Review Question - QID 214629

A 62-year-old woman presents to the emergency department with severe abdominal pain. For as long as she can remember, she has had aching abdominal pain associated with meals, but today she awoke suddenly with unrelenting severe pain and associated nausea and vomiting. She has a history of atrial fibrillation and chronic back pain. Her medications include verapamil and naproxen. She smokes 1 pack per day and drinks 1-2 beers daily. Her temperature is 99.4°F (37.4°C), blood pressure is 169/83 mmHg, pulse is 91/min, and respirations are 18/min. On exam, her heart rate and rhythm are regular, and her lungs are clear to auscultation bilaterally. Her abdomen is rigid with involuntary guarding and rebound tenderness. An abdominal radiograph is shown in Figure A. Which of the following is the most likely cause of this patient's presentation?