Gastrinoma

Clinical
The Zollinger-Ellison syndrome is caused by a gastrin-secreting tumor. Most gastrinomas are malignant. About 25% of gastrinomas occur in a setting of MEN-I syndrome and a patient presenting with a gastrinoma probably should
be investigated for this syndrome. Gastrinomas tend to be multiple when part of MEN-I syndrome. The risk of gastrinoma malignancy, growth rates, and high prevalence in the duodenum seen in MEN-I patients cannot be extrapolated to patients with isolated gastrinomas. Even with liver metastases these tumors grow slowly, and prolonged survival is feasible.
Occasionally a small gastrinoma is discovered in a lymph node; most of these are metastatic foci, although a rare one is believed to represent a primary tumor and excision of that lymph node should be curative.With such a scenario a search for a primary gastrinomas should, of course, be performed. A review of patients with gastrinoma/ Zollinger-Ellison syndrome found that a correct preoperative diagnosis is made in about half of these patients, and about half of these tumors are <20 mm in diameter; although about 40% had metastases, the 10-year survival rate was 64%. These patients develop recurrent, multiple ulcers in atypical locations. They have basal gastric acid hypersecretion and a markedly elevated fasting serum gastrin level, with values considerably greater than seen after a truncal vagotomy or proximal gastric vagotomy.
In the absence of metastases, unless surgery s contraindicated, even with negative preoperative imaging studies these patients probably should undergo exploratory laparotomy, with the aim of a curative resection. Previously, if excision was not feasible, a total gastrectomy was performed for symptom control; today total gastrectomy is rarely performed and in most patients gastric acid hypersecretion is managed with H2 receptor antagonists. Thus with suspected liver metastases a biopsy establishes the
diagnosis and these patients are then treated medically.
Many of these tumors contain somatostatin receptors, and somatostatin analogues are potential therapeutic agents. Using an autoradiography technique, both pancreatic carcinomas and gastrinomas expressed specific
somatostatin receptors; in gastrinomas, octreotide inhibited iodine-125–somatostatin- 28 binding similar to somatostatin-28, but little competitive binding of I-125–somatostatin-28 was evident in carcinomas, suggesting that
somatostatin receptors in gastrinomas differ from those in carcinomas.
Imaging A barium study detects gastritis, often severe, and peptic ulcer disease, especially in postbulbar regions.Hyperacidity is also associated with reflux esophagitis in many of these patients. The imaging procedures useful in detecting a gastrinoma include CT, endoscopic US, MRI, indium-111–octreotide scintigraphy, and selective arterial secretin injection, with the initial study of choice often being octreotide scintigraphy. Still, only approximately half of gastrinomas are detected with these studies.
image
Radiology images of gastrinoma in a 75-year-old man. Transverse precontrast CT identifies enlargement of the pancreatic head (arrow). Initially believed to represent a pancreatic carcinoma, biopsy suggested a gastrinoma.

In patients with Zollinger-Ellison syndrome, duodenal, lymph node, and pancreatic gastrinomas were eventually found in 42%, 38%, and 17% of patients, respectively. Of these tumors, endoscopic US detected 50% of duodenal wall tumors while conventional endoscopy detected 40%. Endoscopic US detected 75% of pancreatic tumors while CT detected 25%; endoscopic US detected 62% of lymph node tumors while CT detected none.
The authors concluded that endoscopic US is the imaging technique of choice for preoperative imaging of gastrinomas. At times intraoperative US is necessary in locating small gastrinomas.
Similar to other solid pancreatic tumors, gastrinomas are hypointense on T1- and hyperintense on T2-weighted fat-suppressed MRI. In distinction to most other neuroendocrine tumors, gastrinomas enhance postcontrast in a ring pattern. Such ring-like enhancement is also seen in liver metastases; this finding is not specific for gastrinomas but is also occasionally found with other neuroendocrine tumors. An occasional cystic component is detected in a gastrinoma. Indium-111–pentetreotide scintigraphy is probably superior to CT in localizing gastrinomas; scintigraphy can detect duodenal tumors several millimeters in size.Nevertheless, In-111–pentetreotide is not foolproof. In a patient with a previous partial pancreatectomy and splenectomy and now presenting with Zollinger-Ellison syndrome, In-111– pentetreotide scintigraphy revealed nodular increased uptake in an accessory spleen.
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