A 23-year-old male presents to the emergency department with complaints of progressively worsening abdominal pain and nausea over the past 12 hours. The nurse takes his vital signs and notes that he has a fever. The abdomen examination reveals a somewhat rigid abdomen with guarding and extreme tenderness in the right lower quadrant midway between the umbilicus and the superior iliac spine. Normal bowel sounds are present. Based on this history and presentation, which of these medical emergencies should the nurse suspect?