Preoperative evaluation for gastrinoma
CT scan with intravenous and oral contrast is routine in the preoperative evaluation for gastrinoma resection to rule out metastatic disease, and its accuracy depends on the size of the gastrinoma. In some cases, magnetic resonance imaging (MRI) is used because it is more sensitive than CT scan for liver metastases. The advent of somatostatin receptor scintigraphy (octreotide) scan has greatly improved the preoperative localization of gastrinomas. This study relies on the high density of somatostatin receptors on gastrinomas and uses the radiolabeled synthetic somatostatin analog, iodine-125—[ 125 I]octreotide—to identify primary as well as metastatic gastrinomas.
Recent studies have demonstrated that somatostatin receptor scintigraphy has high sensitivity and specificity for detection of primary and metastatic gastrinomas and is the initial imaging modality of choice for localization. It also evaluates the extent of somatostatin receptors and addresses the need for somatostatin-based therapies. Endoscopic ultrasound has recently been used to localize gastrinomas; however, it is highly operator dependent and does not reliably identify small tumors in the duodenum. Intraoperative upper endoscopy with transillumination or intraoperative ultrasound may also help to localize small duodenal gastrinomas. More recently, a modification of octreotide scanning has become available as an adjunct to intraoperative localization. A handheld gamma-detecting probe is used intraoperatively to localize gastrinomas after the injection of [ 125 I]octreotide.