Gastrinoma, also known as Zollinger-Ellison syndrome (ZES), originates from G cells. It is the second most common functional pancreatic neuroendocrine neoplasm (pNEN) after insulinoma. Gastrinomas are often sporadic but may also occur in association with multiple endocrine neoplasia type 1 (MEN-1). Between 60% and 90% of gastrinomas are malignant and often present with lymph node or liver metastases. Approximately 90% of gastrinomas are located within the gastrinoma triangle, which is defined by the following anatomical boundaries: superiorly by the junction of the cystic duct and common bile duct, inferiorly by the intersection of the descending and horizontal portions of the duodenum, and medially by the junction of the pancreatic neck and body.
Diagnosis
The diagnosis of gastrinoma primarily relies on clinical presentation and laboratory testing.
Clinical Features
The predominant clinical manifestations include refractory peptic ulcers and diarrhea, with the ulcers most commonly occurring in the duodenal bulb. Abdominal pain is reported by most patients, and approximately 70% of individuals experience diarrhea, which is related to excessive gastric acid secretion. Complications such as bleeding, perforation, or pyloric obstruction occur in about 60% of cases.
Laboratory Tests
Gastric Fluid Analysis
A basal acid output (BAO) greater than 15 mmol/h in patients without a history of gastric surgery, or greater than 5 mmol/h in patients who have undergone partial gastrectomy, supports the diagnosis. A BAO-to-maximal acid output (MAO) ratio (BAO/MAO) greater than 0.6 also supports the diagnosis.
Measurement of Gastrin Levels
A fasting serum gastrin level exceeding 10 times the upper limit of normal, along with a gastric pH of ≤2, confirms the diagnosis. In patients with a fasting gastrin level below 10 times the upper limit of normal but with a gastric pH of ≤2, basal acid output (BAO) should be measured. A secretin stimulation test (an increase in fasting serum gastrin of >120 pg/mL) may also help establish the diagnosis.
Tumor Localization
Abdominal ultrasound, CT, MRI, somatostatin receptor imaging (SRI), and endoscopic ultrasound (EUS) are useful for localizing the tumor.
Treatment
The treatment of gastrinoma focuses on controlling excessive gastric acid secretion and surgical tumor management.
Medical Therapy
Proton pump inhibitors (PPIs) and H2 receptor antagonists effectively reduce gastric acid secretion, with PPIs being the preferred option.
Surgical Treatment
Given the malignant potential of gastrinomas, curative resection with regional lymph node dissection is the preferred approach, which significantly prolongs survival. In cases where complete resection is not feasible, debulking surgery may be performed to alleviate symptoms.