Review Question - QID 213609

A 67-year-old man presents to the emergency department with abdominal pain. He states that his pain has been gradually worsening and used to be exacerbated by meals, but now occurs at rest. He also endorses diarrhea and notes blood in his bowel movements at times. He has a past medical history of obesity, diabetes, and hypertension and is generally not compliant with his medications. He was recently treated for sinusitis with amoxicillin. His temperature is 99.0°F (37.2°C), blood pressure is 157/98 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for generalized abdominal discomfort to palpation. Laboratory values are notable for the findings below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 17,500/mm^3
Platelet count: 197,600/mm^3

Serum:
Na+: 141 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 20 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.5 mg/dL
Ca2+: 10.2 mg/dL

A CT scan of the abdomen is performed as seen in Figure A. Which of the following is the most likely diagnosis?