman was admitted to the emergency department with high fever (39.5deg C), nausea, and vomiting. Physical examination revealed increased abdominal pain in the paraumbilical region, rebound tenderness over McBurney's point, and a positive psoas test. Blood tests showed marked leukocytosis. Which of the following is the most likely diagnosis?

Appendicitis is often characterized by acute inflammation and is indicated with both a positive psoas test and rebound pain over McBurney's point. McBurney's point lies 1 inch lateral to the midpoint of an imaginary line in the right lower quadrant, joining the anterior superior iliac spine and the umbilicus. In patients with appendicitis, rebound tenderness may be felt over McBurney's point after quick, deep compression of the left lower quadrant. An ectopic pregnancy would be associated with generalized abdominal pain instead of the localized pain felt over McBurney's point. Cholecystitis results from an inflammation of the gallbladder and would result in pain over the epigastric region shifting to the right hypochondriac region. Kidney stones result in referred pain to the lumbar or possibly inguinal regions. Perforation of the duodenum could result in pain to palpation of the abdomen, together with adynamic (paralytic) ileus, rigidity of the abdominal wall, and referral of pain to the shoulder.