Q. A 25-year-old male presents to the emergency department complaining of severe abdominal pain. The pain started suddenly and has been constant for the past 12 hours. The patient reports that the pain is accompanied by nausea, vomiting, loss of appetite, and a low-grade fever. He has been unable to pass gas or stool and has not had a bowel movement for the past two days. The patient is otherwise healthy and has no significant past medical history. He has never had any abdominal surgery or been diagnosed with any gastrointestinal disorders. The patient is a non-smoker and does not drink alcohol. He works as a construction worker and reports no recent travel or exposure to any infectious agents. On physical examination, his vital signs are within normal limits. The patient appears agitated and uncomfortable. His abdomen is distended, and there is diffuse tenderness to palpation. The patient has a positive Rovsing sign, and there are no visible peritoneal signs. You order a complete blood count and C-reactive protein, as well as an ultrasound and CT scan of his abdomen (see image). The results of the CBC and CRP are consistent with inflammation and infection. Based on the information available to you at this point in time, which of the following is the most likely diagnosis?