Eighty percent to 90% of all gastrinomas are located in the so-called gastrinoma triangle, which includes the duodenum, the pancreatic head, and the hepatoduodenal ligament.28 In contrast to previous reports, which stated that 80% of all gastrinomas are localized in the pancreas and only 20% in the duodenum, Sugg and colleagues29 showed that 70% to 80% of gastrinomas are found in the duodenal wall. The size of gastrinomas varies with the site of the tumors; pancreatic gastrinomas are often larger than 1 cm, whereas gastrinomas of the duodenum are usually smaller than 1 cm.29 Therefore, it is nearly impossible to identify duodenal gastrinomas by preoperative imaging procedures.30

In 1999, Norton and colleagues31 presented their results of surgical resection in more than 150 patients with ZES. In patients with sporadic ZES gastrinomas were detected by US in 24% (Fig. 80-3), by CT in 39% (Fig. 80-4), by MRI in 46%, and by SA in 48%. In approximately one third of patients with sporadic gastrinomas, the results of conventional imaging studies were negative. Different studies on patients with ZES confirmed these results.3,4,19,29,32 As mentioned previously, ES is able to detect even small tumors in the pancreas. After first reports,3,4 many studies confirmed these results; for example, Zimmer and colleagues found pancreatic gastrinomas by ES in 79%.33 Anderson and coworkers5 were able to localize all 36 pancreatic gastrinomas investigated by ES, whereas SA detected only 44% of the lesions.

FIGURE 80-3. Transverse preoperative ultrasonography (5-MHz linear-array transducer) shows typical hypoechoic gastrinoma (20 mm) (TU) within the echogenic parenchyma of the pancreatic head (PA). CO = confluence.
FIGURE 80-4. Enhanced computed tomographic scan demonstrates a 16-mm enhancing gastrinoma in the pancreatic head.

The European multicenter trial to evaluate the efficacy of SRS showed positive results for pancreatic gastrinomas in 73%.24 In a prospective study comparing the sensitivity of SRS with that of CT, MRI, US, and SA in detection of primary and metastatic pancreatic gastrinomas, SRS altered clinical management in 47% of instances and had superior sensitivity and specificity.34 Cadiot and coauthors35 compared the results of SRS with those of conventional imaging techniques, including ES, and with surgical findings in 21 consecutive patients with ZES. SRS added information to other imaging results and improved the preoperative detection of extrapancreatic gastrinomas. By combining SRS with ES, they were able to detect 90% of the tumors. Our experiences with SRS do not show any advantage when compared with the localization methods mentioned previously.32 The gastrinomas that were visualized were either larger than 1 cm in diameter or had widespread metastases (Fig. 80-5). Invasive localization methods, such as PVS and the selective intra-arterial injection of secretin combined with venous sampling (Imamura technique), show comparatively high sensitivity of 77% and 100%, respectively;

FIGURE 80-5. Somatostatin receptor scintigraphy shows two circular enhancements that represent two retroperitoneal tumors (arrow). The primary tumor, a gastrinoma, could not be identified.

however, they allow only regionalization and not exact localization of the tumors29'31-36'37 38 (Table 80-2).

Again it seems that the best method for localization is surgical exploration and IOUS (Fig. 80-6). The sensitivities of palpation and IOUS are 91% and 95%,39 respectively. We recommend a surgical approach similar to that used for patients with insulinomas, including preoperative US or CT scan to rule out large tumors with liver metastases and then IOUS. A study from the National Institutes of Health tested four different intraoperative procedures.29 All 31 duodenal tumors were detected after longitudinal incision of the second part of the duodenum and separate palpation of the posterior and anterior walls. The second best result was achieved by intraoperative endoscopy and transillumination of the duodenal wall (64%). Standard palpation and IOUS, on the other hand, detected only 61% and 26% of gastrinomas, respectively. Norton and colleagues underlined the importance of duodenotomy (DUODX) in patients with ZES.40 They performed DUODX in 79 patients and did not perform DUODX in 64 patients. Gastrinoma was found in 98% with DUODX compared with 76% with no DUODX. They could show that the use of routine DUODX increases the short-term and long-term cure rate.

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