Diarrhea; Digestive System Surgical Procedures/methods; Duodenal Neoplasms; Duodenal Ulcer; Esomeprazole/administration & dosage; Gastrinoma; Peptic Ulcer; Rehydration Solutions/administration & dosage; Diagnosis, Differential; Diarrhea/diagnosis; Diarrhea/etiology; Diarrhea/metabolism; Diarrhea/physiopathology; Diarrhea/therapy; Duodenal Neoplasms/metabolism; Duodenal Neoplasms/pathology; Duodenal Neoplasms/physiopathology; Duodenal Neoplasms/therapy; Duodenal Ulcer/diagnosis; Duodenal Ulcer/drug therapy; Duodenal Ulcer/etiology; Duodenal Ulcer/physiopathology; Duodenum/pathology; Duodenum/surgery; Endoscopy, Digestive System/methods; Fluid Therapy/methods; Gastrinoma/metabolism; Gastrinoma/pathology; Gastrinoma/physiopathology; Gastrinoma/therapy; Humans; Male; Middle Aged; Neoplasm Staging; Osmolar Concentration; Peptic Ulcer/diagnosis; Peptic Ulcer/drug therapy; Peptic Ulcer/etiology; Peptic Ulcer/physiopathology; Proton Pump Inhibitors/administration & dosage; Tomography, Emission-Computed, Single-Photon/methods; Tomography, X-Ray Computed/methods; Treatment Outcome; Water-Electrolyte Balance