A 68-year-old male musician presents to the emergency department with a sudden onset of colicky abdominal pain and massive vomiting of 4-hour duration. Examination shows an elevated WBC of 13,200 with a HCT of 45%. Electrolytes and blood urea nitrogen (BUN) are normal. An erect film of the abdomen reveals dilatation of the stomach with distended loops of bowel. What is his clinical diagnosis?